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

Verified WAEC Chemistry Essay/Theory and OBJ Questions and Answer Solution – May/June 2017 Expo Runs Real and correct
 Verified 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<DH3<DH1
========================
2a)
i)periodic law states that properties of elements are the periodic function of their atomic number
ii)periodic property of element is the variation of the properties of element in a regular pattern both down the group and acrose the period
2aii)
i)ionization energy
ii)electron affinity
iii)electropositivity
2aiii)
ionization energy increase from left to right acrose a period because the nuclear charge increase progressively while the screening effect remain constant
-atomic reduis decreases from left to right acrose the period because nuclear charge effect out weighs screening effect,which remains constant because the number of shell in a period is constant
-electron affinity increase from left to right across a period because an additional electron will experience a greater repulsion than altraction from the positively charged nucleus
2b)
the relative atomic mass of an element is the mass of one atom of the element compared with the mass of an atom of the carbon -12 isotope whos mass is exactly 12
2bci)
isotopy
2cii)
the isotopes have difference number of neutron
2ciii)
R.A.M=(75/100*35)+(25/100*37)
=2634.25
2di)
I CO2 by downward delivery
II HCL by downward delivery
III H2 by upward delivery
2dii)
I because it is denser than air
II because it is denser than air
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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
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.
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