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Waec 2016 Chemistry objective and essay Answers and Questions – expo

Waec 2016 Chemistry objective and essay Answers and Questions – expo

VERIFIED WAEC 2016 CHEMISTRY QUESTIONS AND ANSWERS

Monday 18th April 2016
CHEMISTRY 2 (ESSAY) 2.00PM – 4.00PM
CHEMISTRY 1 (OBJ) 4.00PM – 5.00PM

CHEM OBJ
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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^6,3s^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) Al2 O3(Aluminum oxide)
ii) sodium hydride (NaH)
iii)zinc trioxocarbonate(iv)ZnCo3
iv)silicon tetrachloride (SiCl4)

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, 3d^10, 4s^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)
Na2Co3 + MgCl2 —->2NaCl + MgCo3
1mole 1mole 2mole 1mole
molar mass of Na2 Co3 = 2 * 23 + 12 * 1 + 16 * 3 = 46+12+48 = 106g

==================================

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

==================================

5ai)
Na2S2O3 ===>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)
I2KNo3. ——–>2KNO3 + O2
2AgNo3 ———>. 2Ag + 2No

5ci)
Calcium chloride in a solution can give rise to crystal using filteration and evaporation to dryness. The sol is filtered into filtrate and residue b4 evaporation to dryness takes place.

5cii)
– Because of presence of hydrogen bonding in NH3
– Because Iodine as higher molecular mass than chlorine

Posted by on April 17, 2016.

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