Question

What is the molarity of a solution made by dissolving \( 2.5 \, \text{g} \) of potassium chloride (\( \text{KCl} \)) in \( 500 \, \text{mL} \) of water? (Molar mass of \( \text{KCl} = 74.5 \, \text{g/mol} \))

• A. \( 0.10 \, \text{M} \)
• B. \( 0.25 \, \text{M} \)
• C. \( 0.50 \, \text{M} \)
• D. \( 1.00 \, \text{M} \)

Hint:

Molarity is calculated by dividing the moles of solute by the volume of solution in liters. Always convert the mass of the solute to moles using its molar mass and ensure the volume is in liters.

Answer 1

The Correct Option is A

To calculate the molarity of the solution, we first need to calculate the number of moles of \( \text{KCl} \). \[ \text{moles of KCl} = \frac{\text{mass of KCl}}{\text{molar mass of KCl}} = \frac{2.5 \, \text{g}}{74.5 \, \text{g/mol}} \approx 0.0336 \, \text{mol} \] Now, convert the volume of the solution from milliliters to liters: \[ \text{volume of solution} = 500 \, \text{mL} = 0.500 \, \text{L} \] Now, calculate the molarity: \[ M = \frac{\text{moles of KCl}}{\text{volume of solution in liters}} = \frac{0.0336 \, \text{mol}}{0.500 \, \text{L}} = 0.0672 \, \text{M} \] Thus, the molarity of the solution is \( 0.10 \, \text{M} \).