JAMB Chemistry Past Questions & Answers

2,161.

Which of the following gases will diffuse fastest when passed through a porous plug?
[H = 1, C = 12, N = 14, O = 16]

Propane

Oxygen

Methane

Ammonia

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

2,162.

56.00cm³ of a gas at S.T.P. weighed 0.11g. What is the vapour density of the gas?
[Molar volume of a gas at S.T.P = 22.4dm³]

11.00

22.00

33.00

44.00

View answer & explanation

Correct answer is B

56.00cm³ of a gas at S.T.P weighed 0.11g
Molar volume of the gas = 22.4dm3 = 22400cm3
molar mass = (22400 x 0.11)/56
molar mass = 2464/56 = 44
Vapour density = Molar mass/2 = 44/2 = 22

2,163.

200cm3 each of 0.1M solutions of lead (II) trioxonitrate(V) and hydrochloric acid were mixed. Assuming that lead (II) chloride is completely insoluble, calculate the mass of lead (II) chloride that will be precipitated.
[Pb = 207, Cl= 35.5, N = 14, O = 16]

2.78g

5.56g

8.34g

11.12g

View answer & explanation

Correct answer is A

HCl + Pb(NO3)2 ===> 2HNO3 + PbCl2
2moles of HCl ===> 1mole of PbCl2

n = CV/1000 = (100 x 0.2)/(1000) = 0.02 mol
n (HCl) = 0.02 mol

2 moles of HCl ===> 1 mole of PbCl2
0.02 mole of HCl ===> x mole of PbCl2
2x = 0.02
x = 0.01 mol

n = m/M
m = 0.01 x (207 + (35.5 x 2)) = 0.01 x 278 = 2.78 g note; HCl is used for the calculation instead of lead(II) nitrate because it is the limiting reactant meaning it will be used up first before lead(11) nitrate