The probe of the pH meter shown here is sitting in a beaker that contains a clear liquid. You are told the liquid is pure water, a solution of HCl(aq), or a solution of KOH(aq). (b) If the liquid is one of the solutions, what is its molarity?

Verified step by step guidance

1. Identify the pH value from the pH meter, which is 12.85.
2. Determine the nature of the solution based on the pH value. Since the pH is greater than 7, the solution is basic.
3. Recognize that KOH (potassium hydroxide) is a strong base and is likely the solution in the beaker.
4. Use the pH value to find the pOH value using the relationship: pH + pOH = 14.
5. Calculate the molarity of the KOH solution by finding the concentration of OH- ions using the formula: [OH-] = 10^(-pOH).

Key Concepts

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is neutral, below 7 indicates acidity, and above 7 indicates basicity. In this case, a pH of 12.85 suggests a strongly basic solution, which is consistent with a KOH solution.

Molarity

Molarity (M) is a measure of concentration defined as the number of moles of solute per liter of solution. It is crucial for determining the strength of an acid or base in a solution. To find the molarity of HCl or KOH, one can use the pH value to calculate the concentration of hydroxide ions (OH-) or hydrogen ions (H+), respectively.

Strong Acids and Bases

Strong acids, like HCl, and strong bases, like KOH, completely dissociate in water. This means that the concentration of the acid or base in solution directly corresponds to the concentration of H+ or OH- ions. Understanding this dissociation is essential for calculating molarity from pH, as it allows for straightforward conversions between pH and ion concentration.