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ICSE Class 10 Chemistry Question 39 of 72

Mole Concept & Stoichiometry Miscellaneous Exercises — Question 39

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Question 38

10 g of a mixture of sodium chloride and anhydrous sodium sulphate is dissolved in water. An excess of barium chloride solution is added and 6.99 g of barium sulphate is precipitated according to the equation given below:

Na2SO4 + BaCl2 ⟶ BaSO4 + 2NaCl

Calculate the percentage of sodium sulphate in the original mixture.

Answer

Na2SO4+BaCl2⟶BaSO4↓+2NaCl2(23)+32137+32+4(16)+4(16)=46+32=137+32+64+64=142 g=233 g\begin{matrix} \text{Na}_2\text{SO}_4 & + & \text{BaCl}_2 & \longrightarrow & \text{BaSO}_4 \downarrow & + & 2\text{NaCl} \\ 2(23) + 32 & & & & 137 + 32 \\ + 4(16) & & & & + 4(16) \\ = 46 + 32 & & & & = 137 + 32 \\ + 64 & & & & + 64 \\ = 142 \text{ g} & & & & = 233 \text{ g} \\ \end{matrix}

233 g of BaSO4 is obtained from 142 g of Na2SO4

6.99 g of BaSO4 will be obtained from 142233\dfrac{142}{233} x 6.99 = 4.26 g of Na2SO4.

∴ In 10 g mixture 4.2610\dfrac{4.26}{10} x 100 = 42.6% Na2SO4 is present.

Hence, 42.6% Na2SO4 is present in the original mixture