Questions: What is the molarity of an HCl solution if 43.6 mL of a 0.125 M NaOH solution are needed to titrate a 25.0 mL sample of the acid according to the equation below (show your calculations)? NaOH(aq) + HCl(aq) → H2O(l) + NaCl(aq)

Solution Steps

The balanced chemical equation for the reaction is:

\[ \mathrm{NaOH}(aq) + \mathrm{HCl}(aq) \rightarrow \mathrm{H_2O}(l) + \mathrm{NaCl}(aq) \]

This equation shows a 1:1 molar ratio between NaOH and HCl.

To find the moles of NaOH used, use the formula:

\[ \text{moles of NaOH} = \text{molarity of NaOH} \times \text{volume of NaOH in liters} \]

Given:

• Molarity of NaOH = 0.125 M
• Volume of NaOH = 43.6 mL = 0.0436 L

\[ \text{moles of NaOH} = 0.125 \, \text{M} \times 0.0436 \, \text{L} = 0.00545 \, \text{mol} \]

Since the reaction is 1:1, the moles of HCl will be equal to the moles of NaOH:

\[ \text{moles of HCl} = 0.00545 \, \text{mol} \]

The molarity of HCl is calculated using the formula:

\[ \text{molarity of HCl} = \frac{\text{moles of HCl}}{\text{volume of HCl in liters}} \]

Given:

• Volume of HCl = 25.0 mL = 0.0250 L

\[ \text{molarity of HCl} = \frac{0.00545 \, \text{mol}}{0.0250 \, \text{L}} = 0.2180 \, \text{M} \]

Final Answer