Question 1

Which of the following statements best explains why water is used as the first solvent in a solubility test for organic compounds?

Accepted Answer

Water is a polar solvent and can help distinguish between polar and nonpolar compounds based on their solubility.

Question 2

A student tests an unknown organic compound for solubility in 5% NaOH and observes that it dissolves completely. Which functional group is most likely present in the compound?

Accepted Answer

A carboxylic acid group, which reacts with NaOH to form a soluble carboxylate salt.

Question 3

Which of the following equations correctly represents the reaction of benzoic acid with sodium hydroxide during a solubility test?

Accepted Answer

$$\mathrm{C_6H_5COOH} + \mathrm{NaOH} \rightarrow \mathrm{C_6H_5COONa} + \mathrm{H_2O}$$

Question 4

During a solubility test, a compound is found to be insoluble in water but soluble in 5% HCl. What does this suggest about the compound's functional group?

Accepted Answer

The compound is likely a basic amine, which forms a soluble ammonium salt with HCl.

Question 5

Which of the following is a correct observation indicating that a compound is soluble in water during a solubility test?

Accepted Answer

Formation of a homogeneous solution with no visible solid.

Question 6

A student tests phenol for solubility in 5% NaOH and observes that it dissolves. Which reaction best explains this observation?

Accepted Answer

$$\mathrm{C_6H_5OH} + \mathrm{NaOH} \rightarrow \mathrm{C_6H_5ONa} + \mathrm{H_2O}$$

Question 7

Which of the following compounds would you expect to be soluble in 5% NaHCO$$_3$$ but not in water?

Accepted Answer

Benzoic acid, because it is a stronger acid than phenol and reacts with NaHCO$$_3 to $$form a soluble salt.

Question 8

In the schematic diagram for solubility tests, which step is performed immediately after a compound is found to be insoluble in water?

Accepted Answer

Test solubility in 5% NaOH.

Question 9

Which of the following best describes the role of intermolecular forces in the solubility of organic compounds?

Accepted Answer

Solubility depends on the balance of intermolecular forces between solute and solvent molecules.

Question 10

A student observes that an unknown sample is insoluble in water, insoluble in 5% NaOH, but soluble in 5% HCl. Which functional group is most likely present?

Accepted Answer

A basic amine group.

Question 11

Which of the following compounds would NOT be expected to dissolve in 5% NaOH?

Accepted Answer

Cyclohexane, because it is a nonpolar hydrocarbon.

Question 12

Why is it important to use only a small amount of sample and solvent in solubility tests?

Accepted Answer

To minimize waste and reduce exposure to hazardous chemicals.

Question 13

Which of the following observations would indicate that a compound is insoluble in water?

Accepted Answer

Solid particles remain visible after shaking.

Question 14

A student tests an unknown compound and finds it is soluble in water and 5% NaOH, but insoluble in 5% HCl. Which functional group is most likely present?

Accepted Answer

Carboxylic acid group.

Question 15

Which of the following is a correct safety precaution when handling concentrated acids and bases during solubility tests?

Accepted Answer

Wear gloves and eye protection to prevent skin and eye contact.

Question 16

Which of the following best explains why benzoic acid is soluble in 5% NaOH but not in water?

Accepted Answer

Benzoic acid is a weak acid and forms a soluble salt with NaOH, but remains mostly undissociated in water.

Question 17

Which of the following is the correct order of solvents used in the solubility test for organic compounds, according to the schematic diagram?

Accepted Answer

Water, 5% NaOH, 5% NaHCO$$_3$$, 5% HCl

Question 18

Which of the following functional groups is most likely to be present in a compound that is soluble in 5% NaOH but insoluble in 5% NaHCO$$_3$$?

Accepted Answer

Phenol group, because it is a weak acid and reacts with NaOH but not with NaHCO$$_3.$$

Question 19

A student tests an unknown sample and finds it is insoluble in water, 5% NaOH, and 5% HCl. What is the most likely reason for this observation?

Accepted Answer

The compound is a nonpolar hydrocarbon, such as cyclohexane.

EXP. 6: Solubility Test for Organic Compounds

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