Question

What is the pH of a 0.025M solution of hydrochloric acid?

1. 16.0
2. 3.68
3. 0.16
4. 1.60
5. 0.025

How do I work this out?

Answer 1

Answer on Question #43447 - Chemistry – Inorganic Chemistry

Question:

What is the pH of a 0.025M solution of hydrochloric acid?

1. 16.0

2. 3.68

3. 0.16

4. 1.60

5. 0.025

How do I work this out?

Answer:

1. pH equals:

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

$\left[\mathrm{H}^{+}\right]$ – 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:

$$\left[ \mathrm{H}^{+} \right] = \mathrm{C}(\mathrm{HCl}) = 0.025 \mathrm{M} = 0.025 \mathrm{mol/L}$$

So, pH value of 0.025 M HCl is:

$$\mathrm{pH} = -\lg (0.025) = 1.60$$

Answer: (4): $\mathrm{pH} = 1.60$

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