JAMB Chemistry Past Questions & Answers - Page 310

1,546.

Calculate the volume of carbon (IV)oxide measured at s.t.p, produced when 1 kg of potassium hydrogen trioxocarbonate (IV) is totally decomposed by heat?

(G.M.V. at s.t.p 22.4 dm³, K = 39, O = 16, C = 12, H = 1)

28 dm³

56 dm³

112 dm³

196 dm³

View answer & explanation

Correct answer is C

2KHCOdm₃ → K₂CO₃ + H₂O + CO₂
2(39 + 1 + 12 + 48) 22.4 dm³
200 g 22.4 dm³ of CO₂
1000 g (1000) / (200) x 22.4 = 112 dm³

1,547.

30cm\(^3\) of oxygen at 10 atmospheres pressure is placed in a 20 cm\(^3\) container. Calculate the new pressure if temperature is kept constant?

6.7 atm

15.0 atm

60.0 atm

66. 0 atm

View answer & explanation

Correct answer is B

P\(_1\)V\(_1\) = P\(_2\)V\(_2\) (where T is kept constant)

30 x 10 = P\(_2\) x 20

P\(_2\) = \(\frac{30 \times 10}{20}\)

= 15.0 atm

1,548.

In two separate experiments, 0.36g and 0.71g of chlorine combined with a metal X to give Y and Z respectively. An analysis showed that Y and Z contain 0.20g and 0.40g of X respectively. The data above represents the law of ?

multiple proportion

conservation of mass

constant composition

reciprocal proportion

View answer & explanation

Correct answer is C

0.36g of Cl combines with 0.2g of x

1g of Cl will combine with \(\frac{1 \times 0.2}{0.32}\) = 0.56

0.71g of U combines with 0.49g of x

1g of U will combine with \(\frac{1 \times 0.4}{71}\) = 0.56

Ratio 0.56 : 0.56 = 1:1

1,549.

An iron ore is known to contain 70.0% Fe₂O₃. The obtain from 80kg of the ore is?

(Fe = 56, O = 16)

35.0 kg

39.2 kg

70.0 kg

78.4 kg

View answer & explanation

Correct answer is B

2Fe₂O₃ → 4Fe + 3O₂
320g 224g 96g
(70) / (100) x (80) / (1) 56g
if 0.32kg of Fe₂9₃ contains 0.224 kg
Then 56kg will contain (56 x 0.224) / (0.32) =39.2 kg