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2020 NABTEB CHEMISTRY OBJ AND ESSAY QUESTIONS AND ANSWERS

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NABTEB CHEMISTRY OBJ

1-10: BCACCCBBDA

11-20: CCCACABACA

21-30: CBCAABACAD

31-40: CABCDCDBBA

41-50: CBDDABADCD

 

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

(1ai)
A chemical change is one which is not easily reversed and in which new substances are formed

(1aii)
– CHEMICAL CHANGE –
(i) It is not easily reversible
(ii) Entirely new substances are always produced
(iii) There’s is a change in the mass of a substance that undergoes such a change

– PHYSICAL CHANGE –
(i) It is easily reversed
(ii) No new substances are formed
(iii) There is no change in the mass of a substance involved in such a change

(1aiii)


(1bi)
(i)Van der Waals forces
(ii)Hydrogen bond

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

(1biii)


H
|
H -N- Cl
/ |
H H

(1c)

(1c)
C
52.17%/12

4.35/2.17
2

O
34.78%/16

2.17/2.17
1

H
13.05/1

13.05/2.17
6

(C2HO6)n = 46
(12×2+16+1×6)n = 46
( 24+16+6)n = 46
46n = 46
n= 46/46 =1
(CHO)1 = CHO
=====================================

(2ai)
(i)The gas molecules move randomly in straight lines colliding with one another and with the walls of the container
(ii)The collision of the gas molecules are perfectly elastic

(2aii)
Sublimation

(2aiii)
(i)Iodine
(ii)Ammonium chloride

(2aiv)
R ∝ 1/√P , R1/R2 = √P2/P1

(2bi)
Increase in temperature will cause the equilibrium position to shift to the left, i.e it favours reactant formation.

(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. It will cause the equilibrium to shift to a new stable one.

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(2c)
(i) Na2CO3.10H2O(s) –> Na2.CO3H2O(s) + 9H2O(g) – CaSO4
(ii) NaOH, CaCl2, Fecl3
(iii) NaNo3, CUO
=====================================

(3ai)
Hard water is the water that does not form lather readily with soap,it contains a number of dissolved salts, calcium tetraoxosulphate(vi), magnesium tetraoxosulphate(vi) and calcium hydrogentrioxocarbonate(iv)

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

(a) presence of dissolved calcium hydrogentrioxocarbonate (iv) Ca(HCO3)2
(b) presence of calcium and magnesium ions in the form of soluble tetraoxosulphate(iv) and chlorides

(3b)
-Advantages of hard water –
(i)it tastes better soft water because of the dissolved minerals in it.
(ii)The calcium salts present in hard water when taken in by animals help to build strong teeth and bones.

– Disadvantages of hard water –
(i)It requires a lot of soap before it can form a latter
(ii)It causes furring of kettles and boilers

(3ci)
Ion is any atons atom or group of atoms which posses an electric charge

(3cii)
Isotope is one or two or more species of atoms of chemical element with the same atomic number and position in the periodic table and nearly identical chemical behaviour but with different atomic masses and physical properties

(3ciii)
(75/100 × 25) + (25/100 × 37)
= 26.25 + 9.25 = 35.5

(3di)
(i)Nacl(s) + H2SO4(aq) —> NaHSO4(aq) + HCl(g)

(ii)Nacl(s) + NaHSO4(aq) –> NaSO4(aq) + Hcl(g)

(iii)2Nacl(s) + H2SO4(aq) –> NaSO4(aq) + 2Hcl(g)

(3dii)
(i)It is a colourless gas with a sharp irritating smell
(ii)It turns damp blue litmus paper red, showing that it is acidic in aqueous solution
=====================================

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

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(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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