Answer Seminar Chemistry 2011 (Paper 2)

1. (a) i. proton, neutron and electronii. 2.1iii. 1

(b) i. Y and Zii. because Y and Z has same proton number but different nucleon

number//has same number of protons but different number of neutrons

(c) Iii. Because the energy absorb is used to overcome the forces of attraction between the naphthalene molecules

2. (a) i. polymer is a large molecule made up of many monomer which are covalently bonded

ii. Polyvinyl chloride pipe does not rust, iron pipe rust

iii

(b) i. Steel barIi reinforced concrete is stronger than concrete

(c) i. because glass is chemically inert/chemically unreactiveii. silicon dioxide, sodium oxide, calcium oxideiii. fused glass/ borosilicate glass

(d) Roof tile/ bricks

3. (a) Zn + CuSO4 ZnSO4 + Cu(b) 100 x 4.2 x 20 = 8400J or 8.4kJ (teacher forget to provide

temperature, initial temperature = 25oC, highest temperature = 45oC, specific heat capacity = 4.2 J g-1 oC-1)

(c) MV/1000 = 0.1 mol(d) 84kJ/mol (please change the magnesium to zinc)

(e)

(f) because small amount of heat energy loss to surrounding //small amount of heat energy absorbed by apparatus such as thermometer and plastic cup.

4. (a) hydrogen gas(b) Zn + 2H+ Zn2+ + H2

(c) size of zinc powder is smaller, this increase the surface area exposed to collision, frequency of collision increase, so that frequency of effective collision increase, rate of reaction is higher.

(d) sulphuric acid is diprotic acid, one mol of sulphuric acid produce two mol of hydrogen ion. When the concentration of hydrogen ion is higher, frequency of collision increase, frequency of effective collision increase, rate of reaction is higher.

(e)

5. (a) zinc ion(b) (i) oxygen gas

(ii) nitrogen dioxide gas

(c) anion is nitrate ion, NO3-.

2cm3 of dilute sulphuric acid and 2 cm3 of Iron (II) sulphate solultion is added into solution of salt K in a test tube, following by a few drops of concentrated sulphuric acid is added down the side of test tube, brown ring formed.

(d) solid Q is yellow when hot and white when cold(e) 2Zn(NO3)2 2ZnO + 4NO2 + O2

(f) i. sodium carbonate//potassium carbonate//ammonium carbonate solution

ii. double decomposition

6. (a) i. Allow movement of ions to complete electric circuitii. from direction of potassium iodide solution to bromine wateriii. colourless to browniv. 2I- I2 + 2ev. bromine watervi. 0 to -1

(b) i. provide/produce oxygen gas to react with metal X, Y and Iron.ii. X : zinc

Y : magnesiumiii. glows brightly and produce a brown powderiv. iron, X, Y

Aqueous solution of salt K

Insoluble carbonate salt

Solution T

7. (a) i. Y + Z2 YZ2

ii. -high melting and boiling point-soluble in water but insoluble in organic solvent-conduct electricity in molten and aqueous state

(b) -group 17 and period 3-electron arrangement is 2.8.7-number of valence electron is 7-3 shells filled with electrons

(c) i. -Electron arrangement for atom X is 2.4 -Atom X (2.4) needs 4 electrons to achieved stable octet electron

arrangement, -So atom X contributes 4 valence electrons to share with 2 Q atoms.

-Electron arrangement for atom Q is 2.6-Atom Q (2.6) needs 2 electrons to achieve stable octet electron arrangement

-So, each atom Q contributes 2 valence electrons to share with X atom.

-Atom X and 2 atoms Q attracted by using covalent bond -A covalent compound with chemical formula XQ2 is formed -draw electron arrangement of XQ2

ii. -Electron arrangement for atom Y is 2.8.2-Atom Y donates 2 valence electrons to achieved stable octet electron arrangement.

-Electron arrangement for atom Z is 2.8.7-Each of atom Z receives one electron to achieved stable octet electron arrangement.

-Ion Y2+ and ions Z- are attracted together by using strong electrostatic force (ionic bond)

-Ionic compound YZ2 formed.-draw electron arrangement of YZ2

8. (a) i. hydrocarbon is a molecule containing carbon and hydrogen element only

ii. -saturated hydrocarbon contain only carbon-carbon single bond//saturated hydrocarbon has maximum number of hydrogen atoms

-unsaturated hydrocarbon contain at least one carbon-carbon double bond//unsaturated hydrocarbon is not bonded to the maximum number of hydrogen atoms

iii. -pour butane into a test tube-add a few drops of bromine water into the test tube and shake-repeat the steps 1 and 2 by using butane-butene decolourised the brown bromine and butane shows no change.OR

-pour butane into a test tube-add a few drops of acidified potassium manganate(VII) solution into the test tube and shake

-repeat the steps 1 and 2 by using butane-butene decolourised the purple acidified potassium manganate(VII) solution and butane shows no change.

iv.

v. reagent : hydrogen gascondition : 180oC, 1 atm, nickel catalyst

(b) i. -bacteria in latex produce lactic acid-hydrogen ions from lactic acid neutralize the negative charged of protein membrane of latex

-rubber particles collide each other and cause protein membrane of latex break up

-rubber polymers combine together to form large lump of rubber polymer which then precipitate out of latex.

ii. - alkali provides hydroxide ion (OH-)-hydroxide ion neutralise hydrogen ion (H+) produced by lactic acid from bacteria.

-Rubber particles remain negatively charged and hence rubber polymer cannot combine and coagulate

9. (a) i. cell P : electrolytic cellCell Q : voltaic cell//chemical cell //simple cell

ii. anode half equation : Cu Cu2+ + 2eobservation : copper electrode dissolves//become thinnercathode half equation : Cu2+ + 2e Cuobservation : brown solid deposited at copper

electrode//become thicker

iii. negative terminal//anodehalf equation : Mg Mg2+ + 2eobservation : magnesium electrode dissolves//become thinner

positive terminal//cathodehalf equation : Cu2+ + 2e Cuobservation : brown solid deposited at copper

electrode//become thicker

iv. diagram for electrolytic cell (cell P) and simple cell (cell Q)

(b) chemicals : iron key, silver plate, 1.0 mol dm-3 silver nitrate solutionProcedure

1. The iron key is polished with sandpaper2. Two-third of a beaker is filled with 1.0 mol dm-3 silver

nitrate solution.3. The silver plate is connected to the positive terminal of

battery as anode4. The iron key is connected to the negative terminal of

battery as cathode5. The switch is turned on, a 0.5A current is adjusted using

rheostat.6. The iron key is rotated slowly after the current is turned on7. The current is turned off after 30 minutes.

Chemical equationAnode : Ag Ag+ + eCathode: Ag+ + e AgObservationAnode : silver plate dissolves//become thinnerCathode: shiny grey solid deposited at iron key

10. (a) part X : hydrophobic part

Part Y: hydrophilic partPart X soluble in grease but insoluble in waterPart Y soluble in water but insoluble in grease.

(b) -Hard water consists of calcium ions and magnesium ions.-In Experiment I, soap ions react with magnesium ions and calcium -ions in hard water to form scum-This reduces the amount of soap ions available for cleansing.-In Experiment II, detergent ions do not form scum in hard water,-Detergent ions form soluble substance with magnesium ions and calcium ions in hard water.

-Detergent is more effective than soap in hard water, detergent is more suitable as a cleansing agent to remove stain in hard water

(c) patient X : analgesicPatient Y : antibioticPatient Z : psychotherapeutic medicines

(d) i take after meal/food// swallowed with plenty of water because the medicine irritates the lining of stomach and cause bleeding

ii -to make sure all the bacteria are killed-Otherwise, the bacteria may immune/resistant to the antibiotic, the antibiotic become not effective-The patient may become ill again-Patient needs stronger antibiotic to fight the same infection

iii Drowsiness and poor coordination

Answer Seminar Chemistry 2011 (Paper 3)

1. (a) test tube 1 : Iron nail rust slow, iron (II) ion is presenttest tube 2 : iron nail rust fast, iron (II) ion is presenttest tube 3 : iron nail does not rust, iron (II) ion is absenttest tube 4 : iron nail does not rust, iron (II) ion is absent

(b) In test tube 2, iron nail rust, iron (II) ion is present, so shows blue colouration in agar solutionIn test tube 3, iron nail does not rust, iron (II) ion is absent, so no blue colouration formed.

(c) When iron nail in contact with more electropositive metal, the metal inhibit the rusting of iron nail. When iron nail in contact with less electropositive metal, the metal speed up the rusting of iron nail.

(d) Manipulated : type of metal in contact with iron nailResponding : intensity of blue colouration//intensity of blue and pink

colouration//rusting of iron nailConstant : Iron nail

(e) rusting occur when iron nail in contact with copper or without contact with any metal in agar solution containing potassium hexacyanoferrate (III) and phenolphthalein, blue colour formed.

(f)Metals that inhibit rusting Metals that speed up rustingMagnesium, zinc copper

(g) copper, iron, zinc, magnesium

(h) to test the presence of iron (II) ion in agar

(i) -using protective coating such as oils, grease and paints.-tin plating-galvanising

(j) i. the longer the time taken, the greater the amount of rust formedii. less than 5 days

2. (a) to compare the heat of combustion of methanol, ethanol and propanol.

(b) manipulated : type of alcohols//methanol, ethanol, propanolResponding : heat of combustion of alcoholsConstant : copper can//volume of water

(c) when the number of carbon atom per molecule increase, the heat of combustion increase

(d) ethanol, propanol, butanol, 200cm3 distilled water, 100cm3 measuring cylinder, copper can, tripod stand, thermometer, electronic balance, windshield, lamp

(e) -200cm3 of distilled water is measured and pour into copper can.-initial temperature of distilled water is recorded.-the copper can is placed on tripod stand -a lamp is filled with methanol and its mass is measured and recorded.-A windshield is placed and the lamp is lighted immediately-Adjust the lamp with a wooden block to make sure the flame from the burning methanol touches the bottom of the copper can.

- The water is stirred throughout the experiment-When the temperature of water increases by 30oC, the flame is put off and the highest temperature reached by the water is recorded

-the mass of the lamp and its contents is weighed immediately and recorded.

-repeat steps 1 to 9 by using ethanol and propanol.

(f)Alcohol methanol ethanol Propanol

Initial temperature of distilled water/oCHighest temperature of distilled water/ oCTemperature rise/ oCMass before burning/gMass after burning/gMass of alcohol burnt/gHeat of combustion/kJ mol-1

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