Question

What is the pH of a 4.2 x 10^-3 solution of HCl?

Answer 1

HCl + H
`\\ 2`O —> Cl- + H
`\\ 3`O+

pH = -log [H
`\\ 3`O+] = -log [4.2 x 10^-3] = 2.38

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We assume that hydrochloric acid will undergo complete dissociation in water to give stoichiometric H3O+ ion, according to the given reaction.

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Answer 2

pH = 2.38

Step-by-step explanation:

Recall that HCl is a strong acid and hence dissociates completely into H⁺ and Cl⁻ ions. Thus, the solution's H⁺ concentration is equivalent to the acid concentration. That is, [H⁺] = 4.2 × 10⁻³ M.

Therefore, the pH of the solution is:

`\displaystyle \begin{aligned}\text{pH} & = -\log[\text{H}^+] \\ \\ & = -\log (4.2* 10^(-3)) \\ \\ & = 2.38\end{aligned}`