Understanding Solvation and Dissociation

Develop a model to illustrate the process of dissolving table salt (NaCl) in water. Explain the roles of solvation and dissociation in this process.

• Solvation involves the breaking of ionic bonds in NaCl, while dissociation involves the formation of new covalent bonds with water molecules.

• Solvation involves water molecules surrounding Na+ and Cl- ions, while dissociation involves the separation of NaCl into Na+ and Cl- ions.

• Solvation involves the evaporation of water, while dissociation involves the condensation of NaCl.

• Solvation and dissociation both involve the formation of a new compound between NaCl and water.

Answer explanation

The correct choice explains that solvation is the process where water molecules surround the separated Na+ and Cl- ions, while dissociation refers to the breaking apart of NaCl into these ions, highlighting the key steps in dissolving salt.

Plan an investigation to determine how temperature affects the rate at which sugar dissolves in water. What steps would you include in your plan?

• Measure the mass of sugar before and after dissolving at different temperatures.

• Use a thermometer to measure the temperature of the water and a stopwatch to time how long it takes for the sugar to dissolve completely at each temperature.

• Change the amount of water used in each trial to see how it affects the dissolving rate.

• Use different types of sugar to see which dissolves fastest.

Answer explanation

The correct choice involves using a thermometer to measure water temperature and a stopwatch to time the sugar's dissolution. This directly assesses how temperature influences the rate of dissolving, which is the investigation's focus.

Calculate the molarity of a solution made by dissolving 5 moles of solute in 2 liters of solution.

• 2.5 M

• 5 M

• 10 M

• 2 M

Answer explanation

Molarity (M) is calculated as moles of solute divided by liters of solution. Here, 5 moles / 2 liters = 2.5 M. Therefore, the correct answer is 2.5 M.

Communicate the steps required to prepare a 1 M solution of NaCl, including how to properly label the solution.

• Dissolve 58.44 g of NaCl in 1 L of water, label the solution as "1 M NaCl Solution."

• Dissolve 100 g of NaCl in 1 L of water, label the solution as "1 M NaCl Solution."

• Dissolve 58.44 g of NaCl in 500 mL of water, label the solution as "1 M NaCl Solution."

• Dissolve 100 g of NaCl in 500 mL of water, label the solution as "1 M NaCl Solution."

Answer explanation

To prepare a 1 M NaCl solution, dissolve 58.44 g of NaCl in 1 L of water. This is the correct molar mass for NaCl, ensuring the solution is accurately labeled as "1 M NaCl Solution."

Develop a model to explain how adding salt to water affects its boiling point.

• Adding salt decreases the boiling point because it increases the vapor pressure.

• Adding salt increases the boiling point because it decreases the vapor pressure.

• Adding salt has no effect on the boiling point.

• Adding salt increases the boiling point because it increases the vapor pressure.

Answer explanation

Adding salt to water increases the boiling point due to a phenomenon called boiling point elevation. The presence of salt decreases the vapor pressure of the solution, requiring a higher temperature to reach the boiling point.

Explain how you would use evidence to determine whether a solute dissociates or merely dissolves in a solvent.

• Measure the change in temperature of the solution.

• Observe the color change of the solution.

• Conduct an electrical conductivity test to see if ions are present in the solution.

• Measure the pH of the solution.

Answer explanation

Conducting an electrical conductivity test is the best way to determine if a solute dissociates into ions in solution. If ions are present, it indicates dissociation; if not, the solute merely dissolves.

Design an experiment to evaluate how stirring affects the rate at which a solute dissolves in water.

• Use a thermometer to measure the temperature change during stirring.

• Use a balance to measure the mass of solute before and after stirring.

• Use a stopwatch to time how long it takes for the solute to dissolve with and without stirring.

• Use a pH meter to measure the pH change during stirring.

Answer explanation

Using a stopwatch to time how long it takes for the solute to dissolve with and without stirring directly measures the effect of stirring on the dissolution rate, making it the most relevant choice for this experiment.

Calculate the percent by mass of a solution containing 10 g of solute in 90 g of solvent.

• 10%

• 11.11%

• 9%

• 12%

Answer explanation

To find the percent by mass, use the formula: (mass of solute / total mass) x 100. Here, total mass = 10 g (solute) + 90 g (solvent) = 100 g. Thus, (10 g / 100 g) x 100 = 10%. The correct answer is 11.11%.

Describe the process of preparing a 0.5 M solution of KCl and how you would label it.

• Dissolve 37.27 g of KCl in 1 L of water, label the solution as "0.5 M KCl Solution."

• Dissolve 74.55 g of KCl in 1 L of water, label the solution as "0.5 M KCl Solution."

• Dissolve 37.27 g of KCl in 500 mL of water, label the solution as "0.5 M KCl Solution."

• Dissolve 74.55 g of KCl in 500 mL of water, label the solution as "0.5 M KCl Solution."

Answer explanation

To prepare a 0.5 M KCl solution, you need to dissolve 37.27 g of KCl in 1 L of water. This concentration means that in 1 L, there are 0.5 moles of KCl, which is correctly achieved with this amount. Label it as '0.5 M KCl Solution.'

Develop a model to explain how adding antifreeze to water affects its freezing point.

• Adding antifreeze raises the freezing point because it increases the vapor pressure.

• Adding antifreeze lowers the freezing point because it disrupts the formation of ice crystals.

• Adding antifreeze has no effect on the freezing point.

• Adding antifreeze raises the freezing point because it decreases the vapor pressure.

Answer explanation

Adding antifreeze lowers the freezing point because it disrupts the formation of ice crystals, preventing water molecules from organizing into a solid structure, thus requiring a lower temperature to freeze.