A student performed three KHP titrations in Part 1 in order to standardize their NaOH solution. They reported the following measurements:

Question

Determination #1 Determination #2 Determination #3
Mass of KHP + Vial 14.0862 g 14.5621 g 14.3998 g
Mass of 'Empty' Vial 13.2492 g 13.7695 g 13.6887 g
Final Burette Reading 45.10 mL 38.53 mL 37.17 mL
Initial Burette Reading 5.08 mL 0.52 mL 3.19 mL
How many moles of NaOH did they use in their first titration (ie. their first determination)? Report your answer to the correct number of significant figures and only report the numerical value (no units).

Answer 1

To calculate the moles of NaOH used in the first titration, we need to follow these steps:

1. Calculate the mass of KHP used: \[ \text{Mass of KHP} = \text{Mass of KHP + Vial} - \text{Mass of 'Empty' Vial} \] For Determination #1: \[ \text{Mass of KHP} = 14.0862 , \text{g} - 13.2492 , \text{g} = 0.8370 , \text{g} \]

2. Calculate the number of moles of KHP: KHP (potassium hydrogen phthalate) has a molar mass of approximately 204.22 g/mol. \[ \text{Moles of KHP} = \frac{\text{mass of KHP}}{\text{molar mass of KHP}} = \frac{0.8370 , \text{g}}{204.22 , \text{g/mol}} \] \[ \text{Moles of KHP} \approx 0.004103 , \text{mol} \]

3. Determine the moles of NaOH used: The reaction between KHP and NaOH is 1:1. Therefore, the moles of NaOH used is equal to the moles of KHP. \[ \text{Moles of NaOH} = \text{Moles of KHP} \approx 0.004103 , \text{mol} \]

4. Report the answer to the correct number of significant figures: The mass of KHP is reported to four significant figures, so we should also report the moles of NaOH to four significant figures.

Thus, the final answer is:

0.004103