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Chemical analysis - Standard demand – Questions
Q1.The diagram shows a chromatogram for a food colouring.
(a) How does the chromatogram show that the food colouring is a mixture?
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(b) A student makes measurements for spot C.
The table shows the results.
Distance in mm
Distance moved by spot C 7
Distance moved by solvent 39
Calculate the Rf value for spot C.
Give your answer to 2 significant figures.
Use the results in the table.
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Rf value = ____________________(3)
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(c) Plan a chromatography experiment to investigate the colours in an ink.
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(Total 10 marks)
Q2.Chromatography can be used to find out what substances a drug contains.
The diagram shows a chromatogram for seven different drugs.
(a) Calculate the Rf value of drug G.
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Rf value = ____________________(4)
(b) Describe what the diagram shows about drug D.
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(c) Which substance is most soluble in the solvent used in this chromatogram?
Give a reason for your answer.
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(d) Explain the result for drug F.
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(Total 10 marks)
Q3.Rainwater is collected from the roofs of houses as shown in Figure 1.
Figure 1
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(a) The water in the storage tank is not potable.
What does potable mean?
Tick one box.
Contains dissolved substances
Pure
Safe to drink
Tastes nice
(1)
(b) Why should the water in the tank be filtered to make it potable?
Tick one box.
To kill microbes
To remove dissolved gases
To remove dissolved solids
To remove undissolved solids
(1)
(c) A gas which bleaches litmus paper can be added to the water to make it potable.
Name this gas and explain why it is added.
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(d) The storage tank is made from concrete reinforced with steel wire, as shown in Figure 2.
Figure 2.
Figure 3 shows how the distance between the steel wires affects the relative strength of the concrete.
Figure 3
Use values from Figure 3 to describe the relationship shown by the graph.
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(Total 6 marks)
Q4.Chromatography can be used to separate components of a mixture.
(a) A student used paper chromatography to analyse a black food colouring.
The student placed spots of known food colours, A, B, C, D and E, and the black food colouring on a sheet of chromatography paper.
The student set up the apparatus as shown in Diagram 1.
Diagram 1
The student made two errors in setting up the apparatus.Identify the two errors and describe the problem each error would cause.
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(4)
(b) A different student set up the apparatus without making any errors.
The chromatogram in Diagram 2 shows the student’s results.
Diagram 2
(i) What do the results tell you about the composition of the black food colouring?
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(ii) Use Diagram 2 to complete Table 1.
Table 1
Distance in mm
Distance from start line to solvent front ______________
Distance moved by food colour C ______________
(2)
(iii) Use your answers in part (b) (ii) to calculate the Rf value for food colour C.
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Rf value = ____________________(1)
(c) Table 2 gives the results of chromatography experiments that were carried out on some known food colours, using the same solvent as the students.
Table 2
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Name of food colour
Distance from start line to
solvent front in mm
Distance moved by food colour in
mmRf value
Ponceau 4R 62 59 0.95
Carmoisine 74 45 0.61
Fast red 67 27 0.40
Erythrosine 58 17 0.29
Which of the food colours in Table 2 could be food colour C from the chromatogram?
Give the reason for your answer.
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(d) Two types of chromatography are gas chromatography and paper chromatography.
Give one advantage of gas chromatography compared with paper chromatography.
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(Total 12 marks)
Q5.A student was trying to produce hydrogen gas.
Figure 1 shows the apparatus she used.
Figure 1
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(a) No gas was produced.
The student’s teacher said that this was because the substances in the flask did not react.
(i) Suggest why the substances in the flask did not react.
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(ii) Which two substances could the student have put in the flask to produce hydrogen safely?
Tick (✓) one box.
Gold and dilute hydrochloric acid
Potassium and dilute hydrochloric acid
Zinc and dilute hydrochloric acid
(1)
(b) Another student did produce hydrogen from two substances.
Figure 2 shows the apparatus the student used to collect and measure the volume of the hydrogen gas.
Figure 2
Give the name of the apparatus labelled X.
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(c) The student did the experiment four times. Her results are shown in the table below.
Experiment Volume of hydrogen collected in
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one minute in cm3
1 49
2 50
3 35
4 48
(i) One of the results is anomalous.
Which result is anomalous? Write your answer in the box.
Give a reason for your choice.
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(ii) Calculate the mean volume of hydrogen collected in one minute.
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Mean volume = ____________________ cm3
(2)
(iii) Give a reason why the experiment should be repeated several times.
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(d) A teacher collected two tubes full of hydrogen gas, as shown in Figure 3.
Figure 3
She tested tube A with a lighted splint as soon as she took the bung out.
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She tested tube B with a lighted splint a few seconds after taking the bung out.
(i) Suggest why tube B gave a much louder pop than tube A.
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(ii) Complete and balance the chemical equation for the reaction that takes place when the hydrogen reacts in this test.
H2 + O2 (2)
(Total 11 marks)
Q6.The label shows the ingredients in a drink called Cola.
ColaIngredients:
Carbonated water Sugar Colouring Phosphoric acid Flavouring Caffeine
(a) (i) The pH of carbonated water is 4.5.
The pH of Cola is 2.9.
Name the ingredient on the label that lowers the pH of Cola to 2.9.
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(ii) Which ion causes the pH to be 2.9?
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(b) A student investigated the food colouring in Cola and in a fruit drink using paper chromatography.
The chromatogram in the figure below shows the student’s results.
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Cola Fruit drink
(i) Complete the sentence.
The start line should be drawn with a ruler and ___________________ .
Give a reason for your answer.
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(ii) Suggest three conclusions you can make from the student’s results.
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(c) Caffeine can be separated from the other compounds in the drink by gas chromatography.
Why do different compounds separate in a gas chromatography column?
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(d) Caffeine is a stimulant.
Large amounts of caffeine can be harmful.
(i) Only one of the questions in the table can be answered by science alone.
Tick ( ) one question.
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Question Tick ( )
Should caffeine be an ingredient in drinks?
Is there caffeine in a certain brand of drink?
How much caffeine should people drink?
(1)
(ii) Give two reasons why the other questions cannot be answered by science alone.
Reason 1 ______________________________________________________
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Reason 2 ______________________________________________________
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(Total 11 marks)
Q7.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 dioxide to be produced.
Describe how.
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(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 2 A fast release of gas bubbles.The limewater changed at 1 minute 10 seconds.
Between 2 and 3 No 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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(ii) Explain the student’s observations between 1 and 2 minutes.
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(iii) Explain the student’s observations between 2 and 3 minutes.
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Q8.A student was investigating the reaction of lithium and water.
She added a few drops of universal indicator to water in a trough and added a piece of lithium.
The word equation for the reaction is:
lithium + water lithium hydroxide + hydrogen
(a) (i) The lithium floated on the water.
State two other observations that the student would see during the reaction.
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(ii) Balance the symbol equation for the reaction of lithium and water.
2 Li(s) + _____ H2O(l) _____ LiOH(aq) + H2(g)(2)
(iii) Describe a simple test and the result that would show the gas was hydrogen.
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(iv) All Group 1 metals have similar reactions with water.
State why, in terms of electronic structure.
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(b) Lithium and other Group 1 metals have different properties from the transition metals.
Tick (✔) two properties that are properties of Group 1 metals.
They react with oxygen.
They form coloured compounds.
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They are strong and hard.
They have low melting points.
(2)
(c) The electronic structure of a potassium atom is 2, 8, 8, 1
(i) Draw a diagram to show the electronic structure of a potassium ion.
Show the charge on the potassium ion.
(2)
(ii) Potassium is more reactive than sodium.
Explain why, in terms of electronic structure.
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(Total 13 marks)
Q9.Icing on cakes is tested to check that safe colours were used when they were made.
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By Megan Chromik [CC-BY-SA-2.0], via Wikimedia Commons
Paper chromatography is one method of testing which colours are in cake icing.
(a) The diagram shows an experiment a student did.
(i) Suggest why there is a lid on the container.
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(ii) The start line should be drawn in pencil not in ink.Suggest why.
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(1)
(b) The diagram shows the results of the paper chromatography experiment.
(i) How many different food colours were used in the colouring from the cake icing?
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(ii) Is the cake icing safe to eat?
Give a reason for your answer.
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(c) Gas chromatography linked to mass spectroscopy is an example of an instrumental method. This method was used on a mixture of solvents.
(i) Give two advantages of gas chromatography compared with paper chromatography.
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(ii) What does gas chromatography do to the mixture of solvents?
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(iii) What information does mass spectroscopy give?
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(Total 8 marks)
Q10.Read the article.
Problem food colouringsScientists say they have evidence that somefood colourings cause hyperactive behaviour inyoung children.
These food colourings are added to some sweets.
W, X, Y and Z are food colourings that may cause hyperactive behaviour in young children.
A scientist used chromatography to see if these food colourings were used in two sweets, S and P.
The results are shown on the chromatogram.
(a) Food colourings, such as W, X, Y and Z, are added to some sweets.
Suggest one reason why.
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(1)
(b) In chromatography, the Rf value =
Use the scale on the chromatogram to help you to answer this question.
Which food colouring, W, X, Y or Z, has an Rf value of 0.7?
(1)
(c) From the chromatogram, what conclusions can the scientist make about the colourings in sweets S and P?
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(Total 5 marks)
Q11.Some farmed salmon have a coloured additive in the food that they are given. This is a permitted additive that improves the colour of the fish meat.
A sample of the colour is extracted from a salmon.
Explain how paper chromatography could be used to confirm that this is the permitted additive.
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Q12.
(a) Suggest why it is important to be able to identify the colour additives in food.
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(b) A brown colour used in sweets was analysed using chromatography. The results were compared with those from E104 and E133.
What do the results tell you about the brown colour and its suitability for use in sweets?
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(c) Once all the unsuitable colours are removed, the company claims that its sweets are now ‘free from artificial colours’.
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Does this mean that the sweets contain no additives? Explain your answer.
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(Total 6 marks)
Q13.The electrolysis of sodium chloride solution is an important industrial process. The apparatus shown below can be used to show this electrolysis in the laboratory.
(a) Name gas A. _______________________________________________________(1)
(b) Chlorine is produced at the positive electrode. Describe and give the result of a chemical test to prove that the gas is chlorine.
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(c) Chloride ions move to the positive electrode. Explain why.
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(d) A small quantity of chlorine is added to drinking water. Explain why.
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(e) The solution around the negative electrode becomes alkaline. Name the ion which makes the solution alkaline.
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(Total 6 marks)
Q14.Hydrogen peroxide, H2O2, is often used as a bleach. It decomposes forming water and oxygen.
(a) (i) Write the balanced chemical equation for the decomposition of hydrogen peroxide.
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(ii) Give a test for oxygen.
Test _________________________________________________________
Result of test __________________________________________________
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(b) The rate of decomposition of hydrogen peroxide at room temperature is very slow. Manganese oxide is a catalyst which can be used to speed up the decomposition. Complete the sentence.
A catalyst is a substance which speeds up a chemical reaction. At the end of the
reaction, the catalyst is ________________________________________________(1)
(c) Two experiments were carried out to test if the amount of manganese oxide, MnO2 affected the rate at which the hydrogen peroxide decomposed.
(i) Complete the diagram to show how you could measure the volume of oxygen formed during the decomposition.
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(2)
(ii) The results are shown in the table.
Time in minutes 0 0.5 1 1.5 2 2.5 3 3.5
Volume of gas in cm3
using 0.25 g MnO20 29 55 77 98 116 132 144
Volume of gas in cm3
using 2.5 g MnO20 45 84 118 145 162 174 182
Draw a graph of these results. The graph for 0.25 g MnO2 has been drawn for you.
(3)
(iii) Explain why the slopes of the graphs become less steep during the reaction.
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(iv) The same volume and concentration of hydrogen peroxide solution was used for both experiments. What two other factors must be kept the same to make it a fair test?
1. ____________________________________________________________
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2. ____________________________________________________________
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(Total 15 marks)
Q15.Methane CH4 contains the elements carbon and hydrogen only. A student wanted to find out which new substances are produced when methane is burned. The student set up the apparatus shown below.
(a) Which gas in the air reacts with methane when it burns?
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(b) Name the liquid collected.
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(c) Name the gas which turns limewater milky.
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(d) When methane burns an exothermic reaction takes place. What is meant by an exothermic reaction?
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(Total 5 marks)
Q16.Scientists in the 16th century used the symbol shown in Figure 1 for gold.
Figure 1
Gold
The scientists thought platinum was made from gold and silver, so they used the symbol for gold in the symbol for platinum. The symbol for platinum is shown in Figure 2.
Figure 2
Platinum
(a) Gold and platinum are elements.
What is meant by the term element?
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(b) Why is it incorrect to represent platinum as shown in Figure 2?
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(c) Scientists now use a formula such as Ag2O to represent a substance.
What does the formula Ag2O tell you about this substance?
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(Total 4 marks)
Q17.Fire dancers use firesticks to make flame patterns.
One end of the firestick is soaked in kerosene.The kerosene is lit and burns with a yellow flame.
(a) Kerosene is a mixture of hydrocarbons.
Which elements are present in a hydrocarbon?
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(b) A student investigated the products formed when kerosene burned.
The diagram shows the apparatus the student used.
Describe and explain the observations you would expect the student to make.
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(Total 5 marks)
Q18.Many sea creatures have shells containing calcium carbonate.
(a) The seas are becoming more acidic.
Suggest and explain how acids affect the shells of sea creatures.
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(2)
(b) A student investigated the effect of heating calcium carbonate.
(i) The symbol equation for the chemical reaction that occurs when calcium carbonate is heated is:
CaCO3 → CaO + CO2
Complete the word equation for the reaction.
______________________ → ______________________ + carbon dioxide(1)
(ii) 50 g of CaCO3 produced 28 g of CaO.
What mass of CO2 was produced?
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____________________ g(1)
(iii) When carbon dioxide passed through the solution in test tube B, the solution became cloudy.
Name the solution.
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(Total 5 marks)
Q19.The picture shows a limestone quarry.
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By Thomas Bjørkan (Own work) [CC-BY-SA-3.0], via Wikimedia Commons
(a) Local residents were against the opening of a new limestone quarry. The quarry was estimated to have a 10-year operating period.
The quarry company gave reasons to show how the quarry could benefit local residents over the next 10 to 15 years.
Suggest one economic and one environmental reason the quarry company could give.
Economic reason ____________________________________________________
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Environmental reason _________________________________________________
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(b) What happens when limestone (calcium carbonate) is heated?
Include in your answer:
• the chemical names of the substances produced
• the name of the process.
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(c) (i) Lime is calcium oxide. Calcium oxide reacts with water to form calcium hydroxide, Ca(OH)2
Write the symbol equation for this reaction.
___________________ + ___________________ → ___________________(2)
(ii) Name the gas that a solution of calcium hydroxide in water is used to test for.
Give the result that you would see if the gas was present.
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(Total 8 marks)
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