KCSE Past Papers 2013 Chemistry paper 1 (233/1)

1.a)X is water. or H20

b)It is slightly soluble in water. J and denser than air.

c)

2AgNO3(s) – > 2Ag(s) + 2NO2(g)+O2(g)

21= 04m -> F6203“) + SO + (1)

3.

b) Sulphur has a tinged structure of S8 molecules whiles chlorine is diatomic.

The forces in sulphur are stronger than chlorine.

5. a) It does not sublime.

b) Cut a piece of Sodium metal, place it on a defiagrating spoon, heat it briefly

then lower it into a gas jar of chlorine . It will continue buming forming Sodium Chloride.

6 a) Cu2+(aq) + 2e —> Cu(s)

b) 63.5 g require 2 x 96500 C

l.l84g = 63.5

3598.6 coulombs J (1)

Q = 1.7.92.2.

3586.5 = 2xt 60

35865 =t = 29.988

2

z 30 minutes )

1799.3 s =t (V2)

7 (a) (i) X – Calcium carbide or CaC,

(ii) Y – CH2 = CHCl Chloroethene or vinylchloride

(b)

less than B because of its heavier mass.

9. ln water. HCI is ionised ginto H and Cl the Chloride ions are oxidised to chlorine gas by potassium permanganete.

In methylbenzene, HCl remains in molecular gform i.e HCl. The Chloride is not available for oxidation hence no reaction. 10 (a) T (b) l5 g t/111 (c) Fractional crystallization

11 (a) NZHW + Ow ~> NMI + 2H:O

(b) Bond breaking energy

l63 + 4 (388) + 496

= 2211 kJ

Bond making energy

944 + 4 (463)

=_27% kl

Ethalpy change = Bond breaking + Bond making energies.

2211 +(-2796)

= -585 kl/mol

12 a) The acidified permanganete will be decolourised (purple to colourless) b) The permanganate (Vll) is reduced to manganese (II) ion.

(i) A white precipitate forms.

(ii) Ba2+ +SO2-/3 —> BaSO_

13 a) [Zn(NH4/3]2+

b) Zn2= + Mg —> Mg2+ + Zn

14 .Charles Law

At constant pressure. the volume of a fixed mass of gas is directly proportional to its absolute temperature. 1

b) 1 = vs km

P 1v [Ht = I46 dp

_1_r =T l1=l8+._73:36lK

T : P3: 10! km

P1 v =12?

T 1><36l H TI:-

98.39 l-16

T 4849313

14364.94 ~ 1-

r = 273.22 K

15. a) R and T

b) T

16 Zinc granules

The gradient of the graph is less” steep (11 because there is less surface area.

17 NO + O —> 2NO

b) Because nitrogen is inert.

c) Nitrogen (ll) oxide is oxidised to Nitrogen (IV) oxide which is a pollutant. H

18 (a) Water

(b) Bubbles of gas and a white ppt CO2. (P/Q) reacts to give CaCO,

19 (a) These are different forms carbon in the same physical state.

(b) The hexagonal graphite rings have weak Van der Waals forces between the layers that allow the layers to slide over each other (1) while in diamond the atoms are held by strong Covalent bonds. .

20 (a) The atomic radii increase with increase in atomic number. This is due to increase in energy levels.

(b) The group II elements have more protons than group I elements hence this increases the nuclear attraction for the outer electrons. J

21 (a) Cu2 or copper ions

(b) C1 and OH’

22 (a) Copper pyrites chalcocite, malachite

(b) To concentrate the ore

(c) – Brass

– Batteries

23 (a) 100-25=75 cm

(b) CxHy + O2 —> C02 + H20

15 cm’ 75 cml 45 cm

1 5 3

Cx Hy =-Iy + 5 O2—> 3 CO2 + 4 H20

x = 3 y = 8

C3H8 t/(1)

24 Ca(NO3)2 —> Ca + 2NO3

RMM of Ca(NO)2 = 164

Concentration of Ca(NO3)2 = 4.1

Conc. in g/l

RMM

Molarity =

= Q

164

= 0.025M J M)

1 mole Ca(NO3)2 E 2 moles Nitrate

0.025 iii E 2 0.025

0.05M

25 It would remain unchanged (1)

There is no water to form hypochlorous acid

26 When aqueous sodium chloride is added to Ca2 . There is no ppt while a white ppt is formed when aqueous sodium chloride is added to a solution containing Pb

27 (a) N. being a weak acid provides few H’ to be neutralised by OH” hence there is a slight increase in temperature.

(b) CH3COOH + KOH ) —> Cl-l3COOKmq] + H20“)

28 (a) Experiments 1 and 3. J

(b) In experiment 1, the ions in K2CO3 are tightly held in position and cannoot move V

while sugar solution does not have ions that can carry a current in solution.

29 1 H mass 18

2

1 H mass 20