Ten grams of calcium carbonate which is only 90% pure is treated with excess hydrochloric acid. What is the mass of $CO_{2}$ gas liberated? (Atomic mass: $Ca=40$, $C=12$ & $O=16$) ________.
Show Hint
Always calculate based on the pure weight of the reactant.
Step 1: Concept
Determine the amount of pure reactant and use stoichiometry.
Step 2: Meaning
Pure $CaCO_3 = 90\% \text{ of } 10g = 9g$. Molar mass of $CaCO_3 = 100g/mol$; Molar mass of $CO_2 = 44g/mol$.
Step 3: Analysis
Reaction: $CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2$. 100g $CaCO_3$ gives 44g $CO_2$.
Mass of $CO_2 = \frac{44}{100} \times 9$.
Step 4: Conclusion
Mass $= 3.96g$.
Final Answer: (B)