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WAEC 2016 CHEMISTRY OBJ AND THEORY ANSWER




Waec chemistry 2016 OBJ and theory answer


1a)Nucleons is made up of neutrons & proton in an atom OR nucleons is the collective name for two important sub-atomic particles:neutrons and protons in an atom.

1b)
Graham's Law of diffusion state that, the rate of difussion of a gas is inversely proportional to the square root of its vapour density. Provided that Temperature remains constant.
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1c)
Aluminium react with oxygen to form a thin impervious layer of oxide.
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1d)
- atomic radius
- electro-negativity
- ionization energy
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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.
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1g)
- concentration of ions in electrolyte
- the nature of the electrode
- the position of ions in the electrochemical series

1h)
- substitution reaction
- addition reaction
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1i)
- carbon dioxide
- water vapour
- carbon monoxide
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1j)
- centrifugation
- sieving
- evaporation to dryness
==================================
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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
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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.
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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
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2bii)
i) Al2 O3(Aluminum oxide)
ii) sodium hydride (NaH)
iii)zinc trioxocarbonate(iv)ZnCo3
iv)silicon tetrachloride (SiCl4)
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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
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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.
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2d)
Na2Co3 + MgCl2 ----> 2NaCl + MgCo3
1mole 1mole 2mole 1mole
molar mass of Na2 Co3 = 2 * 23 + 12 * 1 + 16 * 3 = 46+12+48 = 106g
MM of MgCO3 = 24 + 12 + 16(3) = 84g/mol
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From equation of rnx, 1mol of Mgco3 requires 1mol of Na2Co3
84g -----------> 106g of Na2co3
1g -----------> 106/84
3.36 ----------> 106/84 x 3.36 = 4.24g
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5ai)
Na2S2O3 ===> 2 + 2x + 6 = 0
2x = 6 - 2 = 4
X = 4/2
X = 2
The oxidation number of sulphur is 2

(4ai)
calcium chloride, CaCl2
(4aii)
to the unknown substance 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

5aii)
Rhombic & monoclinic

5aiii)
- Both are tetravalent
- both are allotrope of carbon

5bi)
CO2 & Chloroflorocarbon
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5bii)
There is increase in sun radiation reaching the earths surface ie Global warming

5biii)
ThunderStorm

5iv)
I2KNo3. --------> 2KNO3 + O2
2AgNo3 --------->. 2Ag + 2No
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5ci)
Calcium chloride in a solution can give rise to crystal using filtera
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