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Multiple Choice
What is the pH of a solution made by mixing 25.00 mL of 0.100 M HCl with 40.00 mL of 0.100 M KOH? Assume that the volumes of the solutions are additive.
A
pH = 12.00
B
pH = 5.00
C
pH = 2.00
D
pH = 7.00
Verified step by step guidance
1
First, determine the moles of HCl and KOH in the solution. Use the formula \( \text{moles} = \text{concentration} \times \text{volume} \). For HCl: \( \text{moles of HCl} = 0.100 \, \text{M} \times 25.00 \, \text{mL} \times \frac{1 \, \text{L}}{1000 \, \text{mL}} \). For KOH: \( \text{moles of KOH} = 0.100 \, \text{M} \times 40.00 \, \text{mL} \times \frac{1 \, \text{L}}{1000 \, \text{mL}} \).
Next, identify the reaction between HCl and KOH. The balanced chemical equation is \( \text{HCl} + \text{KOH} \rightarrow \text{KCl} + \text{H}_2\text{O} \). This is a neutralization reaction where HCl and KOH react in a 1:1 molar ratio.
Calculate the moles of HCl and KOH that react. Since they react in a 1:1 ratio, the limiting reactant will be the one with fewer moles. Compare the moles of HCl and KOH calculated in the first step to determine the limiting reactant.
Determine the moles of excess KOH after the reaction. Subtract the moles of HCl from the moles of KOH to find the moles of KOH remaining after the reaction.
Calculate the concentration of the excess KOH in the final solution. Use the formula \( \text{concentration} = \frac{\text{moles of excess KOH}}{\text{total volume of solution in liters}} \). The total volume is the sum of the initial volumes of HCl and KOH solutions. Finally, use the concentration of KOH to find the pOH and then the pH using the relation \( \text{pH} + \text{pOH} = 14 \).