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A 2.0 g sample of a mixture containing sodium carbonate, sodium bicarbonate and sodium sulphate is gently heated till the evolution of CO2 ceases. The volume of CO2 at 750 mm Hg pressure and at 298 K is measured to be 123.9 ml. A 1.5g of the same sample requires 150 ml. of (M/10) HCI for complete neutralization. Calculate the % composition of the components of the mixture.

Amit Saxena , 11 Years ago
Grade upto college level
anser 1 Answers
Navjyot Kalra

Last Activity: 11 Years ago

1.5 g of sample require = 150 ml. of M/10 HCI
∴ 2 g of sample require = 150/1.5 ml of M/10 HCI
= 200 ml. of M/10 HCI
On heating, the sample, only NaNCO3 undergoes decomposition as given below.
2NaHCO3 → Na2CO3 + H2O + CO2
2 moles 1 mole 1 mole
2 equ
Neutralization of the sample with HCI takes place as given below.
2NaHCO3 + HCI → NaCI + H2O + CO2
1 eq 1 eq
Na2CO3 + 2HCI → 2NaCI + H2O + CO2
1 mole 1 mole
2 eq 2 eq
Hence, 2 g sample ≡ 200 ml. of M/10 HCI
= 200 ml. of N/10 HCI = 20 meq = 0.020 eq
Number of moles of CO2formed, i.e.
N = PV/RT = 750/760 * 123.9/0.082 = 0.005
Moles of NaHCO3 in the sample (2 g) = 2 * 0.005 = 0.01
Equivalent of NaHCO3 = 0.01
Wt. of NaHCO3 = 0.01 * 84 = 0.84 g
% of NaHCO3 = 0.84 *100/2 = 42%
Equivalent of Na2CO3 = 0.02 – 0.01 = 0.01
Wt. of Na2CO3 = 0.01 * 53 = 0.53 g
∴ % of Na2CO3 = 0.53 *100/2 = 26.5%
∴ % of Na2SO3 in the mixture = 100 – (42 + 26.5) = 31.5%
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