Video: Applying Knowledge of Bases, H⁺ Ion Concentration and the pH Scale

For statements I and II, state for each if they are true or false. I) A 1 M solution of potassium hydroxide has a low pH. II) Solutions with a low H⁺ concentration have a low pH. If both are true, state if two is a correct explanation for I.

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Video Transcript

For statements one and two, state for each if they are true or false. I) A one molar solution of potassium hydroxide has a low pH. II) Solutions with a low H⁺ concentration have a low pH. If both are true, state if two is a correct explanation for one.

A one molar solution of potassium hydroxide has one mole of potassium hydroxide per liter of solution. When potassium hydroxide dissolves in water, it associates to form potassium plus ions and OH⁻ ions. pH is a measure of the acidity of a solution. A value of seven indicates a solution which is neutral, with higher values indicating a basic solution and lower values indicating an acidic solution. pH is calculated by taking the negative log of the concentration of hydronium ions, H⁺. Water will naturally react with itself to a small degree, forming H₃O⁺ ions and OH⁻ ions. The equilibrium constant for this process is relatively small at 25 degrees Celsius equal to one times 10 to the minus 14.

When potassium hydroxide is introduced to water, the extra hydroxide ions react with the hydronium ions, shifting the equilibrium to the left. H₃O⁺ and H⁺ refer to the same ion in solution. H⁺ is just a shorthand. Since pH is the negative log of the hydrogen ion concentration, the lower the hydrogen ion concentration, the higher the pH. And the more basic the solution is. So statement one is actually false. A one molar solution of potassium hydroxide would have a high hydroxide concentration, a low hydronium concentration, and a high pH. Statement two is a general statement about solutions with a low hydronium ion concentration, having a low pH. This is the exact opposite of what we’ve just demonstrated for the potassium hydroxide solution. A low H⁺ concentration will lead to a high pH, not a low one. So statement two is also false. Since both statements are false, we don’t have to address the next part of the question.

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