Solutions & Mixtures (College Board AP® Chemistry): Exam Questions

A student prepares a 250.0 mL solution of 0.250 M NaCl by diluting a more concentrated solution.

Describe what molarity represents and explain how it is used in solution calculations.

Calculate the volume of 1.00 M NaCl stock solution required to prepare 250.0 mL of the 0.250 M solution.

Describe how to accurately prepare 250.0 mL of 0.250 M NaCl solution in a laboratory.

Explain what happens to the molarity and total number of moles of solute when a solution is diluted.

A forensic scientist is analyzing a mixture of dyes using paper chromatography to determine if a suspect’s pen matches ink found at a crime scene.

Explain why chromatography is effective for separating the components of a solution.

Describe the function of the mobile phase and stationary phase in paper chromatography.

The scientist measures the R_f values of two dyes in an ink sample, recording 0.35 and 0.72.

i) Which dye has a stronger interaction with the stationary phase? Justify your answer.

ii) Predict how changing the mobile phase to a more polar solvent would affect the R_f values of both dyes.

A student is investigating the miscibility of three liquids: ethanol, hexane, and water.

Predict whether ethanol and hexane are miscible in each other, and justify your answer based on intermolecular forces.

Explain how hydrogen bonding in water influences the solubility of other substances in water.

A student adds acetone to both water and hexane.

Predict which liquid acetone will mix better with, and justify your answer in terms of relative intermolecular force strengths.

Seawater contains dissolved salts like NaCl, MgCl₂, and CaCl₂. These ions affect properties such as conductivity and salinity, which are important in environmental and marine chemistry.

Explain, in terms of interactions at the molecular level, why ionic compounds such as NaCl, MgCl₂, and CaCl₂ dissolve readily in water.

Explain how these interactions allow seawater to conduct electricity.

A seawater sample contains the following concentrations:

• 0.550 M NaCl

• 0.250 M MgCl₂

• 0.100 M CaCl₂

Calculate the total concentration of ions (all dissolved particles) in the solution.

Explain why a 1.0 M solution of MgCl₂ conducts electricity better than a 1.0 M solution of NaCl.

The diagram below shows a simple distillation setup used to separate pure water from seawater.

i) Label the component where salt remains, and the component where pure water collects.

ii) Explain why this method successfully separates water from dissolved salts.

A student starts with 100.0 mL of seawater containing dissolved salts from part (c).

i) Assuming this residue consists of a mixture of NaCl, MgCl₂, and CaCl₂ in the same mole ratio as in part (c), calculate the percentage by mass of NaCl in the total dissolved salts.

ii) After distillation of the 100.0 mL sample, 4.92 g of solid residue is recovered. Assuming this residue retains the same composition as in part (i), calculate the mass of NaCl present in the solid.