How can you find the concentration of hydroxide ions in a solution?

The concentration of hydroxide ions in a solution can be determined using the relationship between the concentrations of hydrogen ions and hydroxide ions, expressed by the ion product of water, Kw. The equation [OH^-] = Kw / [H^+] is derived from the fact that Kw is the product of the concentrations of hydrogen ions and hydroxide ions in water at a given temperature (25°C, Kw = 1.0 × 10^-14).

When you have the concentration of hydrogen ions in a solution, you can rearrange the equation to find the concentration of hydroxide ions. This is particularly useful because it takes advantage of the known value of Kw, allowing you to calculate [OH^-] if you have measured or determined the [H^+].

For example, if the concentration of hydrogen ions is known to be 1.0 × 10^-7 M, substituting this value into the equation would yield [OH^-] = 1.0 × 10^-14 / 1.0 × 10^-7, resulting in [OH^-] = 1.0 × 10^-7 M as well.

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