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pH & Strong Acids

01pH & Strong Acids

pH and hydrogen ions

This section covers the pH scale and conversion between pH and hydrogen ion concentration.

Calculating pH

The pH scale is a logarithmic way of expressing the concentration of hydrogen ions in an aqueous solution.

pH=−log⁡10[HX+]\mathrm{pH}=-\log_{10}[\ce{H+}]

Here, [HX+][\ce{H+}] is the hydrogen ion concentration in mol dm−3\mathrm{mol\,dm^{-3}}.

Finding hydrogen ion concentration

The pH equation can be reversed to calculate [HX+][\ce{H+}] when the pH is known:

[HX+]=10−pH[\ce{H+}]=10^{-\mathrm{pH}}

Worked example: Find the concentration of hydrochloric acid when its pH is 1.35.

For hydrochloric acid, use:

[HX+]=10−1.35[\ce{H+}]=10^{-1.35}

[HX+]=4.47×10−2 mol dm−3[\ce{H+}]=4.47\times10^{-2}\ \mathrm{mol\,dm^{-3}}

Therefore the concentration is approximately 0.045 mol dm−30.045\ \mathrm{mol\,dm^{-3}}.

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