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Farr High School

NATIONAL 4 CHEMISTRY

Unit 1

Chemical Changes and Structure

Question Booklet

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Energy Changes of Chemical Reactions 1. What is meant by: (a) an exothermic reaction (b) an endothermic reaction. 2. A self-cooling can of beer has been developed. The beer is surrounded by an outer compartment containing a water gel. When the user activates a mechanism, the surrounding water quickly evaporates away, taking with it lots of heat energy from the liquid beer drink inside the actual can. Is this an example of an exothermic or an endothermic reaction? 3. Morven was investigating the reaction between magnesium and hydrochloric acid. As well as seeing bubbles of gas being released, she also noticed that the reaction mixture got hotter. Is the reaction exothermic or endothermic? Rates of Reaction 1. Marcy and Iain were investigating the time taken for 1.0 g of magnesium ribbon to react fully with 1.0 mol l-1 of hydrochloric acid at room temperature. They noted that the reaction took 130 seconds. Would the reaction be faster, slower or take the same time if the used: (a) 1.0 g of magnesium powder. (b) acid that has been stored in a fridge. (c) 0.5 mol l-1 acid. 2. Three experiments were set up as shown. Each experiment is carried out at room temperature and the mass of magnesium is the same in each case.

(a) State and explain any differences in the rate of reaction between: (i) Experiment A and B (ii) Experiment A and C (b) Explain any difference in the reaction rate if experiment A was repeated at 50 OC.

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3. What is meant by a catalyst? 4. Sammy and Jess investigated the effect of concentration on the rate of reaction between

magnesium and hydrochloric acid.

(a) State the volume of water the candidate should have used in (i) experiment 2 (ii) experiment 3 (b) Which experiment has the fastest rate of reaction.

5. Describe two ways to measure the rate of a reaction. You may wish to use diagrams to help with your description. 6. The graph below shows the rate of reaction between an excess of magnesium in a lump and 100cm3 of 1 mol l-1 hydrochloric acid at 20 oC. a) How long did the reaction take to finish? b) How much gas was produced in the first minute? c) What was the final volume of gas produced? d) Copy the graph and on it draw another line showing the rate of reaction between an excess of magnesium in a lump and 100cm3 of 1 mol/l hydrochloric acid at 40 oC.

Volume of

hydrochloric acid (cm3) Volume of

Water (cm3) Time/s

Experiment 1 20 0 50

Experiment 2 15 65

Experiment 3 10 90

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7. The following graph shows the change in mass against time when 5g of different marble samples were added to acid. (a) Which reaction was slowest? (b) Which graph represents the marble chips with the smaller particle size? (c) What is the total change in mass during each reaction? 8. A student carried out three experiments involving the reaction of magnesium with dilute acid. They measured the volume of hydrogen given off. The same mass of magnesium and volume of acid were used each time. A curve obtained for experiment 1 is drawn on the graph. Copy the above graph and draw 2 curves on the same axes to show the curves that would be obtained for experiments 2 and 3. Label each curve clearly.

Time (s)

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9. The graph below shows how the volume of hydrogen gas given off changed with time during a reaction between pieces of zinc and dilute sulphuric acid. a) At what time was the reaction complete? b) How much gas was produced between 0 and 20 seconds? c) What was the total volume of gas produced? 10. William and Sarah carried out an experiment to investigate the rate of reaction between calcium carbonate and dilute hydrochloric acid. They monitored the reaction by measuring the volume of gas produced over time. (a) Plot a graph of these results. (b) At what time after the start did the reaction finish? (c) What was the final volume of gas produced?

Time (s) Volume of gas (cm3)

0 0

10 20

20 40

30 56

40 70

50 82

60 90

70 96

80 100

90 102

100 102

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Atomic structure and bonding related to properties of materials

1. Copy out each sentence below choosing the correct word in the brackets to complete the sentence.

(a) Carbon, oxygen, iron and gold are all (metals/elements/compounds). (b) Things which contain only one type of atom are called (elements/compounds). (c) Compounds always contain (one/more than one) type of atom. (d) The chemical name for common salt is sodium chloride. There are (one/two/three)

parts to the chemical name. This means it is (an element/a compound).

2. Write the names of the elements which are found in the following compounds: (a) sodium chloride (b) aluminium oxide (c) sulphur dioxide (d) calcium sulphate (e) magnesium chlorate (d) iron nitrate 3. Look at the diagrams below.

(a) Which boxes show particle diagrams of elements? (b) Which boxes show particle diagrams of compounds? (c) Helium does not react with anything at all. Atoms of helium do not join up with any other atoms. Which diagram best represents helium? (d) Oxygen gas is in the form of particles which have the formula O2. Which two

diagrams show this arrangement? (e) Carbon dioxide has the formula CO2. Which diagram could represent carbon

dioxide? (f) Hydrogen atoms are smaller than any others. Which diagram could represent

water? Explain your answer.

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4. Atoms are made up of protons, neutrons and electrons. The diagram below shows a model of an atom. Copy the diagram and label parts (a), (b) and (c). 5. Tick the boxes after each statement to show whether it is true for protons, electrons or

neutrons.

6. The elements in the periodic table can be split into groups. Four of these groups are shown in the diagram below. Which group do the following elements belong to? a) sodium b) chlorine c) neon d) argon e) bromine f) iron g) potassium h) copper

protons electrons neutrons

Found in the nucleus of an atom

Found in ‘shells’ around the nucleus

Have no charge

Have a positive charge

Have a negative charge

Make up most of the mass of an atom

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7. Copy and complete the diagrams below to show the electron configurations of the atoms.

(Helium – 2 electrons, Oxygen – 8 electrons, Sulphur – 16 electrons, Potassium – 19 electrons)

8. Write down the valency of the following elements: a) sodium b) calcium c) helium d) carbon e) phosphorus f) silicon g) bromine h) argon i) nitrogen j) hydrogen k) oxygen l) chlorine m) magnesium n) fluorine o) aluminium 9. Write down the formula for the following compounds: a) sulphur dioxide b) nitrogen monoxide c) carbon tetrafluoride d) nitrogen trihydride e) sulphur trioxide f) dihydrogen dioxide g) dihydrogen oxide i) carbon tetrahydride

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10. Draw ‘dot and cross’ diagrams to show the outer electrons in the following covalent chemicals. (a) fluorine F2 (b) carbon dioxide CO2

(c) ammonia NH3 (d) methane CH4

11. Work out the chemical formula for the following ionic compounds: a) sodium chloride b) sodium oxide c) calcium oxide d) calcium chloride e) hydrogen chloride f) magnesium fluoride g) iron (III) oxide h) potassium nitride i) copper (II) chloride j) aluminium iodide k) magnesium oxide l) lithium nitride

12. Sodium atoms lose an electron to form positive ions (Na+). Chlorine atoms gain an electron to form chloride ions (Cl-). Use this idea to explain how sodium chloride crystals form.

13. Substance

Electrical conductor Solution in water

State at 25oC Solid State Liquid State

A yes yes insoluble liquid

B no yes soluble solid

C no no insoluble solid

D yes yes insoluble solid

From the table above, identify the substance which could be:- a) candle wax (C20H42) b) iron c) sodium chloride d) mercury 14. Look at the following information about potassium fluoride: Melting point 857 oC Boiling point 1502 oC Electrical conductor as a solid no Electrical conductor as a liquid or in solution yes Suggest the type of bonding present in potassium fluoride and give two pieces of evidence from the information above to support your answer.

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Calculating Formula Mass 15. Calculate the formula mass of the following chemicals: a) O2 b) MgCl2 c) NH3

d) SO2 e) Al2O3 f) iron (II) chloride g) calcium hydroxide h) ammonium chloride i) barium sulphate j) sodium nitrate k) aluminium chromate l) sulphur trioxide 16. For each of the reactions below, first write the word equation and then write the symbol equation. a) Hydrogen joins up with oxygen to make water. b) Iron metal and carbon dioxide are formed when iron (III) oxide is heated with carbon monoxide. c) In a car engine, petrol reacts with oxygen to form carbon dioxide and water vapour. d) The reaction of dilute hydrochloric acid with calcium carbonate produces calcium chloride, carbon dioxide and water. e) Ammonium sulphate is a fertiliser produced by the reaction of ammonia with sulphuric acid (hydrogen sulphate). f) Silver oxide breaks up when heated into its elements. g) Carbon powder burns in oxygen gas to form carbon dioxide gas. h) Zinc metal reacts with copper (II) sulphate solution to form copper metal and zinc (II) sulphate solution. i) Sodium hydroxide and hydrogen are produced when sodium reacts with water. j) Magnesium reacts with oxygen to form the compound of the elements.

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Acids and Bases 1. Are the following everyday examples of acids, alkalis or neutral chemicals? a) baking soda b) vinegar c) lemonade d) oven cleaner e) washing powder f) sugar 2. What do the following pieces of information tell you about the solutions? (a) Solution A turns universal indicator red. (b) Solution B has a pH of 8. (c) Solution C turns universal indicator purple. (d) Solution D has a pH of 7. 3. Do the following chemicals make acidic, alkaline or neutral solutions when they dissolve in water? (a) sodium chloride (b) carbon dioxide (c) hydrogen chloride (d) potassium hydroxide 4. Acid rain has a pH value between pH 5.5 and pH 2 – in some cases, the rain is as acidic as

vinegar! The acidity of the rain depends upon the amount of acidic gases dissolved in it. When acid rain reaches streams and lakes, it makes them acidic. This may kill the water life, including any fish. When acid rain falls on the ground, it soaks into the soil and reacts with the minerals in the soil. This may prevent plants from taking up minerals such as iron, zinc and magnesium which they need for healthy growth. As a result, plants and even well- established trees may die. When acid rain falls directly onto plants, it may damage new shoots and leaves. This also prevents the plant from growing. When acid rain falls on buildings and other structures it also causes damage. The acid rain reacts with any carbonates contained in the rocks used for building. Acid rain also corrodes metals such as iron, weakening bridges and other large structures. Choose one of the effects of acid rain listed above, and research it in more detail. Produce a three-minute talk to give your class about your findings.

5. Describe the environmental impact of carbon dioxide. 6. Give two reasons why acids may be added to food.

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7. Molly used a pH sensor to test different liquids. She dipped the probe of the sensor into each liquid and recorded the pH value in a table.

(a) Copy the table below and tick one box for each liquid

to show whether it is acidic, neutral or alkaline. One has been done for you.

liquid pH value acidic neutral alkaline

alcohol 7

dilute hydrochloric acid 2

Distilled water 7

vinegar 3

sodium hydroxide solution 11

(b) Between each test Molly dipped the probe into distilled water.

(i) Why did she do this? (ii) Which other liquid in the table could Molly use between tests to have the

same effect as distilled water?

(c) Molly put a piece of magnesium into a test-tube containing 20 cm3 of vinegar. She put another piece of magnesium into a test-tube containing 20 cm3 of dilute hydrochloric acid.

(i) Molly thought that magnesium

would react more vigorously with hydrochloric acid than with vinegar. What information in the table made Molly think this?

(ii) How would Molly be able to tell if a more vigorous reaction took place with hydrochloric acid than with vinegar?

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8. A scientist compared the acidity of four gases to see which gas might cause acid rain. She used four balloons to collect the gases. She then bubbled the gases, in turn, through a fresh sample of green, neutral, universal indicator solution.

Three of the gases caused the indicator to change colour.

The scientist added drops of alkali to the indicator until the indicator changed back to green. Her results are shown in the table below.

gases collected

change in colour of indicator

number of drops of alkali needed to change the indicator back to green

exhaust gases from a car

green to red 31

carbon dioxide green to red 160

air no change 0

human breath green to yellow 10

Use information in the table to answer part (a) and part (b) below.

(a) Which gas dissolved to form the most acidic solution? Explain your choice.

(b) Which gas formed a neutral solution? Explain your choice.

(c) What effect does an alkali have on an acid?

rubbertube

balloon containinggas

universal indicatorsolution

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9. A pupil used a sensor to record the change in pH of 10 cm3 of an acid solution when an alkali solution was added a little at a time. The concentrations of the alkali and acid solutions were fixed.

His results are shown in the table below.

volume of alkali added (cm3) pH of resulting mixture

0.0 5.0

2.0 5.0

4.0 5.0

6.0 5.5

8.0 6.0

10.0 7.0

12.0 8.0

14.0 8.5

16.0 9.0

18.0 9.0

20.0 9.0

(a) Use his results to draw a graph on a piece of graph paper.

Label the axes. Plot the points. Draw a smooth curve.

(b) Look at the graph. What would be the likely pH of the solution if the pupil

added a further 2 cm3 of alkali solution?

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10. Are pH balanced products really better for your skin? This is an exercise in planning. Many products now advertise the fact that they are ‘pH balanced’ or match our skin

pH of 5.5. Are these products really better for us, or is it just another advertising trick to get us to spend more money when a cheaper product would do the job just as well?

This is a scientific question, because it can be investigated using an experiment. It is not easy to plan this type of investigation because:

• it involves using people rather than test tubes or apparatus • the results would take a long time to gather • it is difficult to make it a fair test.

The following questions will help you to think about how you could set up a fair test.

You probably won’t be able to actually carry out the experiment, unless you have friends or family who are very patient!

a) Would it be fair to test the product on only one person? Why not? b) How many people would you need to involve in your test to make sure you had a

large enough sample? Would the age or gender be important? Suggest how you might choose a good scientific sample of people to be involved. c) Would everyone in the group try the pH balanced soap, or only some people? d) How do adverts try to show that hair treatments (e.g. dandruff shampoos)

work? Could you use this method for soaps? e) How would you tell if one soap was better than another? Would it be good

enough to rely on what the people using the soap told you? f) Would it matter if some people in the experiments thought that pH balanced products were better before they did the experiment? Explain your answer. g) When doctors try out a new medicine, they use a ‘blind test’. Some patients receive the medicine being tested and others get a similar pill or liquid without the drug in it (a ‘placebo’). The patient does not know if they are taking the real medicine or the placebo. Could you use this method for the soap experiment? Explain whether or not you think it might work. h) In a ‘double blind’ test, neither the doctor nor the patient knows which is the real medicine. Why do they set up a test like this? If you were doing the observations in the soap experiment, could you be trusted to be fair, or would it be better if you didn’t know which soap was which until after you had collected your results?

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11. Write word equations for the following reactions: a) Potassium hydroxide reacting with sulphuric acid.

b) Potassium hydroxide reacting with nitric acid.

c) Potassium hydroxide reacting with hydrochloric acid.

d) Calcium hydroxide reacting with hydrochloric acid.

e) Magnesium oxide reacting with hydrochloric acid.

f) Calcium hydroxide reacting with sulphuric acid.

12. Look at the labels from some products that use salts and then answer the questions below:

a) (i) Write down two uses for copper sulphate.

(ii) Copper sulphate can be made using a reaction between copper oxide and an acid. Which acid?

b) (i) Give two reasons for adding sodium chloride (common salt) to food.

(ii) Suggest an acid and an alkali that could be reacted together to make sodium chloride.

c) When photographic film is exposed to light, the salt on the film breaks down. What metal do you think is formed?