WAEC 2017/2018 Chemistry OBJ & Essay Answers – May/June Expo

WASSCE 2017 Chemistry (OBJ/THEORY/ESSAY) Answers Now Available Here

Tuesday, 18th April, 2017
Chemistry 2 (Essay) 2.00pm. – 4.00pm
Chemistry 1 (Objective) 4.00pm – 5.00pm

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CHEMISTRY OBJ
1d 2c 3d 4b 5c 6b 7d 8b 9c 10a
11d 12a 13a 14c 15d 16c 17d 18b 19c 20b
21d 22b 23c 24b 25c 26c 27d 28b 29a 30b
31b 32a 33c 34b 35a 36c 37c 38c 39c 40d
41b 42d 43a 44c 45a 46b 47d 48a 49b 50d
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5ai)
worm the unknown substance with concentrated H2SO4 in a test tube. if trioxonitrate(v) ion’s are/is present, some trioxonitrate(v) acid will be condensed as oily drops on the upper part of the tube. On further heating, the acid decomposes yielding brown fums of NO2 gas.

5iia)
Sodium chloride is used for:
i)preserving food
ii)glazing pottery

5iib)
Sodium trioxocarbonate(iv) is used for:
i)standardizing acids in the laboratory
ii)the manufacture of glass

5bi)
C(s) + O2(g) =====> Co2(g)
Co2(g) + C(s) =====> 2Co(g)
Fe2O3(s) + 3Co(g) =====> 2Fe(l) + 3Co2(g)
The limestone present decomposes as follows:
CaCo3(s) =====> CaO(s) + Co2(g)
Which is available to remove silicon(iv) oxide impurity
SiO2(s) + CaO(s) =====> CaSiO3(s)

5bii)
Faraday’s first law of electrolysis states that, the mass (m) of an element discharged during an electrolysis is directly proportional to the quantity of electricity (Q) passing through it.
===============

1ai)
an acid base indicator is a weak acid or weak base that exhibits a colour change as the concentration of hydrogen (H^+) or hydroxide (H^-) ions changes in an aqueous solution

1aii)
methyl-orange

1b)
i)oxidizing agent
ii)mixed anhydride

1c)
enthalpy of combustion is the heat evolved when one mole of a substance is completely burns in oxygen gas under standard conditions

1cii)
enthapy of combustion is always negetive since it involvs a rise in temperature and heat of reactants is greater than the heat of products

1d)
primary cell is a cell that cannot be re charged while secondary cell is a cell that can be recharged

1dii)
primary cell — daniell cell
secondary cell — lead accumulator

1e)
mole is the unit of measurement in the International System of Units (SI) for amount of substance. The unit is defined as the amount of a chemical substance which contains as many representative particles, e.g., atoms, molecules, ions, electrons, or photons, as there are atoms in 12 grams of carbon-12 (12C), the isotope of carbon with relative atomic mass

1f)
n= V=40cm^3
c= 0.40moldm^3
n=cv/1000
0.40*40/1000 = 0.016mol

1g)
i)carbon or graphite
ii)platinum

1h)
i)induced dipole-induced dipole
interaction or dispersion force
ii)dipole-dipole interaction

1i)
i)carbon(ii)oxide and water or CO and H20

1j)
2bFe^3+-15^2, 2s^2, 2p^6, 3s^2, 3p^6, 3d^3, 4s^2
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3ai)
Thermal cracking

3aii)
C4H8

3aiii)
(I) H H. H
| | |
H-C-C-C=C
| | | |
H H H H
and
(II) H H
| |
H-C-C=C-C-H
| | | |
H H H H

3aiv)
I-normal butene
II -But-2-ene
Ni

3av)
C4H8 +H2 ——-> C4H10
250c

3b)
in other words the oil is stained red. This is a aspecifit test for fats
if suden (iii) is added to fats a distinct red colouration is observed

3c)
Given 2502+02+2H20—>2H2SO4
1mole produce 2mole
1.3mole produce 3mole
moles of H2SO4=3mole
molar mass of H2SO4=(1+2)+32+(4*16)
=2+32+64
=98gmol-^1
mole=mass/molar mass
mass and H2SO4=Mole*molar mass
=3*98
=294g

3di)
DH2

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