Question 1

During a typical liquid-liquid extraction, which of the following statements best describes the separation process?

Accepted Answer

A component is selectively transferred from one liquid phase to another based on its solubility.

Question 2

In an acid-base extraction, why is it generally preferable to add a weak base before a strong base?

Accepted Answer

To selectively deprotonate the strongest acid first, allowing for stepwise separation.

Question 3

Which of the following compounds would be extracted into the aqueous layer upon addition of NaOH (a strong base) to a mixture containing acetic acid, phenol, and propane?

Accepted Answer

Acetic acid

Question 4

A student is performing an extraction and wants to increase the solubility of a compound in the aqueous layer. Which of the following strategies would be most effective?

Accepted Answer

Convert the compound to its ionic form.

Question 5

Which of the following best explains why the non-ionic form of a compound is more soluble in the organic layer during extraction?

Accepted Answer

Non-ionic compounds are less polar and thus dissolve better in organic solvents.

Question 6

A mixture contains phenol ($$pK_a = 9.98) $$and acetic acid ($$pK_a = 4.76). $$Which base would you add first to selectively extract acetic acid into the aqueous layer?

Accepted Answer

$$\mathrm{$$NaHCO_3$$}$$

Question 7

If you add $$\mathrm{$$NaHCO_3$$} to a $$mixture containing acetic acid and phenol, what will happen?

Accepted Answer

Only acetic acid will be deprotonated and move to the aqueous layer.

Question 8

During an extraction, a student adds $$\mathrm{HCl} to a $$mixture containing aniline (a weak base) and phenol. What is the expected outcome?

Accepted Answer

Aniline will form a water-soluble salt and move to the aqueous layer.

Question 9

Which of the following best describes the role of pH in liquid-liquid extraction?

Accepted Answer

pH affects the ionization state of compounds, altering their solubility in aqueous or organic layers.

Question 10

A mixture contains benzoic acid ($$pK_a = 4.2) $$and naphthalene (non-acidic). Which reagent would you use to selectively extract benzoic acid into the aqueous layer?

Accepted Answer

$$\mathrm{NaOH}$$

Question 11

Which of the following statements about the use of a separatory funnel in extraction is correct?

Accepted Answer

The less dense layer forms the top layer, which is often the organic layer.

Question 12

A student is trying to extract a weak acid from a mixture. Which of the following steps should they take to maximize extraction into the aqueous layer?

Accepted Answer

Add a base to deprotonate the acid, forming a water-soluble salt.

Question 13

Which of the following best explains why a component may be selectively removed from a mixture by precipitation in a new solvent?

Accepted Answer

The component is less soluble in the new solvent, causing it to precipitate.

Question 14

If a compound is more soluble in the organic layer when non-ionic, what change would increase its solubility in the aqueous layer?

Accepted Answer

Convert it to its ionic form by adjusting the pH.

Question 15

A mixture contains a weak acid and a neutral compound. After adding a base, which layer will the deprotonated acid be found in?

Accepted Answer

Aqueous layer

Question 16

Which of the following is the most commonly used form of extraction in laboratory settings?

Accepted Answer

Liquid-liquid extraction

Question 17

A student is separating a mixture of benzoic acid, aniline, and naphthalene. Which sequence of reagents would allow for the stepwise extraction of each component?

Accepted Answer

Add $$\mathrm{$$NaHCO_3$$}$$, then $$\mathrm{HCl}$$, then $$\mathrm{NaOH}$$

Question 18

Which of the following best describes the effect of adding a strong acid to a solution containing a weak base during extraction?

Accepted Answer

The weak base is protonated, forming a water-soluble salt.

Question 19

In a real-world scenario, why is it important to know the $$pK_a$$ values of compounds when performing an acid-base extraction?

Accepted Answer

To determine the order in which compounds will be extracted based on their acidity.

Extraction Techniques and Acid-Base Extraction in GOB Chemistry

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