Question

1. hydrochloric acid (hcl), a strong acid, is added to a beaker of pure water.

a. what is the ph of the pure water in the beaker before the acid is added?
b. how does the hydrogen ion concentration change after the acid is added?
c. what happens to the ph of the solution in the beaker as the acid is added?

Explanation:

a.

Step1: Recall pH formula

pH is defined as \(pH = -\log_{10}[H^{+}]\). For pure water, \([H^{+}]=1\times10^{-7}\space mol/L\).

Step2: Calculate pH

Substitute \([H^{+}]\) into the formula: \(pH = -\log_{10}(1\times 10^{-7})\). Using the property \(\log_{10}(a\times10^{n})=n + \log_{10}(a)\), here \(a = 1\) and \(n=-7\), so \(pH=7\).

b.

Step1: Understand acid dissociation

Hydrochloric acid (\(HCl\)) is a strong acid. In water, \(HCl
ightarrow H^{+}+Cl^{-}\). When \(HCl\) is added to water, it increases the concentration of \(H^{+}\) ions.

c.

Step1: Relate \(H^{+}\) concentration and pH

Since \(pH = -\log_{10}[H^{+}]\), an increase in \([H^{+}]\) (from adding \(HCl\)) makes the \(\log_{10}[H^{+}]\) value more negative. But because of the negative sign in the pH formula, the pH of the solution decreases.

Answer:

a. The pH of pure water is \(7\).
b. The hydrogen - ion concentration increases after the acid is added.
c. The pH of the solution in the beaker decreases as the acid is added.