JAMB Chemistry Past Questions & Answers - Page 300

1,496.

The electronic configuration of an elements is 1s22s22p63s23p3. How many unpaired electrons are there in the element?

A.

5

B.

4

C.

3

D.

2

Correct answer is C

The atomic number of phosphorus is 15 and the 3p sublevel has three unpaired electrons.

1,497.

Atoms of element X (with 2 electrons in the outer shell). combine with atoms of Y (with 7 electrons in the outer shell). Which of the following statements is FALSE? The compound formed?

A.

has formula XY

B.

is likely to be ionic

C.

contains X2+ ions

D.

contains Y- ions

Correct answer is A

The compound formed by a mixture of X and Y will be \(XY_{2}\) not XY.

1,498.

A sample of a gas exerts a pressure of 8.2 atm when confined in a 2.93 dm3 container at 20°C. The number of moles of gas in the sample is?

(R = 0.082 litre atm / deg mole)

A.

1.00

B.

2.00

C.

3.00

D.

4.00

Correct answer is A

PV = nRT
2.93 x 8.2 = 0.082 x 293 xn
∴ n = (2.93 x8.2) / (0.082 x 293)
n = 1

1,499.

A given quantity of a gas occupies a volume of 228 cm3 at a pressure of 750mm Hg. What will be its volume at atmospheric pressure?

A.

220 cm3

B.

225 cm3

C.

230 cm3

D.

235 cm3

Correct answer is B

P1V1 = P2V2 ∴ 750 x 228 = 760 V2
V2 = (750 x 228 cm3) / (760) = 225 cm3

1,500.

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)

A.

28 dm3

B.

56 dm3

C.

112 dm3

D.

196 dm3

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