2017/2018 NECO GCE EXPO: CHEMISTRY THEORY AND OBJ QUESTIONS AND ANSWERS NOW AVAILABLE HERE

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Exam Time: Thursday 9th Nov. 2017
Chemistry Paper III & II (Objective & Essay)
2.00 pm – 5.00 pm

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NECO GCE CHEMISTRY OBJ AND THEORY ANSWERS FROM EXAMHOT.COM
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CHEMISTRY OBJ:
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1-10: ADEBBDCAAC
11-20: ABBEBDDBCD
21-30: BABDCECEEC
31-40: CBDEBBBCBB
41-50: AECBBEDBDE
51-60: ACEBDCCEDB
Examhot.com #cares

 

 

CHEMISTRY THEORY:
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(1a)
In a tabular form
C; H; O
Mass/molar mass of C is 6.12g/12
Mass/molar mass of H is 0.85g/1
Mass/molar mass of O is 2.72/16

Under C: 0.51
Under H: 0.85
Under O: 0.17

C = 0.51/0.17
H = 0.85/0.17
O = 0.17/0.17

Empirical Formula is C3H5O
Molecular Formula is. ?
Molar mass is 134
[C3H5O]n = 134
[12 × 3 + 1×5 + 16 × 1]n = 134
[36 + 5 + 16]n = 134
57n = 134
n = 134/57
n = 2.35
n = 2
Molecular Formula [C3H5O]2
= C6H10O2

(1bi)
Isotopy – Atom of the same element are alike in every aspect and differ from atoms of all other element
35
17Cl and

37
18Cl

(1bii)
Sub atomic particle: All elements are made up of small indivisible particles called atoms

(1ci)
Diagram

(1cii)
I. 2C2H2 + 5O2 —> 4CO2 + 2H2O
II. C2H2 + HCl —> C2H3Cl

(1d)
Because they are in different states. Steam is in a gaseous state while water is in a liquid state.

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(2a)
(i) Temporary hardness – Dissolved calcium hydrogencarbonate
(ii) Permanent hardness -Dissolved calcium sulfate.

(2bi)
(i) Temporary Hardness can be Removed By Boiling
(ii) Permanent hardness can be removed by use of washing soda (sodium carbonate); ion exchange; the use of polyphosphate water softeners.

(2bii)
-Advantages:
(i) Calcium ions in the water are good for children’s teeth and bones.
(ii) The soothe it forms is good for ceramics purposes.

-Disadvantages:
(i) It is more difficult to form a lather with soap.
(ii) Scum may form in a reaction with soap, wasting the soap.

(2ci)
A saturated solution is a chemical solution containing the maximum concentration of a solute dissolved in the solvent.

(2cii)

(2ciii)
(i) Anthracite Coal
(ii) Bituminous coal
(iii) Subbituminous coal

(2civ)
Coal tar

(2di)
(i) Zinc is not a transition metal because it forms only Zn2+ ions with all the 3d electrons present.
(ii) Zn not a transition metal, because it forms only Sc3+ ions with n d-electrons

(2dii)
Fine chemicalChemical substances prepared to a very high degree of purity for use in research and industry.

(2diii)
(i) dyes
(ii) perfumes

 

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(3ai)
Petroleum Gas and Petrol>Kerosene>Diesel>Asphalt

(3aii)
I. Asphalt
II. Kerosene
III. Petroleum Gas and petrol
Iv. Asphalt

(3bi)
I. Ethene
II. Propene

(3bii)
(i) Structural Isomerism
(ii) Stereo Isomerism

(3biii)
19R – 1s² 2s² 2p6 3s² 3p6 4s¹
10S – 1s² 2s² 2p6
24T – 1s² 2s² 2p6 3s² 3p6 4s² 3d4

(3biv)
Group 6

(3ci)
I. AgNO3 and BaCl2
II. Bacl2 and Na2SO4
III. Ca(NO3)2 and H2CO3

(3cii)
(i) Filtration
(ii) Flocculation
(iii) Disinfection

(3d)
Mass of NaCl
= mass of Nacl + mass of H2O
= (23 + 35.5) + 80g
= 58.5 + 80g = 138.5g
Hence
Since 39.8g at 100°C = 35.9g at 15°C
138.5g at 100°C = Xg at 15°C
X = 138.5 × 35.9/39.8g
= 124.9g at 15°C
Hence mass of Nacl precipitated
= 138.5 – 124.9g
= 13.6g of Nacl

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(4a)
(i) Coke
(ii) Graphite
(iii) Diamond
(iv) Coal
(v) Charcoal

(4b)
Le chatelier’s principle states that for a reversible reaction in equilibrium, if any of the factors(temperature, concentration, pressure) keeping the system in equilibrium is altered, the system will shift to adjust the change

(4bii)
I – It will shift from left to right
II – It will shift from left to right
III – It will favor the forward reaction by increasing the product

(4biii)
Kc = [NH]2
——
[N2][H2]3

(4di)
I. Calcium Hydroxide Ca(OH)2
II. H2SO4
III. H2SO4

(4dii)
I. NaCl
II. NaHSO4
III. K3Fe(CN)6

 

 

 

 

 

 

 

 

 

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