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Waec 2016 Chemistry Answers – May/June Expo

Poster: alexical | Date: 5:24pm, 17th Apr 2016. | Views: 791 | 1 Replies
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alexical . Jalingo, Taraba
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2016 WAEC CHEMISTRY ANSWERS
CERTIFIED CHEMISTRY OBJECTIVES
1-10 caacabcdbc
11-20 babaadbdca
21-30 bccaabcdcb
31-40 abcbcccbbc
41-50abdbbbaabb
1a )
nucleons is the collective name for two
important
sub-atomic particles : neutrons and
protons
1b)
Graham 's law of diffusion states that at
a
constant temperature and presure , the
rate of
diffusion of a gas is inversely proportional
to the
square root of it density
1c )
because when aluminum is exposed to
moist
air, a thin continuous coating of aluminum
oxide
is formed , which prevents futher attack of
the
aluminium by atmospheric oxygen and
water or
steam under normal conditions
1d)
i ) electron - affinity
ii ) electron - negativity
iii ) ionization - energy
1e )
i ) the molecule of real gases occupies
space and
there are forces of the attraction between
them
ii ) real gases do liquefy when their
temperature
droops .
1f )
i ) used in seperation of different
component of
crude oil .
ii )it is used for separating acetonic from
water
iii ) it is used for obtaining different gases
from air
for industrial use .
1g)
i ) concentration of ions in electrolyte
ii )the nature of the electrode
iii )the position of ions in the
electrochemical
series
1h)
i ) substitution reaction
ii )addition reaction
1i )
i ) carbon dioxide
ii )water vapour
iii ) carbon monoxide
1j )
i ) centrifugation
ii )sieving
iii )evaporation to dryness
==================================
2a )
i ) isotopy
ii ) they have the same number of proton
(atomic
number) but different mass number
iii ) oxygen ,carbon
iv )1s ^2, 2s ^2, 2p^6 ,3 s ^2, 3p^5
2bi)
PHYSICAL PROPERTIES
METAL
i ) high melting and boiling point
ii ) they are good conductor of heat and
electricity
NON -MATEL
i ) they have lower melting and boiling
point
ii )they are poor conductors of heat and
electricity .
CHEMICAL PROPERTIES
METAL
i ) they form basic and ampheric oxides
ii )the react by electron lose or donation
of
electron
NON -METAL
i ) the form acidic oxides
ii )the react by sharing and accepting
electrons
2bii )
i ) Al 2 O 3(Aluminum oxide )
ii ) sodium hydride (NaH )
iii )zinc trioxocarbonate( iv )ZnCo 3
iv )silicon tetrachloride (SiCl 4)
2ci )
i ) variable oxidation states
ii ) complex ion formation
iii ) they possess strong metallic bonding
2cii )
1s ^2, 2s ^2, 2p^6 , 3s ^2, 3p^6, 3 d^10, 4
s ^2
2ciii )
Zinc is not considered as a typical
transition
element bacause it has only one oxidation
state
of +2 , it metallic ion are not coloured and
it is not
used as a catalyst.
2d)
Na 2Co 3 + MgCl 2 -- -- > 2NaCl + MgCo
3
1mole 1mole 2 mole 1mole
molar mass of Na 2 Co 3 = 2 * 23 + 12 * 1
+ 16 *
3 = 46+ 12+48 = 106g
==================================
5ai )
Na 2S 2O 3 ===> 2 + 2x + 6 = 0
2x = 6 - 2 = 4
X = 4/2
X = 2
The oxidation number of sulphur is 2
5aii )
Rhombic & monoclinic
5aiii )
- Both are tetravalent
- both are allotrope of carbon
5bi)
CO2 & Chloroflorocarbon
5bii )
There is increase in sun radiation reaching
the
earths surface ie Global warming
5biii )
ThunderStorm
5iv )
I 2KNo 3. - -- - -- -- > 2KNO3 + O 2
2AgNo 3 -- -- - -- -- > . 2Ag + 2No
5ci )
Calcium chloride in a solution can give rise
to
crystal using filteration & evaporation to
dryness .
The sol is filtered into filtrate & residue b4
evaporation to dryness takes place .
5cii )
- Because of presence of hydrogen
bonding in
NH 3
- Because Iodine as higher molecular
mass than
chlorine
5di)
Mol of Nacl = Mass / MM
= 5 . 85/ 58. 01
= 0 . 1mol
From the equation
2mol of Nacl gives 2mol of HCL, 0. 1mol
of Nacl
gives 0. 1mol of Hcl
Vol of Hcl = 0. 1 x 22. 4 = 2. 24mol /dm^3
No 3
(I) % of carbon = 100 - 14.3 =85.7%
=> C/12.0 , 4/1.0
=> 85.7/12.0 , 14.3/1.0
7.142. , 14.3
Decide both sides by the smallest
7.142/7.142. , 14.3/7.142
1. , 2
=> E. F =CH2
II) (CH2)n = molar mass
But n =volume /molar mass
2.24/22.4 = 0.1mol
Molar mass = mass/amount = 7.0/0.1 =
70g/mol^-1
CHEMISTRY
3ai)
structral isomerism is the existance of two
or more compounds ( known as isomers)
with the same molecular formula but
different molecular structures
3ai)
i) tertiary alkanol
ii) secondary alkanol
iii) primary alkanol
3bi)
i) 2[CH3 CH2 COOH ] 2K(s)---->
ii) [CH3 CH2 COO ] K + H2
i) 2[CH3 CH2 COOH ] +2 K(s) ------>
2[ CH3 CH2 COO ] K + H2
ii) CH3 CH2 COOH + C4 H9OH
HEAT---->CH3 CH2 COO C4 H9 + H20
H2SO4
iii)CH3 CH2 CH2 CH20H + H^+
KMnO4------> CH3 CH2 CH2 CH2 - 0H
EXCESS
3bii)
i) potassium ethanoate,hydrogen
ii) butyl propanoate and water
iii) enthanal
3c)
the percentage composition of the
hydrocarbon
= 100
H + C = 100
14.3 + C =100
C= 100 - 14.3
C= 85.7%
================
(4ai)
calcium chloride, CaCl2
(4aii)
to the unknown ssubstance in a gas jar,
add small quantity of lime water. if the
gas is carbon(iv)oxide, it turns lime water
milky while carbon (ii) oxide has no effect
(4bi)
oxygen is releasedf abundantly from air
and nitrogen is produced by the reaction
of potassium trioxonitrate(v) with
concentrated hydrochloric acid
(4bii)
oxygen gas rekindle a lighted splint while
nitrogen does not
(4ci)
Bauxite is preferred because it is readily
available in the earth crust
(4cii)
-trioxosilicate(iii)
-carbon(iv)oxide
(4ciii)
-it helps to purify the bauxite
(4civ)
it is difficult to extract aluminium by
chemical reduction of aluminium oxide in
amphoteric
(4cv)
AL2O3+NaOH=>Na2O + Al+ H20
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