Bright Tutorials Bright Tutorials
ICSE Class 10 Chemistry Question 31 of 72

Mole Concept & Stoichiometry Miscellaneous Exercises — Question 31

Back to all questions
31
Question

Question 30

Washing soda has formula Na2CO3.10H2O. What mass of anhydrous sodium carbonate is left when all the water of crystallization is expelled by heating 57.2 g of washing soda?

Answer

Na2CO3.10H2O→ΔNa2CO3+10H2O2(23)+12+3(16)2(23)+1210[2(1)+10[2(1)+16]+3(16)+16]=46+12+48=46+12=180 g+10(18)+48=286 g=106 g\begin{matrix} \text{Na}_2\text{CO}_3.10\text{H}_2\text{O} & \xrightarrow{\Delta} & \text{Na}_2\text{CO}_3 & + & 10\text{H}_2\text{O} \\ 2(23) + 12 + 3 (16) & & 2(23) + 12 & & 10[2(1) \\ + 10[2(1) + 16] & & + 3(16) & & + 16] \\ = 46 + 12 + 48 & & = 46 + 12 & & = 180 \text{ g} \\ + 10(18) & & + 48 \\ = 286 \text{ g} & & = 106 \text{ g} \\ \end{matrix}

286 g of washing soda had 106 g of anhydrous sodium carbonate

∴ 57.2 g will have = 106286\dfrac{106}{286} x 57.2 = 21.2 g anhydrous sodium carbonate.

Hence, 21.2 g anhydrous sodium carbonate is left.