2020 Nabteb Chemistry Answers

2020 Nabteb Chemistry Answers

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Theory:

INSTRUCTION: Answer four (4) Questions in all

NUMBER 1⃣2⃣3⃣4⃣5⃣ SOLVED

(1ai) 

Chemical change is a permanent change and it cannot be easily reversed. 

(1aii) 

PHYSICAL CHANGE 

(i) It is easily reversible. 

(ii) New substance are not formed. 

(iii) No change in mass. 

CHEMICAL CHANGE 

(i) It is not easily reversed. 

(ii) New substance are formed.Port) The new substance always have different masses. 

(1aiii) 

(View image above)

 (1bi) 

(i) Van der wale force. 

(ii) Hydrogen bond. 

(1bii) 

(i) Van der waale force e.g oxygen. 

(ii) Hydrogen bond e.g HF.  

(1c) 

Carbon (C)=52.17%

Oxygen (O)=34.78%

Hydrogen (H)=100 - (52.17 + 34.78)

=100 - 86.95

=13.05%

TABULATE 

C || H  || O

Percentage Abundance 52.17/12  || 13.05/1 || 34.78/16

4.3475/2.17375 || 13.05/2.17375 || 2.17375/2.17375

2 || 6.00 || 1

Empirical formula=C2H6O. 

(C2H6O)n=Relative molecular mass

[(12×2) + (1×6) + (16×1)]n=46

(24+6+16)n=46

46n=46

Divide both sides by 46

n=1

(C2H6O)n=(C2H6O)1

=C2H6O

:. The molecular formular is C2H6O. 

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(2ai) 

(Pick any two) 

(i) The particles do not attract each other. 

(ii) Gases are made up of molecules which are in constant motion. 

(iii) The collision of the gas molecules are perfectly elastic. 

(iv) The temperature of the gas is a measure of the average Kinetic energy of the gas particles. 

(2aii) 

Sublimation

(2aiii) 

(i) Sulphur. 

(ii) Iondine. 

(2aiv) 

R is directly proportional to 1/√p

Where R is the rate of diffusion of gas. 

p is the vapour density of gas

(2b) 

2SO2(g) + O2(g) <——> 2SO3(g) 

∆H= -xKJ/mol

(i) Increase in temperature :- In this case, the forward reaction is exothermic. Therefore, an increase in temperature will cause the equilibrium position to shift to the left i.e it favours reactant formation(SO2 & O2)

(ii) Decrease in Pressure :- Decrease in pressure cause the equilibrium position to shift to the left, favouring the backward reaction. This will cause an increase in the pressure of the system and thus keep the equilibrium constant unchanged. It will also result in high yields of the reactants(SO2 & O2). 

(iii) Removal of oxygen :- Removal of oxygen will shift the equilibrium position to the left thereby favouring the backward reaction. Removal of oxygen favours the reactants. 

(2ci) 

Sodium tetraoxosulphate(iv) decahydrate (Na2CO3•IOH2O) 

(2cii) 

(Pick any one) 

(i) Calcium chloride (CaCl2). 

(ii) Potassium Hydroxide (KOH). 

(iii) Magnesium Chloride (MgCl2). 

(2ciii) 

(Pick any one) 

(i) Copper(ii) Oxide (CuO). 

(ii) Sodium Trioxonitrate(v) (NaNO3). 

(iii) Calcium Oxide. 

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(3ai) 

Hard Water do not form ladder readily with soap. It is a water that contains a number of dissolved salts which include CaSO4, MgSO4 and Ca(HCO3)2 

(3aii) 

(i) Temporary hardness of water

(ii) Permanent hardness of water

Permanent hardness of water is caused by calcium tetraoxosulphate(vi) salts or magnesium tetraoxosulphate(vi) salts  WHILE Temporary hardness of water is caused by hydrogen trioxocarbonate(v) salt.

(3b) 

ADVANTAGES

(Pick any 2)

(i) It tastes better than soft water due to presence of dissolved minerals in it. 

(ii) Calcium salts present in it, when  taken by animals help to build strong bones and teeth. 

(iii) Helps in formation of shells in Snails and crab. 

DISADVANTAGES 

(Pick any 2)

(i) It wastes soap. 

(ii) It causes furing in kettles and pipes.  

(iii) It cannot be used in tanning and dyeing industries as Ca^2+ ions and Mg^2+ ions interfere in the process.  

(3ci) 

An ion Is any atom or group of atom which posses an electric charge. 

(3cii) 

Isotope is the existence or phenomenon whereby atom of the same element having the same atomic number but different mass number due to difference in the number of neutron present in those atom. 

(3ciii) 

35                        37

Cl                         Cl

17                        17

=(75/100 × 35) + (25/100 × 37)

=26.25 + 9.25

=35.5

(3di) 

2NaCl + H2SO4 ———> Na2SO4 + 2HCl(g) 

(3dii) 

(i) Colourless gas with an irritating smell. 

(ii) Damp blue litmus paper turns red. 

(iii) 1.25 times denser than air. 

(iv) Very soluble in water.

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(4ai) 

(View image above) 

(4aii) 

(Pick any one) 

(i) Starch-iodide paper test. 

(ii) Damp blue litmus paer test. 

(4bi) 

(i) 2FeCl2(aq) + Cl2(g) ——> 2FeCl3(aq).  

(ii) 2KI(aq) + Cl2(g) ——> 2KCl(aq) + I2(s). 

(iii) 6NaOH(aq) + 3Cl2(g) ——> NaClO3(aq) + 5NaCl(aq) + 3H2O(l). 

(4ci) 

Number of electrons=2n²

In M shell, n=3

:. 2n² = 2(3)²

=2×9

=18

(4cii) 

(View image above) 

(4ciii) 

(Pick any three) 

(i) It has hard and brittle solid. 

(ii) It readily dissolve in water. 

(iii) It has high melting and boiling point.

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