2024 NABTEB CHEMISTRY: 2024 NABTEB CHEMISTRY ANSWERS (6731)

NABTEB CHEMISTRY
1-10: BCACBCBBDA
11-20: CBCACABAAA
21-30: CBBAABADAD
31-40: CABCDCDBBD
41-50: CBCAABACCD

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(1ai)
Chemical change is a change which is not easily reversible and in which entirely new substances are formed.

(1aii)
Differences between Chemical change and Physical Change
In a tabular form

Under CHEMICAL CHANGE:
(i) Entirely new substances are formed.
(ii) It is not easily reversible
(iii) Great heat changes are involved.

Under PHYSICAL CHANGE:
(i) No new substances are formed.
(ii) It is easily reversible.
(iii) Less heat changes are involved.

(1aiii)


A diagram for separating mixture of kerosene and water.

(1bi)
(i) Vanderwaal forces
(ii) Hydrogen bond

(1bii)
(i) Vanderwaal forces - Formation of molecular lattices as in iodine and naphthalene crystals
(ii) Hydrogen bond - Water, alkanols and some organic acids

(1biii)
H (-->Ionic bond)
| (-->Covalent bond)
H - N+ - Cl‐
/ |
H H


(1c)
Elements C O H
%comp 52.17 34.78 13.05
Ar 12 16 1

%comp/Ar 52.17/12 34.78/16 13.05/1
4.3475 2.1738 13.05

Ratio/smallest ratio
4.3475/2.1738 2.1738/2.1738 13.05/2.1738
1.999 1 6.00
2 1 6
The molecular formula is
C2OH6 = C2H6O = C2H5OH


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(2ai)
(i) No energy is gained or lost when gases collide.
(ii) The molecules in a gas take up a negligible amount of space compared to the volume of the container.

(2aii)
Sublimation.

(2aiii)
(i) Ammonium Chloride NH4Cl
(ii) iodine.

(2aiv)
R ∝ 1/√d, R = k/√d
Therefore, K = R√d
R1√d1 = R2√d2 => R1/R2 = √d2/√d1
Where R = Rate of diffusion, d = vapour density.


(2bi)
Increase in temperature will cause the equilibrium position to shift to the left, i.e It will favour the backward reaction.

(2bii)
Decrease in pressure will cause the equilibrium position of the system to shift to the left favouring the backward reactions. It will also result in high yields of the reactant.

(2biii)
Removal of oxygen will makes the equilibrium position to shift to the left, thereby, favouring the backward reactions. It will cause the equilibrium to shift to a new stable one.

(2ci)
CuSO4.2H2O --> Copper(ii)tetraoxosulphate(vi)dehydrate
OR
Na2CO3.NH2O - Sodiumtrioxocarbonate(iv)Pentahydrate

(2cii)
NaOH - Sodium hydroxide.
KOH - Potassium hydroxide.

(2ciii)
CaO - Calcium Oxide.
Conc H2SO4 - Concentrated tetraoxosulphate(vi)acid

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(3ai)
Hard water is any water that does not easily lather with soap due to the presence of dissolved salts in it.

(3aii)
(i) Permanent Hardness
(ii) Temporary hardness

-Permanent Hardness: Presnce of dissolved CaSO4 and MgSO4
-Temporary Hardness: Presence of dissolved Ca(HCO3)2 and Mg(HCO3)2

(3b) Advantages of hard water:
(i) Hard water taste better.
(ii) It helps in the formation of strong bones and teeth in children.

Disadvantages of hard water:
(i) It wastes soap.
(ii) Formation of deposits in pipes and furying of kettles and boilers.

(3ci) An ion is a positively or negatively charge atom or radical.

(3cii) Isotopes are atoms of the same amount with the same atomic number but different atomic masses.

(iii) Isotopes 35 37
Cl Cl
37 17
R/Abundance 75% 25%
R.A.M = (75×35/100) + (25×37/100)
=2625+925/100 = 3550/100
Relative atomic mass of chlorine = 35.5

(3d)
(i) H2SO4(aq) + 2NaCl(s) --> Na2SO4(aq) + 2HCl(g)
(ii) -It forms dense white fumes with NaOH(aq)
-It turns dense blue litmus paper red.



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(4)


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(5ai)
Polymerisation is the process whereby two or monomers link together to form a compound of high molecular mass called polymer.

(5aii)
(i)Natural polymers; silk,wool,DNA,Cellulose
(ii)Artificial polymer; cellulose acetate, viscose rayon

(5bi)
Heavy chemical industry: It is a term that applies to such products as the common acids,soda,ash, caustic soda and those salts and other chemicals that are produced by an industry in large quantities and at relatively little cost

(5bii)
(i)Availability of raw materials
(ii)Transportation facility
(iii)Regular power supply

(5biii)
-Raw materials for cement industry -
(i)Limestone
(ii)Shells
(iii)Chalk
(iv)Marl combined with shale ,clay,slate,blast furnace slag, silica sand and iron ore

- Raw materials for soap industry -
(i)Fat
(ii)Alkali
(iii)Sodium hydroxide
(iv)Potassium hydroxide

(5ci)
Saponification: It is the hydrolysis of fats and oils with caustic alkali yields propane-1,2,3-triol and the corresponding sodium and potassium salts of the component fatty acids.These salts are the principal constitutes of soaps.

(5cii)
Plant matter, such as plantain skins,palm tree leaves, cocoa pods and Shea tree bark,is first sun -dried and then burned to produce Ash (which supplies the alkali required to convert or saponify the oils and fats). Next ,water and various oils and fats such as coconut oil,palm oil and shea butter are added to the ash. The mixture is cooked and hand-stirred for at least 24 hours. After the soap solidifies,it is scooped out and set out to cure.

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