2025 NECO GCE CHEMISTRY: 2025 NECO GCE CHEMISTRY QUESTIONS AND ANSWERS (3156)

(3ai)
A flame is a region where gases combine chemically with the production of heat and light

(3aii)
Oxygen is neutral to litmus paper

(3aiii)
NaCO2(aq) + CaSO4(aq) --> CaCO3(s) + Na2SO4(aq)
The addition of washing soda removes the calcium ions as the insoluble calcium carbonate

(3aiv)
Ammonia is trigonal pyramidal in shape

(3bi)
2Acl(s) + 6H2SO4(aq) --> Al2(SO4)3(aq) + 6H2O(l) + 3SO2(g)

(3bii)
No. of moles of Al = 3/27 = 1/9moles
No of moles of SO2 produced = 3/2 * 1/9
= 1/6moles
1 mole = 22.4dm³
1/6moles produces 1/6*22.4dm³ of SO2
= 3.733dm³

(3ci)
(i) Deuterium
(ii) Tritium

(3cii)
(i)Hydrogen is colourless and tasteless
(ii)It is neutral to most litmus paper

(3ciii)
(i) Hydrogen peroxide is used as an antiseptic
(ii)It is used in bleaching delicate materials such as silk

(3civ)
Insert a brightly glowing splinter into a test tube containing either of the gases, the splinter is rekindled

(3di)
(i) Presence of oxygen
(ii) Presence of water

(3dii)
SiO2(s) + CaO(s) --> CaSiO(s)

(3diii)
(i)Excretion
(ii)Industries

(3)

(4ai)
A chemical change is one which is not reversible

(4aii)
Na2CO3.10NH2O
= 2(23)+12+3(16)+10[2(1)+16]
= 46+12+48+180
= 286

(4aiii)
3Cu(s)+8HNO3(aq) --> 3Cu(NO3)2(aq) + 4H2O(l)
Action at 50% acid solution and copper turnings

(4bi)
I - Zn(s) + 2HCl(aq) --> ZnCl2(aq) + H2(g)
II - X is Zinc chloride
Y is hydrogen gas
III - X is used for ;
(i) Petroleum refining
(ii) As an electrolyte

(4bii)
(i) Roasting the room ore to give iron III oxide
(ii) Oxidation of coke to CO2
(iii) Reduction of CO2 to CO by coke
(iv) Reaction of CO with Iron III oxide to give iron

(4ci)
2*96500 = 63.5
0.5*t = 0.25
t = 2*96500*0.25/0.5*63.5
t = 1519.685sec
t = 25.33minutes

(4cii)
Electroplating is a method of coating the surface of one metal with another metal, usually copper, silver, chromium, nickel, or gold by means of electrolysis for decoration or protection against corrosion

(4ciii)
(i) Calcium oxide is used in the manufacture of slake lime
(ii) In agriculture, lime is used to treat acidic soils

(5ai)

Electrolysis is defined as the process of using electricity to separate chemical compounds, causing the chemical reaction of oxidation-reduction to occur. 

(5aii)

- Electrolytes are decomposed by the passage of electric current while Conductors are not decomposed by electric current

- Electrolytes are aqueous solution/ molten salts while Conductors are usually solid

(5b)

(5ci)

- Coke

- Coal 

(5cii)

- Used in fire extinguishers 

- Used as a refrigerating agent for perishable goods

(5ciii)

- carbon monoxide

- hydrogen gas.

(6ai)
(i)Diamond
(ii)Graphite

(6aii)
(i)Diamond is a 3-dimensional octahedral crystal
(ii) Graphite is a 2-dimensional hexagonal crystal

(6aiii)

(6bi)
(i) fats have high melting point
(ii) Oil can be hydrogenated to give fat

(6bii)
(i) Hydrogenation
(ii) Saponification

(6biii)
H H H H
| | | |
H -C - C C C -H
| | | |
H H H H

(6biv)
Pentane => C5H12
% hydrogen = 12(H)/12(H) + 5(C) *100/1
= 12/12+60 *100/1
= 12/72 * 100%
= 0.1667*100%
= 16.67%

(6ci)
Amphoteric oxides are oxides which behave as both basic and acidic oxides

(6cii)
Al2O3(s) + 6HCl(aq) ---> 2AlCl3(s) + 3H2O(l)

(6ciii)
Solubility = Mass/Molar mass * 100/volume
= 50/105 * 1000/200
= 2.38mol/dm³

(6a)

(6aiii)

(6c)