Lesson 23: Properties of Solutions

Read the scenario. A scientist dissolves 5 g of potassium chloride (KCl) crystals in a bottle of water until the final volume is 100mL. Which answer choice shows the correct way to label the concentration of the potassium chloride solution described in the scenario?

5% (m/v) KCI

How are the terms solubility and saturated solution related?

A saturated solution is the result of a solute reaching the current limit of its solubility.

What is a supersaturated solution?

A supersaturated solution forms when the amount of solute dissolved into a particular solvent is more than the maximum amount of solute that normally dissolves in that solvent for a given temperature and pressure, which is also known as its solubility.

Examine the statements. Solution A has a total volume of 1000 mL and contains 100 mL of chlorine (Cl). Solution B has a total volume of 100 mL and contains 10 mL of chlorine (Cl). Solution C has a total volume of 2000 mL and contains 200 mL of chlorine (Cl). Solution D has a total volume of 500 mL and contains 50 mL of chlorine (Cl). Which solution has the highest concentration of chlorine, if any? Hint: Recall the definition of concentration and the formula for calculating volume percent.

All solutions have the same concentration: 10%. Concentration is the amount of a solute in a solution compared to the total solution. To find the volume percent of a solution, you should use the following equation: (Solute Volume / Solution Volume) x 100 Solution A has 100 mL of solute compared to 1000 mL of solution, and 100/1000 = 0.1 x 100 = 10%. Solution B has 10 mL of solute compared to 100 mL of solution, and 10/100 = 0.1 x 100 = 10%. Solution C has 200 mL of solute compared to 2000 mL of solution, and 200/2000 = 0.1 x 100 = 10%. Solution D has 50 mL of solute compared to 500 mL of solution, and 50/500 = 0.1 x 100 = 10%.

Between table salt and rock salt, which substance will dissolve faster in water? Explain your reasoning.

The salt from the salt shaker will dissolve faster because it contains many small crystals, which gives it a larger surface area (compared to its volume) than the rock salt.

What would the scientist have to do to make the solution saturated, if anything?

The scientist would need to add 160 g of salt to the solution.

What would the scientist have to do to make the solution supersaturated, if anything?

The scientist would need to heat the solution, add more than 160 g of salt to it, and then cool the solution back down to room temperature.

Between an opened and closed soda can, which soda most likely has the most dissolved carbon dioxide? Explain your reasoning.

The soda on the right has the most dissolved carbon dioxide because it is unopened and has more pressure applied to it.

Examine the statement before answering the next three questions. The solubility of table salt (NaCl) at room temperature is 360 g/L. A scientist has a room-temperature solution that contains 1 liter of water and 200 g of salt. What would the scientist have to do to make the solution unsaturated, if anything?

The solution is already unsaturated; the scientist would not need to change anything.

Between using an electric meter and a whisk, In which of the mixtures would sugar dissolve the fastest? Explain your reasoning.

The sugar would dissolve the fastest in the mixture on the left because an electric mixer would increase the particle motion of the mixture more than whisking by hand.

What is an example of an insoluble substance?

quartz

Which of the following substances is insoluble in water?

quartz

What effect does increased temperature have on the solubility of substances?

The effect of temperature varies by substance. Solids are likely to become more soluble as temperature increases, while gases would become less soluble.

List the factors that affect the solubility of substances, or the rate at which they dissolve.

• polarity • surface area • motion • temperature • pressure

What are some of the ways that the concentration of a solution can be calculated?

• volume percent • mass percent • mass-volume percent

Generally speaking, what effect does temperature have on the solubility of gases in liquids?

As temperature increases, the solubility of the gases decreases

Examine the scenario, then answer the two following questions. Steve got distracted during a chemistry demonstration, and forgot to add salt crystals to his solution. He needs the crystals to dissolve more quickly so he can move on to the next step and catch up with the class. How can he take advantage of surface area to speed up his experiment?

If he breaks the crystals into smaller pieces first, they will have a greater surface area compared to their volume; this means more of each crystal can come into contact with the solvent at a time, and the crystals will dissolve more quickly.

Examine the scenario, then answer the two following questions. Steve got distracted during a chemistry demonstration, and forgot to add salt crystals to his solution. He needs the crystals to dissolve more quickly so he can move on to the next step and catch up with the class. What can he do to take advantage of motion to speed up his experiment?

If he stirs the crystals as they dissolve, it will bring more of the solvent in contact with the solute and crystals will dissolve more quickly.

Which statement correctly describes a supersaturated solution?

More solute than is normally possible is dissolved in the solution.

Which factors affect the solubility or dissolving rate of a substance?

Pressure Temperature Surface area Polarity

Examine the incomplete statement below. In order to make an unsaturated solution into a saturated solution, a scientist should __________. Which answer correctly completes the statement?

add more solute to the solution

Examine the incomplete statement below. A __________ solution contains a lot of dissolved solute for a given volume, whereas a __________ solution contains very little. Which set of words correctly completes the statement?

concentrated; dilute

Which factors affect solubility or the rate a substance dissolves by increasing the kinetic energy of the solution?

temperature and motion

In which of the following scenarios would it be most appropriate to use ppm to describe the concentration of the solutes in a solution? (Select all that apply.)

when describing environmental contaminants & when describing very dilute solutions