Further Exercises

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For Page 8

A1	Explain the difference between catalytic cracking and steam (or thermal) cracking. Give equations to illustrate. What is the main purpose of each process?
A2	(a)	Write an equation using molecular formulae for the combustion of pentane.
	(b)	Write an equation for another common reaction that pentane undergoes. Name the type of reaction.
A3	When propane reacts with chlorine in the presence of u.v. light, a great variety of compounds is formed.
	(a)	How many monosubstituted compounds can be formed? Draw their structures.
	(b)	Write a balanced equation for the formation of one of these.
	(c)	How many disubstituted compounds can be formed? Draw their structures.

For pages 10-11

B1	Write equations using structural formulae for the reaction of 2-pentene with
	(a)	hydrogen (with a nickel catalyst)	(d)	hydrogen chloride
	(b)	bromine in a non-aqueous solvent	(e)	water (with sulfuric acid catalyst)
	(c)	bromine water (bromine dissolved in water)
	Name the compounds formed in (a), (d) and (e).
B2	In school laboratories to illustrate the test for distinguishing between alkanes and alkenes teachers commonly use hexane and hexene. Why are butane and butene not used? What is the test?

For pages 14 and 19

C1	Write an equation for the polymerisation of ethylene. What is the chemical difference between low density and high density polyethylene? Briefly describe the industrial processes for making these two products.
C2	Which of the following compounds would you expect to be able to form an addition polymer? CH₂=CHBr, CHCl=CHCl, CH₃–CH₂Cl, CH₃–CH₂–CH₂–CN, CH₃–CH=CHF, HO–CH₂–CH₂–OH For those that do, draw a segment of the polymer it would form.
C3	For four common addition polymers draw up a table showing a major use for each and the property that makes it particularly suited for that use.

For pages 21-22

(There are no exercises labelled D)
E1	The common nylon, called nylon-66, is made from What small molecule is eliminated when these molecules polymerise? Draw a segment of the polymer that forms; include at least two of each monomer units. Draw the structure of nylon-6 (page 20) under the structure of this nylon-66 and point out the similarities and differences between them.
E2	Kevlar is a very tough polymer; it is used for bullet-proof vests and sails for racing yachts. It is made from H₂N–C₆H₄–NH₂ and HOOC–C₆H₄–COOH where C₆H₄ is a benzene ring (the same ring that is present in styrene and polyester or PET). Draw the structure of a segment of Kevlar. To which class of compound does it belong?
E3	Silicones are polymers containing Si, O, C and H. They are used as water-proofing agents, breast implants, car polishes and synthetic rubber. The simplest silicone is made from (CH₃)₂Si(OH)₂ (four groups attached to a central Si atom). Draw the structural formula of this compound. Is polymerisation of this compound addition or condensation polymerisation? Draw a structure for a segment of the polymer to justify your choice. Polymerisation of (CH₃)₂Si(OH)₂leads to a linear-chain polymer. Show how use of some CH₃–Si(OH)₃ in the starting material would lead to chain branching.

After studying Section 1.13

E4	Give two (current or future) problems associated with the use of present-day synthetic polymers. Describe one recent development that has considerable potential for overcoming these problems. Include any relevant chemical structure.
E5	Explain how the structure of cellulose is derived from that of glucose. Include some form of chemical structure for cellulose. What is the 'stumbling block' in using cellulose as a source of C₂ to C₄ chemicals that we currently get from crude oil?
E6	Name two products in every-day use that are made from cellulose. Give a common use for each.

For page 28

F1	(a)	Draw the structure of 2-pentanol.
	(b)	Name the compound
F2	How many compounds are there that could be named hexanol? Draw their structures and name them.
F3	The compounds pentane and 1-pentanol have boiling points 138^oC and 30^oC. Which boiling point belongs to which compound? Explain how you decided this.
F4	If you wanted to make a solution of each of the following substances, for which ones would you use ethanol and for which water? iodine, magnesium sulfate, perfume, a food colouring agent, sucrose.

For pages 32-33

G1	Describe the production of ethanol from plant material. Give sufficient detail to justify it being a four-mark question in an HSC exam.
G2	What mass of ethanol do you need to burn to boil enough water to make a cup of coffee? Assume that you need 250 g water of specific heat capacity 4.2 J K^–1 g^–1, that it needs to be heated from 20^oC to 100^oC, that the molar heat capacity of ethanol is 1360 kJ mol^–1, and that 50% of the heat is lost to the surroundings.
G3	Describe how you would experimentally determine the heat of combustion of 1-propanol. Include a list of the actual measurements that you would make and explain how you would calculate a value of the heat of combustion from them. Write an equation for the combustion of 1-propanol. Identify two sources of error in your experiment.
G4	Discuss the use of ethanol as a fuel for motor cars, including any environmental impacts of such use. Assume that this is a five-mark HSC exam question.

For pages 39-40

H1	(a)	What changes, if any, would you observe if
		(i)	a piece of clean shiny magnesium ribbon was dropped into a pale blue copper sulfate solution
		(ii)	a piece of silver wire was dipped into another sample of the above copper sulfate solution
		(iii)	a silvery granule of zinc was dropped into a clear lead nitrate solution.
	(b)	Write oxidation and reduction half equations and the complete equation for each of the reactions that occur in (a).
H2	In the following ionic compounds what is the oxidation state of
	(a)	the metal atom in (i) aluminium hydroxide (ii) lithium sulfate (iii) titanium dioxide, TiO₂
	(b)	the non-metal atom in (i) iron(III) oxide (ii) sodium fluoride (iii) magnesium nitride, Mg₃N₂.

For page 45

J1	A cell consists of a silver wire dipping into a silver nitrate solution with a salt bridge connecting this solution to a solution containing chlorine and sodium chloride; a piece of platinum wire dips into this solution. Sketch what this cell would look like. Measurements with a voltmeter show that the platinum wire is positive with respect to the silver wire. What electrode processes are occurring? Show the direction of electron flow in the external circuit. What migration of ions occurs (if any) as current flows? What is the overall cell reaction?
J2	Sketch a possible experimental arrangement for a galvanic cell which would correspond to each of the following:
	(a)	a Mg, Mg²⁺ electrode connected to a Ni, Ni²⁺ electrode
	(b)	a hydrogen electrode (page 57) connected to a Cu, Cu²⁺ electrode
	In these cells the positive electrodes are (a) the nickel wire (b) the copper wire. On each of your sketches indicate the reaction that occurs at each electrode when the electrodes are joined with a conducting wire. Show the direction of flow of electrons in the wire and show the direction of any ion migration that occurs in the cell. For each cell write the overall reaction.
J3	For each of the cells in exercises J1 and J2 which electrode is the anode and which the cathode?

For page 49

K1	(a)	Write the anode and cathode reactions for (i) the Leclanché dry cell and (ii) the alkaline cell.
	(b)	What are the oxidation states of the oxidised and reduced forms of the metals in these reactions?
	(c)	List three similarities and three differences between these two cells.
K2	Repeat exercise K1 with the silver oxide cell instead of the alkaline cell.
K3	(a)	One type of lithium battery used in cameras consists of a Li, Li⁺ (in non-aqueous solution) electrode connected with a potassium hydroxide paste to an electrode consisting of MnO₂ and Mn(OH)₃in contact with an inert conductor. Write equations for the half reactions that occur at the electrodes (the Li electrode is negative) and hence the overall reaction.
	(b)	Another type of lithium cell is used in heart pacemakers (implanted in the body). It is completely solid state and lasts about ten years. In this cell one electrode is lithium metal while the other is iodine dispersed in a conducting polymer; these electrodes are separated by crystalline lithium iodide. Again the lithium electrode is negative. Deduce the electrode reactions and hence the overall reaction.
	(c)	Why is it necessary to exclude water from these cells?

After studying Section 2.13

L1	Zinc reacts with silver nitrate solution to form metallic silver. Would it be possible to use this reaction to make a galvanic cell? If so explain how you would make such a cell. Include a diagram. Give the electrode reactions and the overall reaction and on your diagram show the flow of electrons in the external circuit. Would this cell be rechargeable? Why or why not?
L2	As the lead accumulator is discharged, the concentration of sulfuric acid decreases. Explain why. On the other hand, as the nickel-cadmium cell is discharged the concentration of hydroxide remains constant. Explain why. What, if any, effect do you expect the decreases or constancy of electrolyte concentration to have on cell voltage?
L3	Why is the silver oxide cell not rechargeable?

For pages 63-4

M1	Explain how you would measure the standard electrode potential of the Pb, Pb²⁺ electrode if you did not have a standard hydrogen electrode available (but did have some other metal, metal ion electrodes available).
M2	(a)	Calculate the standard EMF of the following reactions
		(i) Cu²⁺ + Cd(s) ® Cd²⁺ + Cu(s)
		(ii) 2Fe³⁺ + 2Br^– ® Br₂ + 2Fe²⁺
	(b)	What do your answers tell you about the directions in which these reactions go?
	(c)	Physically, what does the 'EMF of a reaction' mean?

M3	(a)	A cell consisted of a piece of copper wire dipping into a 1.00 mol/L copper nitrate solution which was connected by a salt bridge to a 1.00 mol/L chromium(III) sulfate solution into which dipped a piece of chromium. The cell had an EMF (voltage) of 1.08 V, the copper wire being positive. Knowing that the standard electrode potential of the Cu²⁺, Cu electrode is +0.34 V, calculate E^o for the chromium electrode.
	(b)	A cell consisted of a piece of platinum dipping into a solution containing both iodine and iodide at unit molarity connected by a salt bridge to a 1.00 mol/L solution of zinc sulfate into which dipped a zinc rod. The EMF of the cell was 1.30 V (platinum wire positive). Knowing that E^o for the zinc electrode is –0.76 V, calculate the electrode potential of the iodine, iodide electrode.
M4	Two galvanic cells were made as follows:
		(i)	A piece of platinum wire dipped into a solution that was 1.00 mol/L in each Fe²⁺ and Fe³⁺. A salt bridge connected this solution to another one which was 1.00 mol/L in lead nitrate and which had a strip of lead metal dipping into it.
		(ii)	A piece of silver wire dipped into a 1.00 mol/L silver nitrate solution which was connected by a salt bridge to another solution which was 1.00 mol/L in iron(II) sulfate; a strip of iron metal dipped into this.
	(a)	Calculate the standard EMFs of these cells.
	(b)	Write the chemical reactions that occur in these cells as they generate electricity.
	(c)	Draw a diagram for each cell. Include some form of external circuit (for example, light bulb or voltmeter) On your diagrams show the way electrons and ions flow through the cells and external circuits.

For pages 72-3

N1	How many protons, neutrons and electrons are there in the atom and ions represented by the following symbols (X, Y and Z are not chemical symbols):
	(a)	(b)	(c)

N2	Complete the following nuclear equations:
	(a)
	(b)
	(c)
	(d)

N3	Use the Periodic Table to decide which element is formed when each of the following undergoes alpha decay (a) thorium-234 (b) uranium-235 (c) lead-210? What element is formed when the following elements undergo beta decay: (d) thorium-234 (e) sodium-24 (f) iodine-131?
N4	Which of the following elements would you expect to be unstable? Why? (a) ²³²Th (b) ²⁰Ne (c) ⁴⁰Ca (d) ²⁷Mg (e) ³H

For page 76

P1	If plutonium-239 is bombarded with an alpha particle of sufficient energy for the two particles to stick together to form an atom, what element would it be? Write a nuclear equation for the reaction.
P2	One product from fission of uranium-235 is caesium-137. Write a possible nuclear equation for the formation of caesium-137. (More than one equation is possible, depending upon whether 1, 2 or 3 neutrons are produced.)

For page 85

Iodine-131 has a half-life of 8 days. What percentage of a sample of this isotope will be present after 40 days?

Sodium-24 is a radioactive isotope. The radioactivity of a particular sample of sodium-24 was measured in counts (emissions) per second at various times from the start of an experiment (taken as time zero). Results are given in the following table

Time (hours)	0	5	10	15	20	25	30
Counts per second	464	370	292	232	185	146	116

(a)

What is the half-life of sodium-24? Explain how you decided this.

(b)

How long after the start of the experiment will it be until the disintegration rate for this sample is 58 counts per second?

(c)

Sodium-24 decays by beta emission. Write an equation for this decay process.

Describe (in sufficient detail to justify four marks in an HSC exam) one practical application (medical or industrial) of the use of a radioisotope. Include an explanation of how the method works and of how the results are interpreted.

Answers to Further Exercises

See pages 6 and 7; catalytic cracking breaks big alkane molecules into two smaller ones (for example hexadecane, C₁₆H₃₄ into two C₈ molecules or a C₁₀ and a C₆) while steam cracking breaks alkane molecules into C₂ to C₄ molecules (for example C₁₁H₂₄ into ethylene, ethane and propene) The main purpose of catalytic cracking is to increase the yield of petrol from crude oil, petrol being the product in greatest demand; the main purpose of steam cracking is to produce feedstock (mainly ethylene and propene) for the petrochemical and plastics industries.
Cataltyic cracking:C₁₆H₃₄ ® C₈H₁₈ + C₈H₁₆ (octane and octene)
Steam cracking: C₁₁H₂₄ ® 3C₂H₄ + C₂H₆ + C₃H₆A great variety of reactions is possible: just make sure the formulae of the hydrocarbons are correct and that your equations are balanced.

(a)

C₅H₁₂(l) + 8O₂(g) ® 5CO₂(g) + 6H₂O(g)

(b)

C₅H₁₂(l) + Cl₂(g) (+ uv light) ® C₅H₁₁Cl(l) + HCl(g)
substitution reaction

(a) two

(b) CH₃–CH₂–CH₃(g) + Cl₂(g) (+ uv light) ® CH₃–CH₂–CH₂–Cl(g) + HCl(g)

(c) four

Names are (a) pentane (d) 3-chloropentane (e) 3-pentanol
Or if the bottom structures were used, (d) 2-chloropentane and (e) 2-pentanol.

Butane and butene are gases while hexane and hexene are liquids. Add a solution of bromine dropwise to the sample and shake it. If the brown colour of bromine disappears the sample is an alkene: if the colour persists the sample is an alkane.

See bottom of CCHSC page 12 for the equation.
High density has linear chains and is largely crystalline whereas low density has branched chains and is generally amorphous. See Fig 1.3 on page 13.
For low density use high pressure and high temperature (1000 atm 300^oC) and a peroxide initiator. For high density use moderate pressure and temperature (few atm, 60^oC) and a Ziegler-Natta catalyst (TiCl3 + a trialkyl aluminium compound (see page 13).

CH₂=CHBr, CHCl=CHCl,CH₃–CH=CHF

Polymer	Use	Property
polyethylene	wrapping film	relatively soft and flexible
poly(vinyl chloride)	drain pipes	fairly rigid (without plasticiser) and easily moulded into various shapes
polystyrene	handles for tools	very hard (because of large benzene ring side group)
polyacrylonitrile	fibres for clothing and furnishings	readily forms fibres (because of polar nature of CN group)

E1	HCl; In these structures –(CH₂)₅– means –CH₂–CH₂–CH₂–CH₂–CH₂– and similarly with the 4 and 6. Similarities: (1) both use the same amide (or peptide) –CO–NH– linkage (2) both have six C atoms between the NH groups (3) both are linear chains (no branching) Differences: (1) In nylon-6 the repeat C6 units are all identical, –(CH₂)₅–CO– whereas in nylon-66 alternate ones are different, –CO–(CH₂)₄–CO– and –(CH₂)₆– (2) the CO groups are always 6 atoms apart along the chain in nylon-6 while in nylon-66 they alternate between 4 and 8 atoms apart.
E2	It is a nylon or polyamide or just a condensation polymer.
E3	Condensation, because molecules of water are eliminated between pairs of OH groups (on adjacent (CH₃)₂Si(OH)₂ molecules) to form
E4	Depletion of raw materials (crude oil) (pages 18-19), lack of biodegradability (page 24). Biological synthesis of poly(b-hydroxyalkanoates) such as poly(b-hydroxybutanoate) – describe it with a structure (see pages 24-5)
E5	By glucose molecules joining together by elimination of molecules of water (see middle of page 20). The simplest structure for cellulose would be –O–C₆H₁₀O₄–O–C₆H₁₀O₄–O–C₆H₁₀O₄–O–C₆H₁₀O₄ Alternatively you could use one of the following: (There are two OH groups and four H atoms attached to each ring that are not shown in these diagrams.) The 'stumbling block' is breaking the cellulose into glucose. Glucose is easily converted to ethanol by fermentation (see page 23).
E6	Any two of rayon (textiles), cellophane (wrapping), cellulose acetate (overhead projector slides), cellulose nitrate (explosive), carboxymethyl cellulose (food thickener).
F1	(a)
	(b)	3-heptanol
F2	3; 1-hexanol, 2-hexanol, 3-hexanol
F3	pentane, 30^oC; 1-pentanol, 138^oC. Hydrogen bonding occurs in 1-pentanol so it has strong intermolecular forces and so has the higher boiling point. Pentane has only dispersion forces.
F4	ethanol: iodine, perfume, a food colouring. Could use either for sucrose.
G1	Describe fermentation and make sure you include at least four significant facts: an equation, mention yeast, conditions to use (blood temperature, exclusion of air), maximum concentration produced, distillation (see pages 28-30).
G2	5.7 g
G3	Burn 1-propanol in a small spirit burner and use the heat to warm up some water in a container held over the flame. See CCPC page 291-2. Measure the mass of burner plus propanol before and after the burning. Measure the mass of water used and measure its temperature before and after heating. See Box 10.1 on page 292 for the calculation. C₃H₇OH + 5O₂ ® 3CO₂ + 4H₂O
G4	See pages 30-31. You need at least five significant facts. Ethanol can be used as an additive to normal petrol (to about 20%) without any modification to the car engine, or with engine modification 95% ethanol can be used as a total replacement for ordinary petrol; this was tried in Brazil in the 1970s and 80s but was abandoned because of cost factors. You could include the equation for combustion of ethanol. The main reason for wanting to use ethanol is to reduce the present rapid rate of consumption of oil which is likely to run out within a few decades. The other reason is its possible reduced contribution to the enhanced greenhouse effect. Currently ethanol is more expensive than petrol even when it is made from wastes such as molasses from sugar cane and it is dearer still if crops are grown specifically for making ethanol Key environmental issues are contribution to easing (or aggravating) the greenhouse effect (depending on where the energy for the distillation comes from), disposal of wastes from the fermentation process and possible land degradation resulting from putting large areas of land under crops.

H1	(a)	(i)	he magnesium gets covered with brown copper while the blue copper sulfate solution becomes paler
		(ii)	no change
		(iii)	The zinc becomes covered with a black deposit of lead metal.
	(b)	(i)	Mg ® Mg²⁺ + 2e^–; Cu²⁺ + 2e^– ® Cu Mg(s) + Cu²⁺(aq) ® Mg²⁺(aq) + Cu(s)
		(ii)	no reaction (see relative positions of Cu and Ag in the Activity Series on page 36.)
		(iii)	Zn ® Zn²⁺ + 2e^–; Pb²⁺ + 2e^– ® Pb Zn(s) + Pb²⁺(aq) ® Zn²⁺(aq) + Pb(s)
H2	(a)	(i) +3 (ii) +1 (iii) +4
	(b)	(i) –2 (ii) –1 (iii) –3

J1
J2	(a)	Diagram similar to the one in answer J1 with Mg and Mg²⁺ replacing Ag and Ag⁺ and with Ni replacing Pt and Ni²⁺ replacing Cl₂, Cl^–. Electron and ion flow is as in J1. Electrode reactions are Mg ® Mg²⁺ + 2e^– and Ni²⁺ + 2e^– ® Ni Overall reaction: Mg(s) + Ni²⁺(aq) ® Mg²⁺(aq) + Ni(s)
	(b)	Diagram as in the left-hand one of Fig 2.12 on CCHSC page 57 with Cu and Cu²⁺ replacing Zn and Zn²⁺. In the external circuit electrons flow from the Pt wire to the copper. Positive ions flow from the left-hand beaker to the right-hand one while negative ions flow from right to left.
J3	Anode: in J1 the silver electrode; in J2(a) the magnesium electode; in J2(b) the hydrogen electrode
K1	(a)	(i) Zn + 2MnO₂ + 2NH₄⁺ + 2H₂O ® Zn²⁺ + 2Mn(OH)₃ + 2NH₃(ii) Zn + 2MnO₂ + 3H₂O ® ZnO + 2Mn(OH)₃
	(b)	In both cells: +2 and ) for zinc, +4 and +3 for Mn
	(c)	Similarities: (i) The same metals undergo the same changes in oxidation state (or essentially the same reaction in both cells) (ii) generally made to look similar and to be interchangeable (iii) both are non-rechargeable. Differences: Any three of (i) The electrolyte paste in the Leclanché cell is slightly acidic (NH₄Cl) whereas in the alkaline cell it is highly basic (alkaline) (ii) the alkaline cell can deliver much higher currents (iii) The alkaline cell can deliver more total electricity from a cell of the same size (iv) Alkaline cells are more expensive (v) Alkaline cells can cause more damage if they leak.
K2	(a)	(i) Zn + 2MnO₂ + 2NH₄⁺ + 2H₂O ® Zn²⁺ + 2Mn(OH)₃ + 2NH₃(ii) Zn + Ag₂O ® ZnO + 2Ag
	(b)	In the Leclanché cell:+2 and 0 for Zn and +4 and +3 for Mn In the silver oxide cell: +2 and 0 for Zn and +1 and 0 for Ag.
	(c)	Similarities: (i) Basically the same anode reaction (oxidation of Zn) (ii) both are non-rechargeable (iii) Neither is able to deliver high currents. Differences: Any three of (i) They have very different cathode reactions – reduction of Mn in one, reduction of silver in the other (ii) Silver oxide cells are more easily made very small (iii) they can deliver more total electricity for a given size (iv) are more expensive and (v) have a longer shelf life.
K3	(a)	Li ® Li⁺ + e^–; MnO₂ + 2H₂O + e^– ® Mn(OH)₃ + OH^– Overall: Li + MnO₂ + 2H₂O ® Li⁺ + Mn(OH)₃ + OH^–
	(b)	Li ® Li⁺ + e^–; I₂ + 2e^– ® 2I^– Overall: 2Li + I₂ ® 2Li⁺ + 2I^–
	(c)	Because Li reacts with water (forming H₂ and LiOH)

L1	Yes; set up a cell similar to the right-hand one of Figure 2.4 on page 44 of CCHSC with a silver wire and silver nitrate solution replacing the copper rod and copper sulfate solution. Zn ® Zn²⁺ + 2e^–; Ag⁺ + e^– ® Ag; Zn(s) + 2Ag⁺(aq) ® Zn²⁺(aq) + 2Ag(s) Electrons would flow out of the zinc rod through the external circuit and into the silver wire. No, because as you tried to recharge it (by connecting a voltage source to the cell with the voltage source's negative terminal connected to the zinc) hydrogen ions or water would be reduced to H₂ in preference to Zn²⁺ being reduced back to Zn (note the relative positions of Zn and H in the Activity Series).
L2	Because the overall cell reaction uses it up; adding the two electrode reactions from near the bottom of page 55 gives the overall reaction Pb(s) + PbO₂(s) + 4H⁺(aq) + 2SO₄^2–(aq) ® 2PbSO₄(s) + 2H₂O(l) Because the overall cell reaction does not consume hydroxide; adding the two electrode reactions near the bottom of page 54 gives the overall reaction Cd(s) + NiO₂(s) + 2H₂O(l) ® Cd(OH)₂(s) + Ni(OH)₂(s) In the nickel-cadmium cell, because the electrolyte concentration remains constant, the cell voltage remains constant (until one of the reactants is nearly all consumed then it falls dramatically to zero). In the lead accumulator as the concentration of sulfuric acid decreases the cell voltage drops, because cell voltage depends upon concentration of the species involved in the cell reactions; as the concentrations of reactants decrease or of products increase the voltage drops.
L3	Because the anode reaction, Zn ® Zn²⁺ + 2e^–(or its alkaline equivalent, Zn + 2OH^– ® ZnO + H₂O) is not easily reversed by applying a voltage in the opposite direction: water is reduced to H₂ instead.
M1	Set up a cell using the Pb, Pb²⁺ electrode and a metal, metal ion electrode of which the standard electrode potential was known and measure its EMF. For example using a copper electrode (e^o = +0.34 V) set up the cell Pb \| Pb²⁺ \|\| Cu²⁺\| Cu and measure its voltage (0.47 V, Cu positive), then using Equation 2.12 from page 62 0.47 = 0.34 – e^o_Pbsoe^o_Pb = –0.13 V
M2	(a)	(i) +0.74 V (ii) –0.32 V
	(b)	(i) goes as written while (ii) goes in the reverse direction (Br₂ oxidises Fe²⁺)
	(c)	It is the EMF (voltage) of the galvanic cell in which the cell reaction is the given reaction: in the case of (i) it is the voltage of the cell Cd \| Cd²⁺ \|\| Cu²⁺ \| Cu
M3	(a)	–0.74 V
	(b)	+0.54 V
M4	(a)	(i) 0.90 V (Pt positive) (ii) 1.25 V (Ag positive)
	(b)	(i) Pb ® Pb²⁺ + 2e^–; Fe³⁺ + e^– ® Fe²⁺ (ii) Fe ® Fe²⁺ + 2e^–; Ag⁺ + e^– ® Ag
	(c)	(i) Diagram should look like the one in Answer 13 on page 533 with Fe²⁺, Fe³⁺ replacing I₂, I^– and with Pb, Pb²⁺ replacing Zn, Zn²⁺. (ii) Again like Answer 13 on page 533 with the right hand beaker having a silver wire and an Ag⁺ solution and the left hand one Fe metal and Fe²⁺ in solution.

N1	(a) 82 p, 122 n, 82 e (b) 29 p, 36 n, 27 e (c) 35 p, 45 n, 36 e
N2
N3	(a) Ra (b) Th (c) Hg (d) Pa (e) Mg (f) Xe
N4	(a) because its atomic number is greater than 83; (d) because its neutron to proton ratio is outside the zone of stability: it is in the blue region of Figure 3.1 on page 69, whereas the stable zone is the grey region; (e) same reason as (d)
P1	curium, Cm
P2	Alternatively you could have Rb-98 + 1n or Rb-96 + 3n
Q1	3.1%
Q2	(a)	15 h; this is the time required for the number of counts per second to drop to half – from 464 to 232, or from 370 to 185 or from 292 to 146 etc
	(b)	45 h
	(c)
Q3	Possible applications include (a) medical) (i) use of cobalt-60 for cancer treatment (ii) use of technetium-99m for medical diagnosis (b) industrial) (i) thickness gauges (ii) smoke detectors (iii) irradiation of medical supplies and/or food These are ones that are described in CCHSC pages 81-4. There are numerous others. For a four-mark HSC question you need to include at least four significant facts. Before deciding which application to describe mentally go over what you know about the method and make sure you have at least four key facts to include: otherwise consider do a different application. On all of the applications listed above there is enough information in CCHSC to score full marks. If short on facts, you could pad out your answer by including the nuclear equation for the disintegration involved or by mentioning some safety precautions, but make sure your 'story' holds together and is not just a collection of disjointed facts.