WAEC Chemistry OBJ And Theory/Essay Expo Answer – 2017 May/June

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100% Correct WAEC Chemistry Essay/Theory and OBJ Questions and Answer Solution – May/June 2017 Expo Runs

Verified WAEC Chemistry
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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
==============
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 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.

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