AP Chemistry 1.1 Moles and Molar Mass- MCQs - Exam Style Questions
▶️ Answer/Explanation
1. Assume 100 g sample:
S: \( 40\, \text{g} \), O: \( 60\, \text{g} \)
2. Calculate moles:
S: \( \frac{40}{32.06} = 1.25\, \text{mol} \)
O: \( \frac{60}{16.00} = 3.75\, \text{mol} \)
3. Find mole ratio:
\( \frac{1.25}{1.25} : \frac{3.75}{1.25} = 1 : 3 \)
4. Empirical formula:
\( \text{SO}_3 \)
✅ Answer: (A)
Questions
Another sample of eggshell reacts completely with 4.0 mL of an HCl(aq) solution of unknown concentration. If the reaction produced 0.095 atm of gas, the concentration of the HCl(aq) solution was at least
(A) 0.0020 M
(B) 0.050 M
(C) 0.50 M
(D) 1.0 M
▶️Answer/Explanation
Ans: D
\(P=0.095\) atm \(\rightarrow\) corresponds to \(0.20 \mathrm{~g} \mathrm{CaCO}_3\)
So, moles of \(\mathrm{CaCO}_3=\frac{0.20 \mathrm{~g}}{100 \mathrm{gm}{mol}^{-1}}=0.002 \mathrm{moles}\)
moles of \(\mathrm{HCl}=\left(\right.\) moles of \(\left.\mathrm{CaCO}_3 \times 2\right) \Rightarrow 0.002 \times 2\)
So, molarity of \(\mathrm{HCl}=\frac{\text { moles }}{\text { Volume in } \mathrm{L}} \Rightarrow \frac{0.004}{4} \times 1000\)
Concentration of \(\mathrm{HCl}=1 \mathrm{~m} \rightarrow\) option \((\mathrm{D})\)
Questions
The mass percent of \(CaCO_{3}\)(s) in the eggshell is closest to
(A) 30%
(B) 45%
(C) 60%
(D) 75%
▶️Answer/Explanation
Ans: D
(36) Pressure of gas \(=0.870-0.800=0.07 \mathrm{~atm}\) Mass of \(\mathrm{CaCO}_3\) corresponding to it \(\Rightarrow 0.15 \mathrm{~g}\) (approx)
So, \(\% \mathrm{CaCO}_3=\frac{0.15}{0.20} \times 100 \Rightarrow 75 \%\)