Quiz: Aqueous Solutions and Concentrations — 9 questions

1. Which description correctly defines a solution?

A. A mixture in which the solvent remains undissolved beneath the solute

B. A pure substance made from a single chemical species

C. A heterogeneous mixture formed when several substances remain visibly separate

D. A homogeneous mixture formed when one or more solutes dissolve in a solvent

Answer: (D)

Explanation

A solution is uniform throughout because one or more solutes dissolve in a solvent. A heterogeneous mixture differs because its composition is not uniform throughout.

2. What does mass concentration measure?

A. The volume of dissolved solute per kilogram of solution

B. The mass of solvent required to dissolve one litre of solute

C. The mass of dissolved solute per litre of solution

D. The total mass of solution per litre of solvent

Answer: (C)

Explanation

Mass concentration measures how much solute mass is dissolved in each litre of solution. It is different from density, which concerns the total mass of the solution.

3. A solution contains $6.0\,\text{g}$ of dissolved solute in $0.50\,\text{L}$ of solution. What is its mass concentration?

A. $0.083\,\text{g·L}^{-1}$

B. $6.5\,\text{g·L}^{-1}$

C. $3.0\,\text{g·L}^{-1}$

D. $12\,\text{g·L}^{-1}$

Answer: (D)

Explanation

Using $C_m=\frac{m}{V}$ gives $C_m=\frac{6.0\,\text{g}}{0.50\,\text{L}}=12\,\text{g·L}^{-1}$. Multiplying the mass by the volume would not apply the mass-concentration relationship.

4. In a solution containing a small amount of dissolved salt and a large amount of water, which roles do the two substances have?

A. Both salt and water are solvents because the mixture is homogeneous

B. Salt is the solute, and water is the solvent

C. Both salt and water are solutes because they form a mixture

D. Salt is the solvent, and water is the solute

Answer: (B)

Explanation

The solute is the dissolved species and is often the minor component, while the solvent is the major species. Water therefore acts as the solvent and dissolved salt acts as the solute.

5. What is a solution in chemistry?

A. A mixture where the components are visibly distinct and not uniformly distributed.

B. A pure substance made up of only one type of molecule.

C. A heterogeneous mixture with varying composition throughout.

D. A homogeneous mixture obtained by dissolving one or more solutes in a solvent.

Answer: (D)

Explanation

A solution is defined as a homogeneous mixture obtained by dissolving one or more solutes in a solvent. The other options describe different types of mixtures or pure substances, which are not solutions.

6. What is the primary difference between a solute and a solvent in a solution?

A. The solute is always water, while the solvent can be any liquid.

B. The solute is the liquid, and the solvent is the solid in a solution.

C. The solute is the component present in the largest amount, and the solvent is the component in the smallest amount.

D. The solute is the dissolved chemical species and is often minor or unique, whereas the solvent is the major component.

Answer: (D)

Explanation

The solute is the chemical species that dissolves and is usually present in minor amounts, while the solvent is the major component that dissolves the solute. The other options incorrectly assign the roles or specify the wrong components.

7. What is the main purpose of measuring mass concentration in a solution?

A. To determine the amount of solute dissolved per unit volume of solution.

B. To find the total mass of the solution.

C. To measure the density of the solution.

D. To calculate the solubility limit of a solute.

Answer: (A)

Explanation

The primary purpose of measuring mass concentration is to determine how much solute is dissolved per liter of solution, which helps assess solution composition. Measuring density, for example, relates to mass density, not mass concentration, and does not directly indicate solute amount.

8. How does mass concentration differ from mass density in the context of solutions?

A. Mass concentration measures the mass of the solution per unit volume, while mass density measures the mass of the solute per unit volume.

B. Mass concentration is the total mass of the solution divided by its volume, whereas mass density is the mass of the solute per volume.

C. Mass concentration measures the mass of solute per volume, while mass density measures the total mass of the solution per volume.

D. Mass concentration and mass density are identical quantities expressed in different units.

Answer: (C)

Explanation

Mass concentration specifically refers to the mass of dissolved solute per volume of solution, calculated as $C_m=\frac{m_{\mathrm{solute}}}{V}$, while mass density measures the total mass of the entire solution per volume, given by $\rho=\frac{m_{\mathrm{solution}}}{V}$. The key difference is that mass density includes the mass of both solute and solvent, whereas mass concentration pertains only to the solute.

9. Who is credited with proposing the concept of concentration by calibration in chemical solutions?

A. The concept was proposed by Wilhelm Ostwald.

B. The concept was proposed by Robert Boyle.

C. The concept was proposed by Marie Curie.

D. The concept was proposed by Antoine Lavoisier.

Answer: (A)

Explanation

Wilhelm Ostwald is credited with proposing the method of concentration by calibration, which involves comparing an unknown solution with standard solutions to determine its concentration. The other scientists made significant contributions to chemistry but are not credited with this specific concept.