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waec 2025 chemistry questions and answers



EXAM: WAEC  2025

SUBJECT: chemistry

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CHEMISTRY OBJ

1-10: ABAABDACCB

11-20: BACAABDACC

21-30: BBBCDABDBA

31-40: DDABDCADDB

41-50: DADBAAAABA

 Completed

  







(5ai)
Producer gas

(5aii)
(i) Carbon monoxide (CO) 
(ii) Nitrogen (N₂)

(5aiii)
Because carbon monoxide (CO) and nitrogen (N₂) have almost the same relative molecular masses (CO = 28, N₂ = 28), so they diffuse at the same rate according to Graham's law of diffusion.

(5aiv)
Nitrogen (N₂)

(5av)
Nitrogen is diatomic and has a strong triple bond (N≡N), which makes it very stable and less reactive under normal conditions.

(5bi)
2Na + 2H₂O → 2NaOH + H₂

(5bii) 
Fe₂O₃ + 3CO → 2Fe + 3CO₂

(5biii) 
The temperature in the blast furnace decreases from bottom to top because the bottom is where hot air is blasted in and coke burns, producing a lot of heat. As gases rise, they lose heat to the raw materials coming down, so the top is cooler.

(5c)
In a Tabular form

-PRODUCT-
(i) Ammoniacal liquor
(ii) Coal tar
(iii) Coke
(iv) Coal gas

-USE-
(i) Manufacture of fertilizer
(ii) Road surfacing / production of dyes, drugs, explosives, etc.
(iii) Production of water gas
(iv) Fuel / lighting and heating

(5di)
(i) Al(OH)₃: Used in the manufacture of fireproofing materials or antacid production.
(ii) KAl(SO₄)₂: Used in water purification (as a coagulant).
(iii)Na₃AlF₆: Used in the electrolytic extraction of aluminium (Hall–Héroult process).

(5dii)
(i) Acts as a flame retardant or used as a precipitating agent in water treatment.
(ii) Used as a coagulant in the purification of water, helping to clump together fine particles so they can be filtered out.
(iii) Used as a flux in the electrolysis of aluminium ore (bauxite) to lower the melting point of aluminium oxide.

(5diii)
Potassium aluminium sulfate



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