NABTEB GCE chemistry Questions and Answers  2019 Nabteb GCE

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NABTEB GCE Nov/Dec chemistry ANSWER

Chemistry Paper I Thursday 28/11/19 9.00a.m -12.20p.m

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*NABTEB GCE CHEMISTRY SOLUTIONS*

*CHEMISTRY OBJ*
1-10: CBBCBCDBCC
11-20: CBADADACCD
21-30: DBDCBCADDA
31-40: CACDCCCBAC
41-50: CCDDBABBDA

(1ai)
Mixture contains two or more substances which are not chemically combined together and they can be separated by physical means eg salty water, Alloys etc.

(1aii)
Fractional Distillation

(1b)
(i) Physical change.
(ii) Chemical change.
(iii) Physical change.

(1ci)
Electrode is a metal plate where the conventional current pass in and out in it.
They are positive electrode(+ve) or negative electrodes.
They are inform of wires or rods.

(1cii)
During electrolysis, ions move towards the electrodes. When ion reaches the electrode, they either lose or gain an electron depending on their charge. Negative charged ion lose electrons to become neutral atoms via gaining electrons. Gaining is called reduction. Anions in the electrolysis are then attracted to the positively charged anode, where they give up their electrons to become electrically neutral; and the cation accept electrons to become electrically neutral and discharged.

(1ciii)
(i) They are partially filled d-orbitals.
(ii) They form complex ions.
(iii) They are coloured metals.
(iv) They show variable oxidation states.

(1di)
Cassiterite

(1dii )
SnO2+2C(s)–>Sn(l)+ 2CO(g)

========================================================

(2ai)
X = 90% 39X
19

10% 41X
19

41X
19
No of ē = 19ē

(2aii)
No of neutrons in 39X
19
= 39 – 19
= 20

(2aiii)
No of neutrons in 41X
19
= 41 – 19
= 22

(2b)
(i) Distillation: This is the purification of a liquid by heating it to its boiling point causing vaporization and then condensing the vapour into the liquid state and collecting the liquid.

(ii) Filtration: This is the separation of mixture base on different sizes. The ones with small sizes will pass through the filter or porous layer which is called filtrate while the residue will be left in the filter.

(2ci)
2H2S(g) + SO2(g) –> 3S(g) + 2H2O(l)
The entropy in the reaction above is positive (+ve)

(2cii)
NaCl(s)–>Na+(aq) + Cl-(aq)
The entropy in the reaction here is positive(+ve)

(2d)
CH₃(CH₂)₂CH₃ > (CH₃)₃CH

======================================================

(3ai)
(i) Copper
(ii) Silver

(3aii)
Calcium Floride is added to lower the melting point from 850°c to about 650°c

(3b)
(i) It is because it is cheap, light and good conductor.
(ii) It is light and has good electrical conductivity.
(iii) It is due to its high reflectivity.

(3c)
(i) It is used for extraction of metals.
(ii) It is used for purification of metal.
(iii) It is used for electroplating of one metal by another.

Solution:
MNa = 7.1g
Q = ?
MNA = 23g/mol
n = M/M
n = 7.1/23 = 0.3087
n = 0.31moles

Q = nF
Q = 0.31×96500 =
Q = 29,915C
NaCl <===> Na+ + Cl-

===================================================

(4ai)
With chlorine
C₂H₄ + Cl₂ —> C₂H₄Cl₂(1, 2dichloro ethane)

With Hydrogen(Hydrogenation)
C₂H₄(g) + H₂(g) –>C₂H6(g)

(4aii)
Draw the hydrocarbon [https://i.imgur.com/4v8wSDT.jpg]

C6H6+Cl₂–>C6H5Cl+ Hcl

(4aiii)
Esterification of ethanol

C₂H5OH + CH₃COOH –> CH₃COOC₂H5 + H₂O

(4bi)
CH₃(CH₂)₂OH
H H H
| |
H – C – C – C – OH
| |
H H H
Propan – 1 – 01

(4bii)
-OH (Hydroxyl group)

(4ci)
Let’s Chatelier’s principle states that if a chemical system is in equilibrium and one of the factors involved in the equilibrium is altered, the equilibrium will shift so as to neutralize the effect of the change.

(4cii)
Kc = [NH₃]²/[N₂][H₂]³

(4ciii)
Endothermic reaction

(4civ)
Draw the diagram [https://i.imgur.com/9yGXOgB.jpg]

======================================================

(5ai)
Electrolyte conduct electricity and are salts or molecules that ionize completely in solution, eg H₂SO₄ while non electrolyte does not conduct electricity and does not dissociate into ions in solution. Eg Sugar cane

(5aii)
(i) Electrolyte is a substance which conducts electricity in only molten form while conductor has the ability to conduct electric current either in molten or in solid state.

(ii) Electrolytes are ionic compounds which dissolved in water and get dissociated into +ve and -ve ions while conductors are substances that can pass on heat or electricity from one medium to another.

(5bi)
Faraday’s first law of electolysis states that the mass(m) of a substances liberated at an electrode during electrolysis is directly proportional to the quantity of electricity (Q) passing through the electrolyte.
M α Q
M = EQ
E = M/Q
Where m = mass
Q = change
E = electrochemical equivalent.

(5bii)
Draw and describe the experiment [https://i.imgur.com/1MLqnat.jpg]

(5biii)
M = 0.222g
M²+ +2e- —>M
N.E = 2
I = 0.45A
t = 25×60 = 1500s
M = ?
I t/N.E×F = m/M
0.45×1500/2×96500
= 0.222/M
M = 2×96500×0.222/0.45×1500
= 42,846/675
M = 63.5
Cu = 63.5g

(5ci)
Cathode = spoon
Anode = Pure silver

(5cii)
Potassium argentocyanide.

(5ciii)
(i) Purification of metals.
(ii) Extraction of metals.
(iii) Industrial preparation of certain chemicals.

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