Q: A student titrates 0.02500 L of 0.100 M KHP with NaOH. If it takes 0.02450 L of NaOH to reach the endpoint, what is the molarity of the NaOH solution?

$$M_{\mathrm{NaOH}} = \frac{0.100 \times 0.02500}{0.02450} = 0.102\;\mathrm{M}$$

Q: If 10.00 mL of H$$_2SO$_4 is $$titrated with 13.75 mL of 0.100 M KOH, what is the molarity of the H$$_2SO$_4$$ solution? (Use the balanced equation: $$\mathrm{H_2SO_4 + 2KOH \rightarrow K_2SO_4 + 2H_2O})$$

$$M_{\mathrm{H_2SO_4}} = \frac{0.100 \times 0.01375}{2 \times 0.01000} = 0.0688\;\mathrm{M}$$

Question 1

Which of the following best describes the role of potassium hydrogen phthalate (KHP) in the standardization of sodium hydroxide solution?

Accepted Answer

KHP acts as a primary standard because it can be weighed accurately and reacts in a 1:1 molar ratio with NaOH.

Question 2

During the titration of acetic acid in vinegar with sodium hydroxide, which equation correctly represents the stoichiometric relationship at the equivalence point?

Accepted Answer

$$\mathrm{moles\;NaOH} = \mathrm{moles\;CH_3COOH}$$

Question 3

Why is phenolphthalein used as an indicator in the titration of acetic acid with sodium hydroxide?

Accepted Answer

Phenolphthalein changes color at the pH near the equivalence point of a weak acid-strong base titration, allowing visual detection of the endpoint.

Question 4

A student titrates 0.02500 L of 0.100 M KHP with NaOH. If it takes 0.02450 L of NaOH to reach the endpoint, what is the molarity of the NaOH solution?

Accepted Answer

$$M_{\mathrm{NaOH}} = \frac{0.100 	imes 0.02500}{0.02450} = 0.102\;\mathrm{M}$$

Question 5

Which of the following is a reason why sodium hydroxide is not used directly as a primary standard?

Accepted Answer

Sodium hydroxide is hygroscopic and absorbs moisture from the air, making accurate weighing difficult.

Question 6

In the titration of acetic acid with sodium hydroxide, what is the balanced chemical equation?

Accepted Answer

$$\mathrm{CH_3COOH\;(aq) + NaOH\;(aq) \rightarrow CH_3COONa\;(aq) + H_2O\;(l)}$$

Question 7

A student accidentally adds too much NaOH past the endpoint in the titration of vinegar. How will this affect the calculated mass percent of acetic acid in the vinegar?

Accepted Answer

The calculated mass percent will be too high because excess NaOH will be interpreted as reacting with more acetic acid than is actually present.

Question 8

Which of the following best explains why the end point of a titration is not exactly the same as the equivalence point?

Accepted Answer

The end point is detected by a color change of the indicator, which occurs slightly after the equivalence point due to the indicator's properties.

Question 9

If 10.00 mL of H$$_2SO$_4 is $$titrated with 13.75 mL of 0.100 M KOH, what is the molarity of the H$$_2SO$_4$$ solution? (Use the balanced equation: $$\mathrm{H_2SO_4 + 2KOH \rightarrow K_2SO_4 + 2H_2O})$$

Accepted Answer

$$M_{\mathrm{H_2SO_4}} = \frac{0.100 	imes 0.01375}{2 	imes 0.01000} = 0.0688\;\mathrm{M}$$

Question 10

Which of the following steps is essential to ensure the accuracy of a volumetric flask when preparing a primary standard solution?

Accepted Answer

Avoid crossing the calibrated mark when adding solvent to the flask.

Question 11

A student prepares 50.0 mL of approximately 0.10 M NaOH from a 1.0 M stock solution. What volume of the 1.0 M NaOH should be used?

Accepted Answer

$$V_1$$ = \frac{$$M_2$$ $$V_2$$}{$$M_1$$} = \frac{0.10 	imes 50.0}{1.0} = 5.0\;\mathrm{mL}$$

Question 12

Which of the following is a correct safety practice when handling sodium hydroxide solution in the laboratory?

Accepted Answer

Wear appropriate personal protective equipment and store the solution in secondary containment as directed.

Question 13

In the titration of KHP with NaOH, which of the following is the correct balanced chemical equation?

Accepted Answer

$$\mathrm{C_8H_5O_4K + NaOH \rightarrow C_8H_4O_4KNa + H_2O}$$

Question 14

A student titrates 0.100 g of acetic acid ($$\mathrm{CH_3COOH}$$, molar mass = 60.05 g/mol) with 0.100 M NaOH. How many mL of NaOH are required to reach the equivalence point?

Accepted Answer

$$\mathrm{moles\;CH_3COOH} = \frac{0.100}{60.05} = 0.001665\;\mathrm{mol}$$; $$V_{\mathrm{NaOH}} = \frac{0.001665}{0.100} = 0.01665\;\mathrm{L} = 16.65\;\mathrm{mL}$$

Question 15

Which of the following best explains why it is important to stop the titration at the first appearance of a permanent pale pink color when using phenolphthalein?

Accepted Answer

To ensure the titration is stopped as close as possible to the equivalence point, minimizing excess base addition.

Question 16

A student prepares a KHP solution by dissolving 0.510 g of KHP (molar mass = 204.22 g/mol) in enough water to make 25.00 mL of solution. What is the molarity of the KHP solution?

Accepted Answer

$$\mathrm{moles\;KHP} = \frac{0.510}{204.22} = 0.002498\;\mathrm{mol}$$; $$M = \frac{0.002498}{0.02500} = 0.100\;\mathrm{M}$$

Question 17

In a real-world scenario, why is it important to determine the mass percent of acetic acid in commercial vinegar?

Accepted Answer

To ensure the product meets food safety and quality standards for consumer use.

Question 18

Which of the following calculations is used to determine the mass percent of acetic acid in a vinegar sample?

Accepted Answer

$$\mathrm{Mass\;percent} = \frac{\mathrm{mass\;of\;CH_3COOH}}{\mathrm{mass\;of\;vinegar\;sample}} 	imes 100\%$$

Vinegar Titration: Determining Acetic Acid Content via Acid-Base Titration

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