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C6 THE RATE AND EXTENT OFCHEMICAL CHANGEQuestion Practice
Name: ________________________
Class: ________________________
Date: ________________________
Time: 211 minutes
Marks: 206 marks
Comments: HIGHER TIER
Page 1 of 73
A student investigated the rate of the reaction between magnesium and dilute hydrochloric acid.The student used the apparatus shown in Figure 1 to collect the gas produced.
Figure 1
(a) Outline a plan to investigate how the rate of this reaction changed when the concentrationof the hydrochloric acid was changed.
• Describe how you would do the investigation and the measurements you wouldmake.
• Describe how you would make it a fair test.
You do not need to write about safety precautions.
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(6)
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Page 2 of 73
(b) Figure 2 shows the gas syringe during one of the experiments.
Figure 2
What is the volume of gas collected?
Tick one box.
5.3 cm3
6.0 cm3
6.5 cm3
7.0 cm3
(1)
Page 3 of 73
(c) Figure 3 shows the student’s results for one concentration of hydrochloric acid.
Figure 3
The table below shows the student’s results when the concentration was two times greaterthan the results on Figure 3
Time in seconds Volume of gas produced in cm3
0 0
10 35
15 52
20 80
30 87
Plot the results in the table above on the grid in Figure 3.Draw a line of best fit.
(3)
Page 4 of 73
(d) Give one conclusion about how the rate of reaction changed when the concentration ofhydrochloric acid was changed.
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(1)
(Total 11 marks)
The rate of chemical reactions can be changed by changing the conditions.
(a) Methane burns in oxygen to produce carbon dioxide and water.
The activation energy for the reaction is 2648 kJ / mol.
The reaction gives out 818 kJ / mol of energy.
The figure below shows the reaction profile for this reaction.
Complete the reaction profile.
Draw arrows to represent:
• the activation energy
• the energy given out.
(4)
2
(b) What percentage of the activation energy is the energy given out?
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(1)
Page 5 of 73
(c) Calcium carbonate decomposes when it is heated:
The decomposition of calcium carbonate is an endothermic reaction.
How would the reaction profile for decomposition of calcium carbonate be different from thereaction profile of methane burning in oxygen?
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(1)
(d) Catalysts are used in chemical reactions in industry.
Give two properties of catalysts.
For each property, explain why it makes the catalyst useful in industry.
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(4)
(e) Enzymes are biological catalysts.
What type of molecule is an enzyme?
Tick one box.
Carbohydrate
Hydrocarbon
Lipid
Protein
(1)
Page 6 of 73
(f) If enzymes are denatured they stop working.
Give two ways an enzyme can be denatured.
1. _________________________________________________________________
2. _________________________________________________________________
(2)
(g) An enzyme called lactase catalyses the reaction that breaks down lactose to smallermolecules.
One model used to explain how enzymes affect reactions is called the lock and key model.
Use the lock and key model to explain why lactase cannot be used to speed up allchemical reactions.
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(3)
(Total 16 marks)
A student investigates how the concentration of an acid affects the rate of a reaction.
This is the method used.
1. Put a 3 cm piece of magnesium ribbon into a conical flask.
2. Add 50 cm3 of 0.5 mol / dm3 hydrochloric acid to the flask.
3. Collect and measure the volume of gas produced at 10 second intervals.
4. Repeat with different concentrations of hydrochloric acid using the same length ofmagnesium ribbon and volume of acid.
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Page 7 of 73
The student’s results are shown in the figure below.
(a) How do the results show that increasing the concentration of acid increases the rate ofreaction?
You must use data from the graph in your answer.
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(2)
Page 8 of 73
(b) Explain why the rate of reaction changes as the concentration of the acid increases.
You should answer in terms of particles.
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(3)
(c) Student A said that the final volume of gas collected was lower for a concentration of 0.5mol dm3 because the reaction had not finished.
Student B said it was because all the acid had reacted.
Describe further experimental work the students could do to find out which student wascorrect.
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(2)
(Total 7 marks)
Page 9 of 73
Amylase catalyses the breakdown of starch into sugars.
A student investigated the effect of amylase on the reaction at different temperatures.
Figure 1 shows the apparatus the student used.
Figure 1
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This is the method used.
1. Put starch suspension into a test tube.
2. Add amylase solution.
3. Put the test tube in a beaker of water at 15 °C.
4. Remove a small sample of the mixture every 30 seconds and put in a spotting tile.
5. Test the sample for starch.
6. Time how long it takes to break down all of the starch in the mixture.
7. Repeat steps 1–5 at 20 °C, 25 °C and 30 °C.
8. Repeat for each temperature twice more.
Page 10 of 73
The table below shows the student’s results.
Time taken until there was no starch in the sample in
minutes
Temperature in°C
Test 1 Test 2 Test 3 Mean
15 6.1 9.4 10.0 8.5
20 4.8 5.0 4.6 4.8
25 3.0 2.5 3.0 3.2
30 1.5 2.0 2.0
(a) One of the results in the table above is anomalous.
Draw a ring around the anomalous result.
(1)
(b) Calculate the mean for 30 °C.
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(1)
Page 11 of 73
(c) Figure 2 shows a graph of the student’s results.
Figure 2
Use the graph to predict how long it would take to break down all of the starch at 10 °C.
Time = _________________ minutes
(1)
(d) The student tested samples of the mixture for starch every 30 seconds.
In each test she added one drop of iodine to the sample in the spotting tile.
Predict the colour of the samples from the 20 °C test at 4.0 minutes and 7.0 minutes.
Colour at 4.0 minutes __________________________________________
Colour at 7.0 minutes __________________________________________
(2)
Page 12 of 73
(e) The student did a fourth test at 30 °C.
In this test the starch did not break down, even after 45 minutes.
Why did the amylase not break down the starch in this test?
Tick one box.
The amylase solution and the starch suspension were mixed before thestart of the experiment.
The amylase solution had been prepared with water at 95 °C.
The amylase solution had been prepared with water at 20 °C.
The amylase solution had been stored in the fridge.
(1)
(f) The student made the following conclusion about the optimum temperature for amylase towork at.
‘Amylase works fastest at 40 °C’
Her teacher said that this is not a valid conclusion from her results.
Describe how the student could change her method to give results that would improve thevalidity of her conclusion.
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(6)
(Total 12 marks)
Page 13 of 73
A student investigated the rate of reaction between sodium thiosulfate solution and dilutehydrochloric acid, as shown in Figure 1.
The reaction produced a precipitate, which made the mixture turn cloudy.
The student timed how long it took until she could no longer see the cross.
She calculated the rate of the reaction.
(a) The equation for the reaction is:
Na2S2O3(aq) + 2 HCl(aq) 2 NaCl(aq) + S(s) + SO2(g) + H2O(l)
Name the product that made the mixture go cloudy.
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(1)
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Page 14 of 73
(b) The student investigated the effect of changing the temperature of the sodium thiosulfatesolution on the rate of reaction.
She plotted her results on a graph, as shown in Figure 2.
Describe the trends shown in the student’s results.
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(2)
Page 15 of 73
(c) The student then investigated the effect of changing the concentration of sodium thiosulfatesolution on the rate of the reaction.
(i) Suggest two variables the student would need to control to make sure that herresults were valid.
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(2)
(ii) From this investigation the student correctly concluded:
‘As the concentration of sodium thiosulfate solution doubles, the rate of reactiondoubles.’
Explain the student’s conclusion in terms of particles.
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(3)
(Total 8 marks)
Page 16 of 73
A student investigated the rate of reaction between calcium carbonate (marble chips) andhydrochloric acid.
The student used the apparatus shown in Figure 1.
The student:• recorded the volume of gas collected every 5 seconds• repeated the experiment using hydrochloric acid at different temperatures.
The equation for the reaction is:
CaCO3(s) + 2 HCl(aq) CaCl2(aq) + H2O(l) + CO2(g)
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Page 17 of 73
(a) The student plotted results for the hydrochloric acid at 20 °C and 40 °C on a graph.
Figure 2 shows the student’s graph.
Use information from Figure 2 to answer these questions.
(i) State one conclusion the student could make about the effect of temperature on therate of the reaction.
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(1)
(ii) Give one reason why the student could make this conclusion.
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(1)
(iii) For the hydrochloric acid at 60 °C the student had collected 30 cm3 after 15 seconds.
Calculate the average rate of reaction from 0 to 15 seconds.
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Rate of reaction = ____________________ cm3 per second
(1)
Page 18 of 73
(b) The student then investigated how the surface area of marble chips affected the rate ofreaction.
(i) Which two variables should the student keep constant?
Tick ( ) two boxes.
Amount of water in the trough
Concentration of acid
Mass of marble chips
Size of marble chips
Volume of measuring cylinder
(2)
(ii) Explain, in terms of particles and collisions, the effect that increasing the surface areaof the marble chips has on the rate of reaction.
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(2)
(c) Calcium carbonate is a catalyst for the industrial production of biodiesel.
Give one reason why using a catalyst reduces costs.
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(1)
(Total 8 marks)
Page 19 of 73
Hydrogen gas is produced by the reaction of methane and steam.
(a) The diagram represents a molecule of hydrogen.
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(i) What type of bond joins the atoms of hydrogen?
Tick (✔) one box.
Covalent
Metallic
Ionic
(1)
(ii) A catalyst is used in the reaction.
Draw a ring around the correct answer to complete the sentence.
A catalyst
increases the rate of reaction.
increases the temperature.
increases the yield of a reaction.
(1)
(b) The equation for the reaction of methane and steam is:
CH4(g) + H2O(g) CO(g) + 3H2(g)
(i) What is meant by the symbol ?
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(1)
Page 20 of 73
(ii) Lowering the pressure reduces the rate of reaction.
Explain why, in terms of particles.
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(2)
(iii) The graph shows the yield of hydrogen at different temperatures.
Temperature in °C
The forward reaction is endothermic.
How does the graph show that the forward reaction is endothermic?
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(1)
(iv) Why is a higher yield produced if the reaction is repeated at a lower pressure?
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(1)
Page 21 of 73
(c) In this question you will be assessed on using good English, organising information clearlyand using specialist terms where appropriate.
Car engines are being developed that use hydrogen gas as a fuel instead of petrol.
The table compares the two fuels.
Hydrogen Petrol
Energy 5700 kJ per litre 34 000 kJ per litre
State Gas Liquid
Equation for combustion 2H2 + O2 → 2H2O 2C8H18 + 25O2 → 16CO2 + 18H2O
How the fuel is obtained Most hydrogen is producedfrom coal, oil or natural gas.Hydrogen can be produced bythe electrolysis of water or thesolar decomposition of water.
Fractional distillation of crude oil.
Page 22 of 73
Use the information in the table and your knowledge of fuels to evaluate the use ofhydrogen instead of petrol as a fuel.
You should describe the advantages and disadvantages of using hydrogen instead ofpetrol.
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Extra space _________________________________________________________
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(6)
(Total 13 marks)
Page 23 of 73
Lead nitrate solution reacts with potassium iodide solution.
The reaction produces a solid.
Figure 1 shows the reaction occurring.
Figure 1
Lead Iodide By Der Kreole (own work) (CC-BY-3.0) via Wikimedia Commons
(a) (i) Give the name of this type of reaction.
Tick (✓) one box.
Combustion
Neutralisation
Precipitation
(1)
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(ii) Write the missing state symbols in the chemical equation.
Pb(NO3)2(aq) + 2KI(___) PbI2(___) + 2KNO3(aq)
(2)
(iii) Complete the word equation for the reaction.
lead nitrate + _________ lead iodide + _________
(2)
Page 24 of 73
(iv) How is solid lead iodide separated from the solution?
Draw a ring around the correct answer.
Distillation Electrolysis Filtration
(1)
(b) A group of students investigated the movement of particles.
The students filled a container with water.
The students added a crystal of lead nitrate at position X and a crystal of potassium iodideat position Y, as shown in Figure 2.
Figure 2 – view from above
After 3 minutes solid lead iodide started to form at the position shown in Figure 3.
Figure 3 – view from above
(i) Tick (✓) the correct box to complete the sentence.
Lead ions and iodide ions move through the water by
diffusion.
evaporation.
neutralisation.
(1)
Page 25 of 73
(ii) What conclusion can you make about the speed of movement of lead ions comparedwith iodide ions?
Give a reason for your answer.
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(2)
(iii) The students repeated the experiment at a higher temperature.
The solid lead iodide formed after a shorter period of time.
Explain why, in terms of particles.
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(2)
(Total 11 marks)
Figure 1 represents a reaction in the production of sulfuric acid.
Figure 1
Oxygen
Sulfur dioxide Sulfur trioxide
(a) Complete and balance the equation for the reaction.
_____ SO2(g) + _____ (g) _____ SO3(g)
(2)
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Page 26 of 73
(b) The conditions can affect the rate of the reaction.
(i) The pressure of the reacting gases was increased.
State the effect of increasing the pressure on the rate of reaction.
Explain your answer in terms of particles.
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(3)
(ii) A catalyst is used for the reaction.
The gases pass through a layer containing pieces of the catalyst.
Figure 2 shows the shapes of pieces of catalyst.
Figure 2
A B
Suggest and explain why shape B is more effective as a catalyst than shape A.
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(2)
Page 27 of 73
(c) The reaction is carried out at a high temperature to provide the reactants with theactivation energy.
What is meant by the activation energy?
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(d) Sulfuric acid reacts with metals to produce salts.
(i) A student concluded that potassium would not be a suitable metal to react withsulfuric acid.
Explain why.
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(2)
(ii) A student reacted zinc metal with sulfuric acid to produce a salt and another product.
Complete the equation for this reaction.
Zn + H2SO4 _______________ + ______________
(2)
(iii) The student wanted to increase the rate of the reaction between the zinc and sulfuricacid.
State one way, other than using a catalyst, that the student could increase the rate ofthe reaction.
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(1)
(Total 13 marks)
Page 28 of 73
Carbon dioxide is produced when copper carbonate is heated.
A student investigated heating copper carbonate.The student used the apparatus to measure how long it took for carbon dioxide to beproduced.The student also noted what happened during each minute for three minutes.
(a) The student used changes to the limewater to measure how long it took for carbon dioxideto be produced.
Describe how.
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(2)
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Page 29 of 73
(b) The student wrote down her observations.
Time intervalin minutes
Observations
Between 0 and 1A slow release of gas bubbles.The limewater did not change.The solid in the test tube was green.
Between 1 and 2A fast release of gas bubbles.The limewater changed at 1 minute 10 seconds.
Between 2 and 3No release of gas bubbles.The solid in the test tube was black.
(i) Suggest the reason for the student’s observations between 0 and 1 minute.
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(2)
(ii) Explain the student’s observations between 1 and 2 minutes.
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(2)
(iii) Explain the student’s observations between 2 and 3 minutes.
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(2)
Page 30 of 73
Sulfur dioxide (SO2) is used to manufacture sulfuric acid.
(a) Explain why sulfur dioxide has a low boiling point.
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(3)
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(b) The equation shows one stage in the manufacture of sulfuric acid from sulfur dioxide.
2SO2(g) + O2(g) 2SO3 (g)
The reaction is exothermic in the forward direction.
Use Le Chatelier’s Principle to predict the effect of increasing the temperature on theamount of sulfur trioxide (SO3) produced at equilibrium.
Give a reason for your answer.
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(2)
(c) Use Le Chatelier’s Principle to predict the effect of increasing the pressure on the amountof sulfur trioxide (SO3) produced at equilibrium.
Give a reason for your answer.
(2)
(Total 7 marks)
Page 31 of 73
Ammonium nitrate (NH4NO3) is produced by reacting ammonia with nitric acid.
A student measured the mass of ammonium nitrate that dissolves in 100 cm3 of water at differenttemperatures.
The table below shows the student’s results.
Temperature in °C 0 20 40 60 80 100
Mass of ammonium nitrate in gthat dissolves in 100 cm3 water
119 190 286 321 630 1 024
(a) Use the table above to plot a graph of the solubility of ammonium nitrate on the figurebelow.
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Page 32 of 73
(4)
(b) At 20 °C, 190 g of ammonium nitrate dissolves in 100 cm3 of water.
Calculate the amount of ammonium nitrate (in moles) that dissolves in 1 dm3 of water at20 °C.
Relative atomic masses (Ar): H = 1; N = 14; O = 16
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Amount of dissolved ammonium nitrate = _________ mol
(3)
(c) Farmers use ammonium nitrate as a fertiliser.
Farmers want to slow down the rate at which ammonium nitrate fertiliser dissolves in thewater in the soil.
Suggest why they spread the fertiliser in the form of small beads instead of a fine powder.
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(2)
Page 33 of 73
(d) Ammonia is needed to make ammonium nitrate.
The reaction used to make ammonia is:
N2(g) + 3H2(g) 2NH3(g)
The forward reaction is exothermic.
At equilibrium, about 35% of the nitrogen and hydrogen are converted to ammonia at450 °C and 200 atmospheres pressure.
Explain the effects of increasing the temperature, or increasing the pressure, on theamount of ammonia produced at equilibrium.
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(4)
(Total 13 marks)
Some students were investigating the rate at which carbon dioxide gas is produced when metalcarbonates react with an acid.
One student reacted 1.00 g of calcium carbonate with 50 cm3, an excess, of dilute hydrochloricacid.
The apparatus used is shown in Diagram 1.
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Diagram 1
Dilute hydrochloric acid
Page 34 of 73
(a) Complete the two labels for the apparatus on the diagram.
(2)
(b) The student measured the volume of gas collected every 30 seconds.
The table shows the student’s results.
Time inseconds
Volume of carbon dioxidecollected in cm3
30 104
60
90 198
120 221
150 232
180 238
210 240
240 240
(i) Diagram 2 shows what the student saw at 60 seconds.
Diagram 2
What is the volume of gas collected?
Volume of gas = __________ cm3
(1)
Page 35 of 73
(ii) Why did the volume of gas stop changing after 210 seconds?
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(1)
(c) Another student placed a conical flask containing 1.00 g of a Group 1 carbonate (M2CO3)on a balance.
He then added 50 cm3, an excess, of dilute hydrochloric acid to the flask and measured themass of carbon dioxide given off.
The equation for the reaction is:
M2CO3 + 2HCl 2MCl + H2O + CO2
The final mass of carbon dioxide given off was 0.32 g.
(i) Calculate the amount, in moles, of carbon dioxide in 0.32 g carbon dioxide.
Relative atomic masses (Ar): C = 12; O = 16
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Moles of carbon dioxide = __________ moles
(2)
(ii) How many moles of the metal carbonate are needed to make this number of moles ofcarbon dioxide?
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Moles of metal carbonate = __________ moles
(1)
Page 36 of 73
(iii) The mass of metal carbonate used was 1.00 g.
Use this information, and your answer to part (c) (ii), to calculate the relative formulamass (Mr) of the metal carbonate.
If you could not answer part (c) (ii), use 0.00943 as the number of moles of metalcarbonate. This is not the answer to part (c) (ii).
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Relative formula mass (Mr) of metal carbonate = __________
(1)
(iv) Use your answer to part (c) (iii) to calculate the relative atomic mass (Ar) of the metalin the metal carbonate (M2CO3) and so identify the Group 1 metal in the metalcarbonate.
If you could not answer part (c) (iii), use 230 as the relative formula mass of themetal carbonate. This is not the answer to part (c) (iii).
To gain full marks, you must show your working.
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Relative atomic mass of metal is ____________________________________
Identity of metal _________________________________________________
(3)
Page 37 of 73
(d) Two other students repeated the experiment in part (c).
(i) When the first student did the experiment some acid sprayed out of the flask as themetal carbonate reacted.
Explain the effect this mistake would have on the calculated relative atomic mass ofthe metal.
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(3)
(ii) The second student used 100 cm3 of dilute hydrochloric acid instead of 50 cm3.
Explain the effect, if any, this mistake would have on the calculated relative atomicmass of the metal.
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(3)
(Total 17 marks)
Page 38 of 73
A company manufactures ethanol (C2H5OH).
The reaction for the process is:
C2H4(g) + H2O(g) C2H5OH(g) ΔH = −45 kJ per mole
The temperature and pressure can be changed to increase the yield of ethanol at equilibrium.
(a) Explain what is meant by equilibrium.
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(3)
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(b) (i) How would increasing the temperature change the yield of ethanol at equilibrium?
Give a reason for your answer.
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(2)
(ii) How would increasing the pressure change the yield of ethanol at equilibrium?
Give a reason for your answer.
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(2)
Page 39 of 73
(c) A catalyst is added to increase the rate of the reaction.
Explain how adding a catalyst increases the rate of a chemical reaction.
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(2)
(Total 9 marks)
A student investigated the reaction between magnesium metal and dilute hydrochloric acid.
The student placed 25 cm3 of dilute hydrochloric acid in a conical flask and set up the apparatusas shown in the diagram.
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The student:
• took the bung out of the flask and added a single piece of magnesium ribbon 8 cm long• put the bung back in the flask and started a stopwatch• recorded the volume of gas collected after 1 minute• repeated the experiment using different temperatures of acid.
Page 40 of 73
The student plotted his results on a graph.
Temperature of acid in °C
(a) Write the correct state symbols in the equation.
Choose from (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous.
Mg (….) + 2 HCl (….) MgCl2 (….) + H2 (…. )
(2)
(b) The diagram shows a gas syringe after 1 minute.
(i) What volume of gas has been collected in the gas syringe after 1 minute?
Volume = ____________ cm3
(1)
(ii) Use the graph to determine the temperature of the acid used in this experiment.
Temperature = ____________ °C
(1)
Page 41 of 73
(iii) Calculate the average rate of reaction, in cm3 of hydrogen made per second (cm3/s),for this experiment.
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Rate of reaction = ____________ cm3/s
(2)
(c) The student’s graph has been reprinted to help you answer this question.
Temperature of acid in °C
One of the results on the graph is anomalous.
(i) Draw a circle on the graph around the anomalous point.
(1)
Page 42 of 73
(ii) Suggest what may have happened to cause this anomalous result.
Explain your answer.
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(2)
(d) Explain how the student could improve the accuracy of the volume of gas recorded at eachtemperature.
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(3)
(e) The student then used the same apparatus to measure the volume of gas produced every10 seconds at 40 °C.
The student’s results are shown on the graph.
Page 43 of 73
Time in seconds
The rate at which the gas was produced got faster over the first 60 seconds.
The student’s teacher gave two possible explanations of why the reaction got faster.
Explanation 1There was a layer of magnesium oxide on the surface of the magnesium.The layer of magnesium oxide prevented the magnesium reacting with the acid.As the magnesium oxide reacted slowly with the acid, the magnesium was exposed to theacid and hydrogen gas was produced.
Explanation 2The reaction is exothermic, and so the temperature of the acid increased during thereaction.
(i) Describe further experimental work the student could do to see if Explanation 1 iscorrect.
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(2)
Page 44 of 73
(ii) Describe further experimental work the student could do to see if Explanation 2 iscorrect.
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(2)
(Total 16 marks)
This question is about gold (Au).
(a) An atom of gold is represented as:
Au
How many neutrons are in this atom of gold? ________________________
(1)
16
197
79
(b) Gold ions are used as a catalyst.
How does a gold atom (Au) become a gold ion (Au3+)?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(c) A gold catalyst can be used when carbon monoxide reacts with oxygen to make carbondioxide.
(i) Complete and balance the equation for this reaction.
__ CO + _______ → ___ CO2
(2)
Page 45 of 73
(ii) Carbon dioxide has a very low boiling point.
Explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(3)
(d) Gold is used as a catalyst in industrial processes. Gold is rare and increasingly expensive.
Suggest three reasons why gold is still used in industrial processes.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(Total 11 marks)
The equation for a reaction to produce hydrogen is:
CO(g) + H2O(g) CO2(g) + H2(g)
(a) Explain why changing the pressure does not affect the yield of hydrogen at equilibrium.
___________________________________________________________________
___________________________________________________________________
(1)
17
(b) Suggest why the best yield of hydrogen at equilibrium is obtained at low temperatures.
___________________________________________________________________
___________________________________________________________________
(1)
Page 46 of 73
(c) The temperature used in industry needs to be high enough for the reaction to take placequickly. Explain, in terms of particles, why the rate of reaction increases when thetemperature is increased.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(d) Scientists have developed catalysts which allow the reaction to take place quickly at lowertemperatures. How could this be good for the manufacturer and for the environment?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(Total 7 marks)
Methanol is a fuel that is used in some racing cars instead of petrol.
Methanol can be made from carbon monoxide and hydrogen. The equation for this reaction isshown below.
CO(g) + 2H2(g) CH3OH(g)
The forward reaction is exothermic.
18
(a) A high pressure (between 50 and 100 atmospheres) is used in this process.
Explain why the highest equilibrium yield of methanol is obtained at high pressure.
___________________________________________________________________
___________________________________________________________________
(1)
Page 47 of 73
(b) The temperature used in this process is about 250 °C.
It has been stated that, ‘the use of this temperature is a compromise between theequilibrium yield of product and the rate of reaction’.
Explain this statement.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(Total 4 marks)
Read the article and then answer the questions that follow.
Hydrogen fuel for cars?
Hydrogen is an excellent fuel. It can be made by the electrolysis of potassiumhydroxide solution.
Hydrogen gas can be stored under pressure in a cylinder but a leak of the gascould cause an explosion.
It has been found that lithium nitride can absorb and then release large volumesof hydrogen. A chemical reaction takes place between the hydrogen and thelithium nitride. The hydrogen is held in the resulting compounds by chemicalbonds.
The problem is that the rate at which hydrogen is absorbed and then releasedfrom normal sized particles of lithium nitride is slow.
Recently scientists have made ‘nanosized’ particles of lithium nitride. Theseparticles absorb hydrogen in the same way as normal sized lithium nitrideparticles. The ‘nanosized’ particles have the advantage that they absorb andrelease the hydrogen much faster when needed in the fuel cell.
It is hoped that ‘nanosized’ particles of lithium nitride may provide a safe methodof storing hydrogen in the future.
19
Page 48 of 73
(a) Hydrogen is produced at the negative electrode during the electrolysis of potassiumhydroxide solution.
(i) Why are hydrogen ions attracted to the negative electrode?
______________________________________________________________
______________________________________________________________
______________________________________________________________
(1)
(ii) Potassium ions are also attracted to the negative electrode.
Explain why hydrogen gas is formed but not potassium.
______________________________________________________________
______________________________________________________________
______________________________________________________________
(1)
(b) Lithium nitride is made by reacting lithium with nitrogen.
Balance the equation for this reaction.
_____ Li + N2 → _____ Li3N
(1)
(c) (i) The equation for the reaction of lithium nitride with hydrogen is:
Li3N + 2H2 LiNH2 + 2LiH
What feature of this reaction allows the hydrogen to be released?
______________________________________________________________
______________________________________________________________
(1)
Page 49 of 73
(ii) Hydrogen stored in a fuel tank filled with lithium nitride would be safer in an accidentthan a cylinder full of hydrogen.
Suggest and explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(d) Lithium nitride is an ionic compound which contains lithium ions (Li+) and nitride ions (N3–).
(i) The formation of a lithium ion from a lithium atom is an oxidation reaction.
Explain why.
______________________________________________________________
______________________________________________________________
(1)
(ii) The diagram shows the electronic structure of a nitrogen atom.
Complete the diagram below to show the electronic structure of a nitride ion (N3–).
(1)
(Total 8 marks)
Page 50 of 73
An airship caught fire when it was coming in to land in 1937. The airship was filled withhydrogen. A spark or flame ignited the hydrogen. The hydrogen reacted with oxygen in the air toproduce water.
20
(a) The equation for the reaction can be represented using structural formulae for thechemicals.
2 H – H + O = O → 2 H – O – H
Use the bond energies given in the table to help you to calculate the energy change for thisreaction.
Bond Bond energy in kJ per mole
H – H 436
O = O 498
O – H 464
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Energy change = __________________ kJ
(3)
(b) Explain, in terms of making and breaking bonds, why this reaction is exothermic.
___________________________________________________________________
___________________________________________________________________
(1)
Page 51 of 73
(c) Use the energy level diagram for this reaction to help you to answer these questions.
(i) The hydrogen did not burn until ignited by a spark or flame.
Explain why.
______________________________________________________________
______________________________________________________________
(1)
(ii) Platinum, a transition metal, causes hydrogen to ignite without using a spark orflame.
Explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(Total 7 marks)
Page 52 of 73
Mark schemes
(a) Level 3 (5–6 marks):A coherent method is described with relevant detail, which demonstrates a broadunderstanding of the relevant scientific techniques and procedures. The steps in themethod are logically ordered with the dependent and control variables correctly identified.The method would lead to the production of valid results.
Level 2 (3–4 marks):The bulk of a method is described with mostly relevant detail, which demonstrates areasonable understanding of the relevant scientific techniques and procedures. Themethod may not be in a completely logical sequence and may be missing some detail.
Level 1 (1–2 marks):Simple statements are made which demonstrate some understanding of some of therelevant scientific techniques and procedures. The response may lack a logical structureand would not lead to the production of valid results.
0 marks:No relevant content
Indicative content• remove bung and add magnesium• start stopclock / timer• measure volume of gas at fixed time intervals• repeat with different concentrations of acid• control volume of acid• control initial temperature of acid• control amount / mass / length / particle size of magnesium
6
1
(b) 6.5 cm3
1
(c) all points plotted correctly
allow 1 mark for 4 points plotted correctly2
best fit straight line drawn1
(d) when the concentration of acid increased the rate of reaction increased or vice versa
answer must use the terms ‘rate of reaction’ linked to‘concentration’
1
[11]
(a) products below reactants12
correct energy profile1
Page 53 of 73
activation energy correctly labelled1
energy given out correctly labelled1
(b) 31 (%)1
(c) the products would be above the reactants1
(d) catalysts increase rate of reaction
1 mark for each property
1 mark for each explanation
so products formed in less time
or
catalysts lower activation energy
explanation must be linked correctly to the property to gain the mark
so lowers energy requirements
or
catalysts not used up in the reaction
so only an initial outlay needed
or
only a small amount of catalyst needed
so small initial costmax. 4
(e) Protein1
(f) high temperatures1
extremes of pH1
(g) lactase acts as the lock, lactose is the key (substrate)1
lactase has an active site which will only fit lactose molecules1
so lactase will not work with other molecules1
[16]
Page 54 of 73
(a) (as concentration increases)
answers must refer to data from graph to gain full marks
relationship identified from the graph
eg the same volume of gas is collected in a shorter time or moregas is collected in the same time or reaction reaches completion ina shorter time
1
3
reference to relevant data to evidence relationship
eg 20 ml collected in 10 seconds at 0.5 mol / dm3 in 6.5 s at 1.0 mol/ dm3 and in 4 s at 2.0 mol / dm3
or
at 10 seconds volume collected is 20 cm3 with 0.5 mol / dm3, 30cm3 with 1.0 mol / dm3, 50 cm3 with 2.0 mol / dm3
or
total volume collected reaches maximum of 100ml in 20 seconds at2.0 mol / dm3 but takes twice as long at 1.0 mol / dm3 and at 0.5mol / dm3
1
(b) reactions occur when particles collide1
increasing concentration means there are more particles in the same volume1
so there are more collisions1
(c) leave for longer1
if gas continues to be produced student A is right1
or
repeat with more acid (1)
if more gas is produced student B is right (1)
[7]
(a) 6.1 circled on table (15 °C, test 1)14
(b) 1.8
do not allow 1.831
(c) 16 (minutes)
correct number extrapolated from curve1
Page 55 of 73
(d) 4.0 min – blue / black / purple1
7.0 min – yellow / orange / brown1
(e) The amylase solution had been prepared with water at 95 °C1
(f) Level 3 (5–6 marks):A clear and coherent method is described using logical steps and demonstrating a goodunderstanding of how to improve the validity of the method. The method would lead tothe production of valid results that would give rise to a more valid conclusion.
Level 2 (3–4 marks):The substantive content of a method is present and demonstrates reasonableunderstanding of how to improve the validity but may be missing some detail. The planmay not be in a completely logical sequence but leads towards the measurement ofrate of the reaction.
Level 1 (1–2 marks):Simple relevant statements made, which demonstrate limited understanding of how toimprove the experimental method. The response lacks logical structure and would notlead to the production of valid results or a more precise optimum temperature.
0 marks:No relevant content
Indicative content• conduct at a greater range of temperatures• use temperatures both above and below 40 °C• use smaller temperature intervals to get a more accurate optimum (eg go
up in 2 °C increments)• take samples at smaller time intervals to get a more accurate result for
‘time taken’• control the volume of starch used (eg 5 cm 3)• control the volume of the amylase solution (eg 1 cm 3)• control the temperature (eg using a water bath)• heat the two solutions separately before mixing• control the concentration of the starch solution• control the concentration of the amylase solution
6
[13]
Page 56 of 73
(a) sulfur / sulphur / S / S(s)1
(b) as the temperature increases, the rate of reaction increases
allow two correct values for rate quoted (from graph) at differenttemperatures
1
the rate of increase increases or there is an exponential relationship
accept the rate of reaction increases slowly (from 20 °C to 50 °C)then increases more rapidly for 2 marks
answer MUST be based on rate / speed of reaction1
5
(c) (i) any two from:• temperature (of the reactants)• concentration of hydrochloric acid• volume of hydrochloric acid• volume of sodium thiosulfate• the (size / darkness / thickness of the) cross• total volume of solution.
if no other marks gained, allow 1 mark for:
rate of stirring
OR
amount of hydrochloric acid / sodium thiosulfate
OR
volume of solution2
(ii) (because as the concentration increases) the number of particles per unitvolume increases or particles are closer together.
idea of more particles in a given space is required for the first mark.
ignore references to area.1
(therefore) the frequency of (successful) collisions increases
allow increased chance / probability of collisions
number of collisions increases is insufficient here.
must mention per unit time or frequency.
ignore speed of collisions.
if reference to space and time missing from M1 and M2 but they areotherwise correct, then award 1 mark.
1
so the number of particles (per unit volume) doubles or (the frequency of)collisions doubles.
students can score 2 marks for a qualitative explanation; the thirdmark is for a quantitative explanation.
1
[8]
Page 57 of 73
(a) (i) the higher the temperature, the greater the rateorat 40 °C rate is faster than at 20 °C
accept the higher the temperature, the faster the reaction1
(ii) 40 °C curve is steeper
accept the 40 °C line becomes horizontal sooner
accept at higher temperatures the reaction finishes sooner
accept reaction finishes sooner at 40 °C
accept at higher temperatures the gas is produced fasterorcorrect comparison of data from the graph
1
(iii) 21
6
(b) (i) Concentration of acidMass of marble chips
2
(ii) increases rate
incorrect reference to energy = max 11
(because of) more frequent collisions (between particles)
accept particles are more likely to collide
ignore more collisions
ignore more successful collisions1
(c) any one from:• increases rate of reaction• reduces energy required• lower temperature can be used• catalyst is not used up.
1
[8]
(a) (i) covalent17
(ii) increases the rate of reaction1
(b) (i) the reaction is reversible1
(ii) at lower pressure the molecules will be further apart1
Page 58 of 73
so there will be fewer collisions per unit time
accept frequency of collisions lower1
(iii) as the temperature increases, the yield of the reaction increases1
(iv) 2 molecules / volumes become 4 or more molecules / volumes of product thanreactant
1
(c) Marks awarded for this answer will be determined by the Quality of Communication(QoC) as well as the standard of the scientific response. Examiners should also referto the information on page 5, and apply a ‘best-fit’ approach to the marking.
0 marksNo relevant content
Level 1 (1 – 2 marks)Candidate has written about some basic points from the table but has not added anyextra knowledge. Candidate may have included advantages or disadvantages.
Level 2 (3 – 4 marks)Candidate has attempted an evaluation using points from the table and their ownknowledge. Candidate has included advantages and disadvantages.
Level 3 (5 – 6 marks)Candidate has given an evaluation that includes both advantages anddisadvantages. Candidate has clearly linked points from the table with their ownknowledge and uses appropriate scientific terminology.
examples of the points made in the response
Advantages of using hydrogen:
• its combustion only produces water• combustion of hydrogen does not produce carbon dioxide or does not contribute to
climate change• petrol requires much more oxygen to burn so partial combustion is possible
producing carbon monoxide• combustion of hydrogen does not produce any particulates or does not contribute to
global dimming• petrol comes from a non-renewable source or there are renewable ways of producing
hydrogen, eg electrolysis of water.
Disadvantages of using hydrogen:
• hydrogen has to be stored at high pressure or risk of explosion or larger volumeneeded for storage.
• much less energy produced from the combustion of hydrogen or need to refuel moreoften
• most methods of producing hydrogen need fossil fuels.6
[13]
Page 59 of 73
(a) (i) precipitation18
(ii) (aq) on left hand side1
(s) on right hand side1
(iii) potassium iodide1
potassium nitrate1
(iv) filtration1
(b) (i) diffusion1
(ii) iodide ions move / diffuse faster than lead ions or travel further in the same time
Must be a comparison
Accept converse1
because the lead iodide forms much closer to the lead nitrate (or X) than thepotassium iodide (or Y).
allow because iodide ions are smaller than lead ions
allow references to potassium iodide and lead nitrate1
(iii) the particles / ions move / diffuse faster
ignore which particles / ions the student refers to1
because they have more energy or will collide / meet sooner
ignore reference to frequency of collisions1
[11]
Page 60 of 73
(a) O2 in correct space1
correct balancing
accept multiples1
(b) (i) rate increases
incorrect reference to energy = max 2
ignore references to equilibrium1
because particles are closer together
accept because there are more particles (per unit volume)
allow particles have less space / room to move around1
so frequency of collisions increases
accept particles are more likely to collide
ignore more collisions
ignore more successful collisions1
(ii) has a greater surface area1
so the reaction is faster
accept so more frequent collisions1
(c) the (minimum) amount of energy (particles must have) to react or to start a reaction
accept the energy needed to break bonds
ignore references to heat1
(d) (i) (potassium is) too / very reactive
ignore potassium is a Group 1 / alkali metal1
so dangerous / violent reaction
accept hydrogen produced rapidly1
(ii) ZnSO4
accept products in either order
ignore names of substances1
H2
do not accept brackets or charges in the formulae1
(iii) any one from:
9
Page 61 of 73
• increase concentration (of sulfuric acid)• increase temperature or heat it• increase surface area of zinc
1
[13]
(a) time from when the heating is started until110
the limewater turns cloudy / milky1
(b) (i) the temperature was not high enough
accept the copper carbonate had not started to decompose / react
accept it takes time to heat up the copper carbonate1
the bubbles of gas were air
accept no carbon dioxide produced1
(ii) the copper carbonate was decomposing / reacting
accept the temperature was high enough to cause decomposition /a reaction
1
so carbon dioxide was produced
allow correct word / symbol equation1
(iii) copper oxide was produced
allow correct word / symbol equation1
because the copper carbonate had completely decomposed / reacted
ignore all of the carbon dioxide had been given off1
[8]
(a) small molecules111
with weak intermolecular forces1
(so) only a small amount of energy is needed to separate the molecules
any reference to bonds being weak or being broken negates thesecond and third mark unless they are stated to be intermolecularbonds or bonds between molecules
1
(b) decreases1
Page 62 of 73
because the equilibrium shifts in the endothermic direction
allow reverse reaction favoured if forward reaction is exothermic1
(c) increases1
because there are more molecules of gas on the left-hand side
or converse1
[7]
(a) x axis scale correct112
y axis scale correct1
all points plotted correctly
± ½ small square1
curve correct, omitting the anomalous point1
(b) relative formula mass of NH4NO3 = 14 + (4 × 1) + 14 + (3 × 16) = 801
mass of ammonium nitrate in 1 dm3 at 20 °C = 190 × 10 = 1 900 g1
number of moles of ammonium nitrate in 1 900 g = 1 900 / 80 = 23.75 mol1
(c) small beads would dissolve slower than fine powder1
because the surface area of the bead is less than fine powder1
(d) increasing the temperature at equilibrium will reduce the amount of ammonia produced1
because the reaction is exothermic1
increasing the pressure at equilibrium will increase the amount of ammonia produced1
because the equilibrium will shift towards the smaller number of molecules in the equation(which is ammonia)
1
[13]
Page 63 of 73
(a) left hand: (conical) flask
do not accept round bottomedflask or container which is not a flask
1
13
right hand: beaker / trough
accept plastic box1
(b) (i) 1571
(ii) all calcium carbonate used up or reaction stopped
do not accept all acid used up1
(c) (i) 0.007(272727…)
correct answer with or without working gains 2 marks
if answer incorrect, allow (0.32 / 44) for 1 mark2
(ii) 0.007(272727…)
allow ecf from (c)(i)1
(iii) (Mr = mass / moles = 1 / 0.00727…) = 137.5 or 138
allow ecf from (c)(ii)
if use 0.00943 moles then = 106
if use 0.007 allow 143 (142.857)1
(iv) (138) – 60 (= 78)
23 / 851
(78 / 2) = 391
potassium
sodium / rubidium
identity of metal ecf on Ar, but must be Group 1
If no working max 1 mark1
(d) (i) (relative atomic mass) would decrease1
because the mass lost greater1
so moles carbon dioxide larger or moles metal carbonate greater1
Page 64 of 73
(ii) no change1
because the acid (already) in excess1
so the amount carbon dioxide lost is the same1
[17]
(a) the forward and backward reactions occur
allow reversible1
14
at (exactly) the same rate1
in a closed system
allow therefore the concentrations / amounts of the reactants andproducts remain the same
1
(b) (i) increasing the temperature would lower the yield of ethanol or the (position of)equilibrium moves to the left
if student has stated that increasing the temperature increases theyield then award 0 marks
1
since the backwards reaction is endothermic or the forward reaction isexothermic
1
(ii) increasing the pressure would increase the yield of ethanol or the (position of)equilibrium moves to the right
if student has stated that increasing the pressure decreases theyield then award 0 marks
1
because the position (of equilibrium) moves in the direction of the lower numberof moles (of gas)
2 (moles / molecules / volumes / particles) on lhs / 1 (mole /molecule / volume / particle) on rhs
1
(c) (a catalyst) provides an alternative pathway1
Page 65 of 73
with lower activation energy
or
(a catalyst) lowers the activation energy (1)
so less energy is needed to react or more particles react (1)1
[9]
(a) (s) (aq) (aq) (g)
must be in this order
2 marks if all four correct
1 mark if 2 or 3 correct2
15
(b) (i) 55
ignore units1
(ii) 54
allow ecf from (b)(i)1
(iii) 0.92
correct answer with or without working gains 2 marks
ecf from volume in (b)(i)
accept 2 d.p. up to calculator value
if answer incorrect, allow rate = (b)(i) / 60 for 1 mark2
(c) (i) circle round point at (48,22)1
Page 66 of 73
(ii) problem (1) and explanation (1)
explanation must give lower volume of gas or slower reaction
ignore human error unless qualified
problem with bung
e.g. bung not placed in firmly / quickly enough
so gas lost
or
problem with reagent
e.g. acid was diluted or acid not replaced
so reaction slower
or
problem with temperature
e.g. temperature was lower than recorded temperature
so reaction slower
or
problem with measurement
e.g. length of magnesium less than 8 cm or timed for less than a minute
so less gas produced2
(d) repeat the experiment (several times)1
because anomalous results could be excluded1
and then the mean can be determined / calculated
accept suggestion of alteration to method, which is explained as towhy it would reduce the error, for 3 marks (e.g. place themagnesium in a container within the flask (1) so it can be tipped intothe acid once the bung is in place (1). This will prevent anomalousresults or gas loss (1))
ignore idea of more accurate gas syringeignore shorter time intervals
1
(e) (i) use clean magnesium or use magnesium without oxide coating1
Page 67 of 73
compare results1
(ii) either
measure the temperature of the acid before (adding magnesium)1
and after adding magnesium
or
place the conical flask in a water bath (at 40 °C) (1)
compare results (1)1
[16]
(a) 118116
(b) it loses / transfers electrons
it = Au / gold atom1
three electrons
sharing / covalency = max 1 mark1
(c) (i) O2
1
2 CO and 2 CO2
orcorrect balancing of equation from O
accept correct multiples / fractions throughout1
(ii) reference to incorrect bonding = 1 mark max
because carbon dioxide is simple molecular / small molecules1
there are intermolecular forces (between the molecules)
allow intermolecular bonds1
so a small amount of energy needed (to separate molecules) or (intermolecularforces) are weak
1
Page 68 of 73
(d) any three from:
• gold is the only catalyst for some reactions
• catalysts are not used up
• improves speed of reaction
reduces amount of energy or process needs low(er) temperature
if no mark awarded, allow catalyst reduce costs (of the process) for1 mark
• only small quantities (of catalyst) needed3
[11]
(a) same number of (gaseous) molecules / moles / volume on both sides ofthe equation
allow particles for molecules
do not accept atoms
ignore amount1
17
(b) (forward) reaction is exothermic
accept reverse answer1
(c) any three from:
• particles gain energy
• particles move faster
allow particles collide faster / quicker
ignore move more / vibrate more
• particles collide more or more collisions
• more of the collisions are successful ormore of the particles have the activation energy orparticles collide with more force / energy
3
Page 69 of 73
(d) any two from:
• more product (obtained in shorter time)
accept better yield (of product)
• less fuel needed
accept less energy / heat / electricity needed
or
lower fuel costs
ignore cheaper unqualified
• less pollution caused by burning fuels
or
less specified type of pollution caused by producing heat / burning fuels
allow correct specified pollutants caused by burning fossil fuels egCO2 / greenhouse gases or correct effect of burning fossil fuels egglobal warming
accept thermal / heat pollution
• using less fuel conserves resources
accept sustainable
accept fossil fuels are non-renewable2
[7]
(a) fewer product molecules than reactant molecules (owtte) or
accept forward reaction produces fewer molecules
accept left hand side for reactants and right hand side for products
3 reactant molecules and 1 productor 3 volumes of gas becomes 1 volume of gas
accept high pressure favours the side with fewer molecules
ignore references to reaction rate1
18
Page 70 of 73
(b) any three from:
• low temperature gives best yield
accept add heat as increased temperature or ‘less’ as poor yield
or high temperature gives poor yield
• because the reaction is exothermic
accept reverse argument if clearly expressed
• reaction too slow at low temperatureor reaction faster at high temperature
accept add heat and reaction goes faster
• temperature used gives a reasonable yieldat a fast rate / compromise explained
allow get less product but it takes less timefor 2 marks
3
[4]
(a) (i) any one from:
• they are positive / cations
• they are H +
• opposite charges attract
ignore atom1
19
(ii) potassium is more reactive (or reverse)
assume ‘it’ refers to hydrogen
allow potassium reacts with water
allow potassium is very reactive or most reactive metal / element
allow hydrogen gains electrons more easily / is reduced more easily
accept potassium is higher up the reactivity series1
(b) 6 and 2
accept correct multiples and fractions1
(c) (i) the reaction / it is reversible or a description of a reversible reaction
allow ‘it is an equilibrium’
allow reversible symbol drawn correctly
allow ‘the reverse / back reaction’1
Page 71 of 73
(ii) lithium nitride
assume that ‘it’ or if they do not specify means lithium nitride
assume lithium / lithium nitrate refers to lithium nitride
• hydrogen is bonded / held / absorbed / has formed acompound / reacted with lithium nitride
1
plus one of:
• does not explode / cause a fire
• is not free / less hydrogen
• is not under pressure
• does not leak
• is only released slowly1
• compound of hydrogen with lithium nitride / product is(more) stable / less reactive / less chance of a reaction
accept converse for hydrogen as below
assume that gas / hydrogen means gas in the cylinder
• hydrogen (in cylinder) / gas is not bonded / held absorbed / in a compound / reacted with lithium nitride
1
plus one of:
• can explode / cause a fire
• is free
• is under pressure
• can leak
• releases quickly1
(d) (i) loss of an electron or loses electrons
do not accept any ref. to oxygen1
(ii) full outer shell of 8 electrons on circle
need not be paired
can be ×, dot or e
do not accept if extra electrons added to inner shell1
[10]
Page 72 of 73
(a) (bonds broken) = 1370 (kJ)1
(bonds made) = 1856 (kJ)1
change in energy = (–) 486
ecfignore sign
correct answer with or without working = 3 marks1
20
(b) energy released from forming new bonds is greater than the energyneeded to break existing bonds
allow the energy needed to break bonds is less than the energyreleased in forming bonds
do not accept energy needed to form bonds1
(c) (i) energy barrier needs to be overcome
or
activation energy supplied / needed
allow energy needed to start reaction or energy needed to breakbonds
accept high activation energy1
(ii) lowers activation energy(*)
or
provides lower energy pathway / route(*)
(*)2 mark answers
allow provides alternative pathway or platinum / it is a catalyst for 1mark
2
[7]
Page 73 of 73
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