Chemistry

Calculate
(i) The volume of 2.5 moles of a gas X at stp.
(ii) The weight of 2.8 dm³ of a basic gas you have learnt, at STP.
(iii) The molecular weight of a gas Y whose 5.6 litres of volume at STP weighs 3.5 gms.
(at wt of C = 12, X = 14, H = 1, O = 16)

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(i) Vol. occupied by 1 mole = 22.4 lit

∴ Vol. occupied by 2.5 moles = 22.4 x 2.5 = 56 lit.

Hence, vol. occupied is 56 lit.

(ii) Let the basic gas be NH₃

Molecular mass of NH₃ = 14 +3(1) = 17 g

At STP, 1 mole of ammonia weighs 17 g and occupy 22.4 dm³ volume.

∴ 1 dm³ volume has weight = $\dfrac{17}{22.4}$ = 0.76 g

∴ 2.8 dm³ of NH₃ has weight = 2.8 x 0.76 = 2.128 g

Hence, weight of 2.8 dm³ of ammonia = 2.128 g

(iii) 5.6 L of volume at STP weighs 3.5 gms.

∴ 22.4 L of volume weighs = $\dfrac{3.5}{5.6}$ x 22.4 = 14 g

Hence, molecular weight = 14g

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