Acid–base neutralization reactions Transitional Reasoning Download PDF

Questions

1. 1.

   An industrial neutralization process combines 300.0 mL of 0.450 M $\text{KOH(aq)}$ with 150.0 mL of 0.300 M $\text{H}_3\text{PO}_4\text{(aq)}$ to produce potassium phosphate and water according to the reaction $3\text{KOH(aq)} + \text{H}_3\text{PO}_4\text{(aq)} \rightarrow \text{K}_3\text{PO}_4\text{(aq)} + 3\text{H}_2\text{O(l)}$. Assuming the solution volumes are strictly additive, what is the molar concentration of $\text{K}_3\text{PO}_4$ in the resulting neutral solution?

   • A) 0.100 M
   • B) 0.150 M
   • C) 0.300 M
   • D) 0.0500 M
2. 2.

   A pharmaceutical quality-control chemist analyzes an antacid tablet with a total mass of 2.00 g containing $\text{Mg(OH)}_2$ as its sole active neutralizing agent. The tablet is crushed and completely reacted with 100.0 mL of 0.500 M $\text{HCl(aq)}$, leaving an excess of unreacted acid. The remaining unreacted acid is then completely neutralized by titrating with 20.0 mL of 0.500 M $\text{NaOH(aq)}$. Given that the molar mass of $\text{Mg(OH)}_2$ is 58.3 g/mol, what is the mass percentage of $\text{Mg(OH)}_2$ in the antacid tablet?

   • A) 14.6%
   • B) 29.2%
   • C) 72.9%
   • D) 58.3%
3. 3.

   To determine the identity of an unknown solid diprotic acid ($\text{H}_2\text{A}$), a student dissolves a 0.450 g sample in distilled water. The resulting solution is titrated to the equivalence point using 30.0 mL of a 0.250 M $\text{NaOH}$ solution according to the balanced reaction $\text{H}_2\text{A(aq)} + 2\text{NaOH(aq)} \rightarrow \text{Na}_2\text{A(aq)} + 2\text{H}_2\text{O(l)}$. Based on these experimental results, what is the molar mass of the diprotic acid?

   • A) 30.0 g/mol
   • B) 60.0 g/mol
   • C) 240 g/mol
   • D) 120 g/mol
4. 4.

   A laboratory technician must neutralize 500.0 mL of wastewater containing 0.120 M phosphoric acid, $\text{H}_3\text{PO}_4$, prior to disposal. Solid calcium hydroxide, $\text{Ca(OH)}_2$ (molar mass = 74.10 g/mol), is added to carry out the neutralization according to the following balanced equation: $2\text{H}_3\text{PO}_4\text{(aq)} + 3\text{Ca(OH)}_2\text{(s)} \rightarrow \text{Ca}_3(\text{PO}_4)_2\text{(s)} + 6\text{H}_2\text{O(l)}$ What minimum mass of pure $\text{Ca(OH)}_2$ is required to completely neutralize the phosphoric acid present in this sample?

   • A) 2.96 g
   • B) 4.45 g
   • C) 13.3 g
   • D) 6.67 g
5. 5.

   A student investigates an acid–base neutralization by mixing 40.0 mL of 0.150 M $\text{H}_2\text{SO}_4$ with 60.0 mL of 0.150 M NaOH. The reaction proceeds according to the balanced equation $\text{H}_2\text{SO}_4\text{(aq)} + 2\text{NaOH(aq)} \rightarrow \text{Na}_2\text{SO}_4\text{(aq)} + 2\text{H}_2\text{O(l)}$. Which reactant remains in excess after the reaction reaches completion, and what amount of this excess reactant is left unreacted?

   • A) NaOH is in excess, with $3.00 \times 10^{-3}$ mol remaining.
   • B) NaOH is in excess, with $1.50 \times 10^{-3}$ mol remaining.
   • C) $\text{H}_2\text{SO}_4$ is in excess, with $4.50 \times 10^{-3}$ mol remaining.
   • D) $\text{H}_2\text{SO}_4$ is in excess, with $1.50 \times 10^{-3}$ mol remaining.