Q: Which equation is used to calculate pH?

$$\text{pH} = -\log_{10}[H^+]$$

Question 1

Which of the following best describes the main factor that determines the physical and chemical properties of a molecule?

Accepted Answer

The molecular structure, including the types and arrangement of atoms

Question 2

What is the definition of an extraction in chemistry?

Accepted Answer

A process to transfer a substance from one phase to another, usually to separate it from a mixture

Question 3

Which formula is used to calculate the partition coefficient $$K$$ for a solute distributed between two immiscible solvents?

Accepted Answer

$$K = \frac{[C]_{organic}}{[C]_{water}}$$

Question 4

Which of the following best describes the extraction yield (extractierendement)?

Accepted Answer

The ratio of the amount extracted to the initial amount, expressed as a percentage

Question 5

A chemist wants to maximize the extraction yield. Which condition should the partition coefficient $$K$$ satisfy?

Accepted Answer

$$K$$ should be much greater than 1

Question 6

Which formula would you use to calculate the remaining amount of solute after $$n$$ extractions?

Accepted Answer

$$q_n = q_0$ \left( \frac{V_{aq}}{K V_{org} + V_{aq}} \right)^n$$

Question 7

How does pH influence the efficiency of an extraction involving a weak acid?

Accepted Answer

A lower pH increases the amount of neutral acid in the organic phase

Question 8

Which equation is used to calculate pH?

Accepted Answer

$$	ext{pH} = -\log_{10}[H^+]$$

Question 9

What is the main difference between the distribution coefficient $$D$$ and the partition coefficient $$K$$?

Accepted Answer

$$D$$ considers all forms of the solute, while $$K$$ considers only the neutral form

Question 10

Which formula is used to calculate the distribution coefficient $$D$$ when both neutral and ionized forms are present?

Accepted Answer

$$D = K \frac{[HA]}{[HA] + [A^-]}$$

Question 11

A student needs to choose a pH for efficient extraction of a weak base into an organic solvent. What should they do?

Accepted Answer

Choose a pH above the pKa of the base

Question 12

Which of the following best describes chromatography?

Accepted Answer

A technique to separate compounds based on their distribution between a stationary and a mobile phase

Question 13

What is the main difference between chromatography and liquid-liquid extraction?

Accepted Answer

Chromatography uses a stationary and a mobile phase, while liquid-liquid extraction uses two immiscible liquid phases

Question 14

If a compound has a partition coefficient $$K = 10$$ between chloroform and water, and you extract 100 mg of the compound from 100 mL water with 100 mL chloroform, how much remains in the water after one extraction?

Accepted Answer

$$q = 100 	imes \frac{1}{K+1} = 100 	imes \frac{1}{11} \approx 9.1 mg$$

Question 15

Which of the following is a requirement for a high extraction yield in a liquid-liquid extraction?

Accepted Answer

The solute should be more soluble in the extracting solvent than in the original solvent

Question 16

Which of the following best describes the effect of increasing the number of extractions with smaller volumes of solvent?

Accepted Answer

It increases the total amount extracted compared to a single extraction with the same total volume

Week 1: Molecular Structure, Extraction, and Separation Techniques – Study Guidance

Study Guide - Practice Questions

Study Guide - Flashcards