Question

A 878 mL aqueous solution contains 0.0314 mol of HCl. What is the pH? Give your answer to 3 significant figures.

Answer 1

Answer to the Question #47302 - Chemistry - Other

Question

A 878 mL aqueous solution contains 0.0314 mol of HCl. What is the pH? Give your answer to 3 significant figures.

Answer:

Molar concentration of this solution is:

$$C = \frac{n}{V} = \frac{0.0314}{0.878} = 0.036 \, \text{mol/L}$$

n – Number of moles of HCl, n = 0.0314 mol.

V – Volume of the solution, V = 878 mL = 0.878 L.

pH equals:

$$\mathrm{pH} = -\lg [\mathrm{H}^{+}]$$

$[\mathrm{H}^{+}]$ – Molar concentration of $\mathrm{H}^{+}$ ions.

Hydrochloric acid is a strong acid and it fully dissociates in water:

$$\mathrm{HCl}_{(\mathrm{aq})} \leftrightarrow \mathrm{H}^{+}_{(\mathrm{aq})} + \mathrm{Cl}^{-}_{(\mathrm{aq})}$$

We see that the concentration of $\mathrm{H}^{+}$ ions is equal to the concentration of HCl. Therefore $\mathrm{H}^{+}$ ion concentration is:

$$[\mathrm{H}^{+}] = \mathrm{C}(\mathrm{HCl}) = 0.036 \, \text{mol/L}$$

So, pH value of 0.036 M HCl is:

$$\mathrm{pH} = -\lg (0.036) = 1.444$$

Answer: $\mathrm{pH} = 1.444$