8/9/2019 Upp2.f4.2010.Chemistry.answer

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Section A : Objective

1 B 7 A 13 B 19 A 25 D

2 D 8 B 14 D 20 B 26 C

3 A 9 D 15 D 21 A 27 C

4 B 10 D 16 B 22 D 28 C

5 D 11 A 17 D 23 C 29 A

6 D 12 A 18 A 24 B 30 D

Section B : Structure

1

a) i) (21.45 g 19.25 g) = 2.20 gii) (21.45 g 20.32 g) = 1.13 g

b) Relative formula mass of MgSO4 = 24+32+(16x4) = 120

c) Mass of dehydrated magnesium sulphate salt = (20.32 g 19.25 g) = 1.07 g

Number of moles of dehydrated salt = (1.07/120) = 0.009 mole

Number of moles of water of crystallisation = (1.13/18) = 0.063 mole

d) 0.009 mole of dehydrated magnesium sulphate salt combines with 0.063 mole of water of crystallisation

Therefore, 1 mole of dehydrated magnesium will combine with (0.063/0.009) = 7 moles of water of

crystallisation.

e) MgSO4.xH2O = MgSO4.7H2OThe value of x is 7.

f) i) Formula : MgSO4.7H2Oii) Equation : MgSO4.7H2OMgSO4 + 7H2O (Heating)

g) Copper sulphate pentahydrate

2

a) C, D, I, E

b) i) D2+

ii) G-

c) I

d) A. It has achieved duplet electron arrangement

e) E

f) i) G

ii) The atomic radius of G is shorter than H. Atom G has greater tendency to accept electron.

g) i) C

ii) 2C + 2H2O 2COH + H2

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a) i) P2Q

ii) Ioniciii) Relative formula mass of P2Q = 2(23) + 16 = 62

iv) The compound dissolves in water to form an alkaline solution

b) i) XY4

ii) Covalent

iii) Relative formula mass of XY4 = 12+4(35) = 152iv) The compound has low melting and boiling points

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a) Period 3, Group 16

b) i) Atomic radius decreases across the period

ii) Increasing number of protons exerts stronger electrostatic attraction on the electrons and pulls themcloser to the nucleus

c) Electronegativity increases

d) i) Aluminium

ii) Aluminium oxide reacts with both acids and alkalis

e) Sodium and magnesium

f) i) Sodium

ii) 2Na + H2O 2NaOH + H2

g) i) Chlorine

ii) Cl2 + 2NaOH NaCl + NaClO + H2O

h) i) Silicon

ii) Use as semiconductors for transistors in electronic equipment

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Section C : Essay

1

a) i) To improve the appearance of the spoon because silver metal gives a shiny surface to the spoon

ii) To prevent corrosion of iron

b) Labeled diagram

c) At anode,- The silver anode ionises

- Each silver atom loses one electron and forms silver ion

- Ag(g) Ag+(aq) + e

-

- The electrons flow from the anode to the cathode along the wires

At cathode,

- The silver ion discharged- Each silver ion accepts one electron and forms silver atom which deposits on the iron spoon

- Ag+(aq) + e

- Ag(s)

d) - Aluminium is extracted from bauxite (Aluminium oxide)

- Aluminium oxide is heated until it melts- Cryolite is added to lower the melting point of aluminium oxide- The molten aluminium oxide is electrolysed using carbon electrodes

- Al2O3(s) 2Al3+

(l) + 3O2-

(l)

- The aluminium ions move to the cathode and discharge by accepting electrons- Al3+(l) + 3e- Al(l)

- The oxide ions move to the anode and discharge by releasing electrons

- 2O2-

O2(g) + 4e-

- The oxygen gas produced reacts with the carbon anode to produce carbon dioxide gas

- Thus, the anode must be replaced from time to time

Anode : Silver electrode

Cathode : Iron spoon

Electrolyte : 0.2 mol dm-3

silver nitrate solution

Includes :

- ammeter

- rheostat