2016 waec chemistry answer here

Waec 2016 chemistry Obj

1-10 CAACDBCABC

11-20 BDBABBBDCA

21-30 BCCABBCACB

31-40 AACDCCCBBA

41-50 ABCBBABBBB




2016 WAEC CHEMISTRY ANSWERS

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

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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%
3D


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



(8ai)Each
successive member of a
homologous series differ by
~CH2~group.Members of a
homologous series show
similar chemical
properties. (8biii)C2H5OH
+CH3CH2COOH=CH3CH2COOC2H5
ethylpropanoate (8biii)C2H5OH
+CH3CH2COOH=CH3CH2COOC2H5
ethylpropanoate (8ai)Each
successive member of a
homologous series differ by
~CH2~group.Members of a
homologous series show
similar chemical
properties. (8biii)C2H5OH
+CH3CH2COOH=CH3CH2COOC2H5
ethylpropanoate.





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