Ch 5 Energy and Chemical Tc

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1. PHYSICAL AND CHEMICAL CHANGES

1. Energy is required to cause a chemical or physical change in matter. 2. A chemical change involves the formation of a new substance which is different in

composition and property from the original reactants. 3. A physical change only involves a change in form but no new substances are

formed. 2. HEAT CHANGE IN CHEMICAL REACTIONS

1. An exothermic reaction is one which releases heat to the environment. 2. An endothermic reaction is one that absorbed heat from the environment. 3. Exothermic and endothermic reactions bring about changes in temperature to the

reactants and products. 3. THE REACTIVITY SERIES OF METALS

METAL

REACTIVITY OF METAL WHEN REACTING WITH

Water Dilute acid Oxygen

Pottasium (K) Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Tin (Sn) Lead (Pb) Copper (Cu) Silver (Ag) Gold (Au)

React with cold water

React with dilute acid

Reactivity of Metals in decreasing order

React with hot water or steam

Do not react with cold water or steam

React with hot dilute acid

Do not react with dilute acid

1. Reactive metals such as sodium, calcium and pottasium reacts vigorously with water. 2. Less reactive metals such as zinc and iron react with steam. 3. Inactive metals such as gold and silver do not react with water or steam. 4. Most metals react with acids giving off hydrogen. 5. Most metals react with oxygen to form metallic oxides. 6. The reactivity series of metals consists of metals arranged in order of reactivity based

on its reactions with several substances.

4. APPLICATION OF REACTIVITY SERIES OF METALS 1. The extraction of metals is an industrial process of separating a pure metal from its

ore. In industry, metals are heated with carbon to separate them from the impurities in ore.

CHAPTER 5: ENERGY AND CHEMICAL CHANGES


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5. ELECTROLYSIS 1. Reactions that use electrical energy to dissociate a chemical compound is called

electrolysis. 2. A chemical compound that is capable of conducting an electric current in its molten or

aqueous form is known as an electrolyte. 3. The materials immersed in an electrolyte to enable electrical conductivity are called

electrodes. 4. The electrodes connected to the negative terminal of the battery or cell is termed the

anode. 5. The electrodes connected to the positive terminal of the battery or cell is termed the

cathode. 6. Anions and cations are charged particles that will be attracted to the anode and

cathode respectively during electrolysis. 7. In industry, electrolysis is widely used in the extraction of metals, purification of

metals and metal electroplating.

6. THE PRODUCTION OF ELECTRICAL ENERGY FROM CHEMICAL REACTIONS 1. Dry cell, lead acid accumulator, alkaline battery, silver oxide mercury batteries and

nickel cadmium batteries are some of the main sources of electrical energy.

7. CHEMICAL REACTIONS THAT OCCUR IN THE PRESENCE OF LIGHT 1. Some chemical reactions are initiated by light energy e.g. photosynthesis and

reaction of chemical photographic film. 2. Chemical should be stored in dark container to prevent them from reacting to light. 3. Sources of energy should be used carefully and prudently. Its use should not pollute

the environment or pose a danger to human health


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PAPER 1 1. Which of the following is a chemical change?

A. Ice melts C. Salt dissolves in water B. Milk turns sour D. Water evaporates from a pool 2. The diagram shows paper burning. What type of change is taking place? A. Colour change C. Physical change B. Rate of change D. Chemical change 3. Why is crystallization of copper (II) sulphate considered a physical change?

A. New substance is formed B. No new substance is formed C. More heat is absorbed during the reaction D. Chemical bonds between particles take place 4. Which of the following pairs of changes is true?

Physical change Chemical change

A Not reversible Reversible

B More energy needed Less energy needed

C No new substances formed New substances formed

D New particles are formed No formation of new particles

5. Which of the following is an endothermic reaction?

A. Haber Process B. Contact Process C. Reaction of acid and alkali D. Dissolving ammonium nitrate in water

6. Which of the following is true for endothermic reaction?

A. Heat is released to the surroundings B. The temperature of the solution decreases C. The pressure of the surroundings increases D. The products have less energy than the reactants


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7. Which of the following chemicals absorb heat from the surrounding when dissolved in water?

A. Sodium hydroxide C. Sulphuric acid

B. Ammonium chloride D. Hydrochloric acid 8. The table shows the result of dissolving one spatula of sodium hydroxide in

distilled water.

Type of solution Temperature( 0C)

Distilled water 29

Distilled water + Sodium hydroxide 31

Rises in temperature 2

What has caused the increase in temperature?

A. Oxidation took place B. Exothermic reaction took place C. Endothermic reaction took place D. Heat was absorbed from the surrounding area

9. The information shows a chemical reaction. Nitrogen + Hydrogen Ammonia + Heat Which of the following statements is true?

A. The process is called the Contact Process B. Heat was absorbed from the surrounding area C. The chemical reaction above is an exothermic reaction D. The chemical reaction above is an endothermic reaction

10. The diagram shows the heating of copper (II) carbonates What is solution X? A. Lime water C. Hydrochloric acid B. Distilled water D. Potassium manganate (IV)

Solution X


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11. Which of the following is the process of producing ammonia?

A. Haber process C. Reducing process B. Contact process D. Electrolysis process

12. Which of the following metals reacts more vigorously with oxygen? A. Zinc C. Aluminium B. Copper D. Magnesium 13. Which of the following is more reactive than carbon? A. Zinc C. Ferum B. Sodium D. Copper 14. What is the product when reactive metals reacts with water? A. Metallic oxide B. Salt and hydrogen gas C. Alkali solution and hydrogen gas D. Alkali solution and metallic oxide 15. Which of the following shows the difference between calcium and zinc?

A. Has a shiny surface B. Reacts with cold water C. Only reacts with steam D. Does not conduct electricity

16. What will happen to a zinc roof when acid rains fall on it?

A. Corrode B. Change its shape C. Become black in colour

D. Become stronger and harder 17. The diagram shows an apparatus used to investigate the reactivity of metals

toward oxygen.

Substance P


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What is substance P? A. Copper (II) oxide C. Sodium hydroxide B. Ammonium chloride D. Potassium manganate(VII)

18. The diagram shows a reaction of metal with water. Which of the following observation is correct?

A. The beaker becomes cool B. The sodium sinks in water C. Heat energy is released to the surroundings D. The sodium changes to become a black solid

19. The information below is about the reaction of metals L, M and N with water and steam.

Metal Observation

L Reacts vigorously with water.

M Does not react with cold water or steam.

N Reacts with steam but not with cold water.

Which of the following is the correct arrange of reactivity in ascending order? A. L,M,N C. N,M,L B. M,N,L D. M,L,N 20. The diagram shows gas P is collected in the experiment.

Water

Sodium


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What is P? A. Oxygen C. Chlorine B. Nitrogen D. Hydrogen

21. Aluminium + hydrochloric acid Aluminium chloride + Gas X Based on the above equation, what is gas X? A. Oxygen C. Helium B. Hydrogen D. Carbon dioxide 22. What is the product when magnesium reacts with oxygen?

A. Magnesium oxide C. Magnesium hydroxide B. Magnesium chloride D. Magnesium carbonate

23. The information shows the observations of metals P, Q and R when heated.

Metal Observation

P A bright flame spreads slowly.

Q A glow spreads slowly.

R Burns with shiny white flame.

S No change.

Which metal is the most reactive?

A. P C. R B. Q D. S 24. Which of the following metal oxides does not react with carbon? A. Zinc oxide C. Copper(II) oxide B. Ferum oxide D. Aluminium oxide 25. Which of the following statements about electroplating iron nail with silver is

correct? A. The iron nail is the anode B. The iron nail is the cathode C. The silver plate is the cathode D. The iron (II) nitrate solution is used as electrolyte 26. What is the element that is involved during the extraction of tin? A. Carbon C. Cryolite B. Iron granules D. Quicklime


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27. Why is Aluminium metal extracted from its ore by electrolysis and not through heating with carbon ?

A. Heating methods are complex B. Aluminium is more reactive than carbon C. Because source of carbon is hard to find D. The cost of extraction through electrolysis is cheaper

28. Which of the following equations represents the reaction that takes place in a blast furnace during the extraction of tin ore ? A. Tin + Carbon dioxide Tin oxide + Carbon B. Tin oxide + Carbon Tin + Carbon dioxide C. Tin carbonate Tin oxide + Carbon dioxide D. Tin oxide + Zinc Tin + Zinc oxide 29. Which of the following states of electrolyte could conduct electricity? A. Solid. B. Solid and molten C. Solid and aqueous D. Molten or aqueous 30. Which of the following is the application of electrolysis? A. Purification of metal B. Purification of non-metal C. Production of electrical energy D. Production of radioactive energy 31. The diagram shows an electroplating of an iron spoon.

What is solution R?

A. Chromium(III) nitrate C. Iron (II) sulphate B. Hydrochloric acid D. Silver nitrate

Solution R

Iron spoon

Chromium


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32. The diagram shows electrolysis process.

What is substance X?

A. Sugar solution C. Ethanol solution B. Glucose solution D. Sodium chloride solution 33. The diagram shows an electrolysis process.

What are the products of electrolysis at the anode and cathode?

Anode Cathode

A Oxygen Hydrogen

B Bromine Lead

C Lead Bromine

D Hydrogen Oxygen

Molten lead bromide

Carbon rod

Heat

Bulb

Switch

Substance X

Carbon rod

Bulb

Switch


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34. What is the purpose of cryolite in aluminium extraction? A. To purify the aluminium oxide B. To lowered the melting point of aluminium oxide C. To reduce the conductivity of aluminium oxide D. To extract aluminium from the aluminium oxide 35. The diagram shows how electrolysis is used to purify copper.

What is X and Y ? 36. Which of the following involves the conversion of chemical energy to

electrical energy?

A. Dry cell B. Electroplating C. Electrolysis of molten aluminium ore D. Reduction of a metallic ore by carbon

37. What type of battery is used in watches? A. Dry cell C. Silver oxide mercury B. Nickel cadmium D. Lead acid accumulator 38. What is the advantage of alkaline cell compared to dry cell? A. It is cheaper C. The size is smaller B. It is rechargeable D. It has a longer life span

X Y

A Carbon Pure copper

B Pure copper Impure copper

C Impure copper Pure copper

D Pure copper Carbon

Y X

Copper (II)

nitrate


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39. The diagram shows a simple cell.

Which electrodes and electrolyte could be used to cause the bulb to light up?

R S Electrolyte

A Copper Copper Copper(II) sulphate

B Carbon Carbon Sulphuric acid.

C Zinc Copper Ethanol

D Magnesium Copper Hydrochloric acid.

40. Which of the following is true for silver oxide mercury cell?

A. Small B. Cheap C. Heavy D. Rechargeable


Which of the following metals would be Q?

P Q

A Zinc Aluminium

B Zinc Iron

C Lead Iron

D Copper Magnesium


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42. Which of the following is the advantage of using lead acid accumulator?

A. Portable C. High voltage B. It is cheaper D. Not rechargeable


What is X and Y?

X Y

A Carbon rod Carbon rod

B Zinc plate Copper plate

C Copper plate Copper plate

D Glass rod Iron rod

44. Which of the following processes requires light to function? A. Rusting C. Respiration B. Burning D. Photosynthesis 45. The word equation below shows the decomposition reaction by light energy. Silver chloride Silver + Chlorine Which of the following changes of energy is correct?

A. Heat energy light energy B. Light energy chemical energy C. Heat energy chemical energy D. Chemical energy heat energy

46. Why does photography paper exposed to sunlight become black? A. Sunlight emits black light

B. Sunlight causes the formation of black pigments C. The layers of silver at photography paper is oxidized D. Silver bromide decomposes to silver and bromine


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47. What is the advantage of a dry cell compared to an acid-lead accumulator?

A. The voltage is higher B. It has longer life span. C. Its electrolyte does not spill D. It is long lasting as long as fuel is supplied 48. Which of the electric cells can be recycle? A. Dry cell B. Alkaline batteries C. Lead acid accumulators D. Silver oxide-mercury batteries 49. Why photosensitive chemical are stored in dark bottle? A. Sensitive to light B. Sensitive to heat C. React with water D. React with oxygen 50. What type of battery is used in a car? A. Alkaline battery B. Acid-lead battery C. Silver oxide battery D. Nickel-cadmium battery


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PAPER 2

SECTION A

1. The diagram shows an experiment of reaction between calcium and water. The volume of gas X collected from the reaction is shown in table I.

b) Based on table I, draw a graph to show the relationship at the total volume of gas X against time.

DIAGRAM 1

Volume of X (cm

3)

Time / s

40

60

80

20

120 30 602020

90 0 150

X

X

X

X


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a) What is the relationship between the volume of gas X and time in the first 90 second? ..

(1 mark)

b) State the hypothesis based on Table 1. .. ...

(1 mark) c) State the responding variable in this experiment.

(1 mark)

d) What is the total volume of gas X, which is collected in 90 second?

(1mark) e) Predict the volume of gas X, which is collected in 180 second

(1mark) 2. Diagram 2 shows an arrangement of apparatus to study the purification of metal.

Copper(ll)nitrate solution

DIAGRAM 2

+ -

As the time increases, the volume of gas X collected increases

The longer the time taken the higher the volume of gas X collected

The volume of gas X collected

71cm3

74cm3/ No change


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The experiment is repeated a few times with different quantities of electric current. The mass of cathode after 10 minutes are recorded in table 2.

Electric current (A)

0.3 0.6 0.9 1.2 1.5 1.8 2.1

Mass of cathode (g)

1.05 1.10 1.15 1.25 1.30 1.35

TABLE 2

(a) In diagram 2, mark the positive electrode and the negative electrode with the symbol (+) and (-).

(1 mark) (b) Draw a graph showing the mass of cathode versus the quantity of electric current.

c) From the graph, drawn, determine the mass of cathode when the quantity of electric current is 1.2A.

(1 mark)

d) What is the relationship between the quantity of electric current and the mass of cathode? (1 mark)

1.2

1.3

1.4

1.1

2.0 0.5 1.0 1.5 0 2.5

1.0

Quantity of Electric current (A)

Mass of cathode (g)

X

X

X

X

X

X

1.2g

The larger the quantity of electric current that flows, the higher

the mass of cathode.


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3. Diagram 3 shows an experiment done by a student.

DIAGRAM 3

Table 3 shows the result of the experiment.

Beaker Substance Initial

temperature Final

temperature

A Hydrochloric acid +

sodium chloride 29 0C 34 0C

B Water +

ammonium chloride 29 0C 25 0C

TABLE 3

(a) State the type of chemical reaction in both beakers. i. Beaker A. ii. Beaker B.

...... (2 marks)

(b) Give inference for your answer in (a).

.. ..

(1 mark)

Hydrochloric acid

Water

Beaker B Beaker A

Ammonium chloride

Sodium chloride

Thermometer

Exothermic reaction

Endothermic reaction

Heat is released in the reaction in beaker A while heat is absorbed in the reaction in beaker B


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(c) Name the variable involved in this experiment.

i. Manipulated variable.

ii. Constant variable. .

(2 marks)

4. Diagram 4 shows a simple cell for the production of electrical energy.

DIAGRAM 4 Table 4 shows the result of the experiment.

Experiment Pair of metals Voltmeter/V

I Zinc and copper 1.1

II Lead and copper 0.5

TABLE 4 (a) Based on experiment above, complete the voltmeter reading in Table 4. (2 marks) (b) Give your inference from the observation? ... (1 mark)

(c) State the variables in this experiment. i. Manipulated variable.

ii. Responding variable.

(2 marks)

(d) If copper plates are used for electrode A and B, predict the voltmeter reading. (1 mark)

Types of substances

Quantity of water

Experiment II Experiment I

An electric current is produced in both experiment

Pair of metals

Voltmeter reading

0 // zero // no voltmeter reading


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SECTION B 1. Diagram 5 shows a model of a simple cell.

DIAGRAM 5 a) What can be observed on the Galvanometer? . (1mark)

b) Give an inference to the observation in 1(a).

. (1 mark)

c) Write the energy, transformation that occurs in this experiment. . (1 mark) d) (i) What will happen if the copper plate is replaced with a carbon rod?

. (1mark)

Galvanometer

G

Copper plate

Vinegar solution

Zinc plate

The needle of the galvanometer deflects // galvanometer shows reading

Electric current is produce

Chemical energy Electrical energy

The needle of the galvanometer deflects


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2. Diagram 6 shows an experiment to study the reactivity of metals with oxygen. The metal is heated first before potassium manganate(VII) is heated. DIAGRAM 6

The observation of this experiment is recorded in Table 5.

Metal Observation

P Glow brightly

Q Glow dimly

R Burn brightly

TABLE 5 (a) Arrange the above metals in the decreasing order of reactivity with oxygen. .. (1 mark) (b) What is the function of potassium manganate (VII)? (1 mark) (c) Explain why the glass wool is placed in between the metals and the potassium

maganate(VII) .

... ... (1 mark)

(d) Explain why the metals are heated first before heating potassium manganate(VII).

.. ..

(1 mark)

metal

R, P, Q

To produce oxygen gas

To prevent potassium manganate (VII) from mixing with the metals

So that oxygen can react faster with hot metals


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3. Diagram 7 shows the apparatus to electroplate an iron ring.

DIAGRAM 7

(a) Give two reasons why iron ring need to be coated with silver. i. To prevent the ring from corrosion

ii. To make the ring looks more attractive

(2 marks) (b) Suggest a suitable electrolyte. Silver nitrate .. (1 mark)

(c) State the observation that occur at i. anode. The silver plate becomes thinner .. ii. cathode. Silvery metal deposited on the ring. . (2 marks)

Electrolyte

Iron ring Silver


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SECTION C 1. Study the statement below carefully.

A large amount of air bubbles is released when a magnesium strip is placed in hydrochloric acid but when a copper plate is placed in the same acid, no

changes are observed.

(a) Suggest a suitable hypothesis to investigate this statement. [1 mark] (b) Describe one experiment to test your hypothesis based on the following.

(i) Aim of experiment [1 mark] (ii) Variables [2 marks] (iii) List of apparatus [1 mark] (iv) Method [3 marks] (v) Tabulation of data [1 mark] (vi) Conclusion [1 mark]

ANSWER Hypothesis: The rate of reaction between magnesium and acid is higher than copper with acid or Magnesium has higher reactivity with acid than copper Aim: To study the rate of reaction of different metals with acid. Variable: Constant : Concentration of acid Manipulated : Type of metal Responding : Rate of reaction with acid Apparatus and materials: magnesium strip, copper plate, hydrochloric acid, boiling tube, cork stopper, delivery tube, water container, Bunsen burner, wooden tong. Method: -

5 cm3 of hydrochloric acid is poured into the boiling tube

3 cm long magnesium strip is put into the acid

The gas released is tested with a lighted wooden splinter

The experiment is repeated using copper

All observation are recorded in the table

Tabulation of data:

Metals Rate of reaction with acid

Magnesium

Copper

Conclusion: Different metals react with acid at the different rate


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2. (a) State one method used to purify a piece of impure copper. Explain the method. [4 marks]

(b) A man found a strange substance and after examines he confirmed that substance is a metal ore. . He heat the substance with carbon to purified it but no reaction occurs. Explain how the substance can be extracted from the metal ore.

Your answers should include the following. (i) Identify the problem

(ii) Clarification of the problem (iii) Solving methods (iv) Explain the method using [6 marks]

ANSWER

The diagram shows how electrolysis is used to purify copper

The anode is made of impure copper

The cathode is made of pure copper

The electrolyte used is copper (II) sulphate solution

Switch turns on.

A

Impure copper Pure copper

Copper (II) sulphate solution


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b)

Identify the problem : To extract metal from bauxite/ metal ore

Clarification of the problem: The metal ore does not reacts with carbon.

Solving methods: Use electrolysis

Explain the method using:

1. Set up the apparatus as shown in the diagram 2. Heat the crucible until the metal ore and cryolite melts. 3. Turn on switch to start the electrolysis process 4. Observe the graphite electrodes and ammeter 5. Record the observation

3. (a) Diagram 8 shows the formation of white fumes when ammonia gas and hydrogen gas are mixed. DIAGRAM 8

State four reasons why the reaction above is considered as a chemical change. [4 marks]

AA

Metal ore + cryolite

Graphite


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(b) Diagram 9 shows the physical changes that happen to two different substances.

DIAGRAM 9

Study the activities above carefully. Build a concept regarding the physical changes. Explain your answer based on the following.

(i) Identify the information [1 mark] (ii) Identify two common features [2 marks] (iii) Relate the common features with the physical changes to

build an initial concept [1 mark] (iv) State one example of physical change and one non-examples [1 mark]

(v) State the actual concept of physical change [1 mark] ANSWER a)

New substances are formed

Involving a change of heat energy

The new substance will have different chemical properties and composition

Difficult to reverse

Zinc nitrate solution

Soap solution

Soap powder

Zinc nitrate

Water

Water


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b) (i) Identify the information

Soap powder form bubble in water

Zinc nitrate powder formed zinc nitrate solution

(ii) Identify two common features

The state of the substance change

New substance are not formed

(iv) Relate the common features with the physical changes to build an initial concept

The process where state of the substance changes but new substance is not formed is a physical change

(iv) State one example of physical change and one non-examples

Example: The melting of ice/freezing of water

Non-example: Burning of paper (v) State the actual concept of physical change

The physical change is a process involving a change of state of matter and does not produce a new substance

Ch 5 Energy and Chemical Tc

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Transcript of Ch 5 Energy and Chemical Tc