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CHEMISTRY (Obj and Essay) Neco 2016 Free Expo Answers




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Tuesday 21st June
CHEMISTRY (obj and essay) 10:00am-1:00pm
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CHEMISTRY ANSWERSÂ
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CHEMISTRY OBJ:
1-10: DCBBCBBEDC
11-20: CADECEBBDC
21-30: EEBABDADBE
31-40: AECCACDDDC
41-50: DABABCBBCA
51-60: CBBAABCADE
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VERIFIED ANSWERS
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1ai)
A mixture contains two or more constituents which can easily be seperated by physical methods

1aii)
magnesium trioxonitrate(v) = Mg(NO3)2
molar mass of Mg(NO3)2
=(1*24) + 2 (14*1 + 16*3)
=24 + 2 (14 + 48)
=24 + 28 + 96 = 148g/mol
% of nitrogen = 2*24*100/148
% of nitrogen = 48*100/148
% of nitrogen = 4800/148
% of nitrogen = 32.43%

1aiii)
i)calcium oxide (CaO)
ii)calcium choride (CaCl2)

1bi)
CnH2n+1OH

1bii)
hydrolysation

1biii)
i)displacement reaction
ii)double decomposition reaction
iii)decomposition reaction
iv)catalytic reaction
v)reversible reaction

1biv)
i)endothermic heat change
ii)exothermic heat change

1ci)
i)methyl orange
ii)phenolphthalein
iii)litmus

1cii)
NH4Cl+Ca(OH)2----->CaCl2+2NH3+2H2O

1ciii)
it is collected by upward delivery

1civ)
mass of gas = 1.58*22.4 = 35.392
vapour density = 35.392/1
relative molecular mass= V . D * 2
=35.392*2
relative molecular mass= 70.784
==================================

5ai)
i)carbon monoxide and hydrogen
ii)carbon monoxide,carbon dioxide,hydrogen and nitrogen

5aii)
i)colloids is an intermediate between true solution and a suspension
ii)condensation is the process by which water vapour in the air is changed to liquid water

5bi)
CaC03+2HCl----->CaCl2+H2O+CO2

5bii)
i)it is used in fire extinguishers
ii)it is used in the manufacturing of mineral water
iii)carbon(iv)oxide is used as a coolant in nuclear reactors

5biii)
i)Cr2O7^-2
=2Cr + C-2*7) = -2
2Cr - 14 = -2
2Cr = -2 + 14
2Cr/2 = 12/2
Cr = 6
ii)Cr2{SO4}3
2Cr + 3 (-2*1 + -2*4) = 0
2Cr + 3 (-2 - 8) = 0
2Cr + 3 (-10) = 0
2Cr - 30 = 0
2Cr/2 = 30/2Â
Cr = 15

5ci)
vulcanization is a chemical process of converting netural rubber or related polymers into more durable materials through the addition of sulphur or other equivalent curatives or accelerators

5cii)
Time Taken(t) for 6.35g of copper(ii)tetraoxosulphate
solution
Cu^2^+ + 2c ------->Cu
Q = 2*63.5*95600
Q = 12255500
Q = 1t
12255500/10 = 10*t/10
t = 1225550/60 = 204258.3

5ciii)
Latex
==================================

4ai)
electrolytic cell is a cell that consist of a container of electrolyte with two electrodes connected to a suitable direct current supply

4aii)
i)daniel cell
ii)Leclanché cell

4aiii)
i)copper
ii)tin

4aiv)
action of dilute acide on zinc

4av)
Zn+2HCl------>ZnCl+H2

4bi)
i)dinitrogen(i)oxide(N2O)
ii)nitrogen(v)oxide(N2O5)
iii)nitrogen(iv)oxide(NO2)

4bii)
charle's law states that the volume of a fixed mass of gas varies directly with the absolute(kelvin)temperature provided the pressure remains constant.

4biii)
P1 V1 = P2 V2
given that
P1 = 900mmHg
P2 = 750mmHg
V1 = 300cm^3
V2 = ?
V2 = P1V1/P2
V2 = 900*300/750
V2 = 270000/750
V2 = 360cm^3

4biv)
% composition carbonÂ
= 12/(12*6) + (1*6) *100%
= 12/72+6 *100
= 12/78 * 100% = 1200/78%
%composition of carbon = 15.38%

4c)
TABULATE
-THERMOPLASTS-
i)it melts when heat is applied to it
ii)highly recycled
-THERMOSETS-
i)does not melt when heat is applied
ii)cannot be recycled
==================================

2ai)
ionization energy deals with electron loss while electron loss while electron afinity deals with electron gain

2aii)
i)they are used to dry gases
ii)they are used to recover valuable vapours from industrial effluents and refine petroleum

2bi)
TABULATE
-RHOMBIC SULPHUR-
i)bright yellow in colour
ii)it is octohedral in shape
-MONOCLINIC SULPHUR-
i)amber in colour
ii)it is needle like in shape

2bii)
oxygen = 60%
sodium = 40%
oxygen 60/16
3.75/1.74 = 2
sodium 40/23
1.74/1.74 = 1
the emperical formula is NaO2

2biii)
sodium(iv)oxide

2ci)
i)x is hydrophobic region
ii)y is hydrophilic religion

2cii)
i)for laundry purpose
ii)for fuel

2ciii)
i)the distance of outermost electron from the nucleus
ii)the size of the positive nuclear charge
iii)the screening effect of inner electrons

2civ)
period law states that the properties of the elements are a period function of their atomic number

2di)
n---pentane----->n---butane----->2---methylbutane---2,2---dimethylpropane

2dii)
i)glucose
ii)galactose

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Completed. enjoy.
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