Chemistry B Lesson 4 Solutions

What is the percent by volume of a solution formed by adding 12 L of acetone to 29 L of water?

• 29%

• 60%

• 41%

• 15%

Answer explanation

Percent by volume = volume of solute/volume of solution x 100% = 12L/(29L+12L) x 100 = 29%.

The solubility of a gas increases as

• the temperature increases

• the solvent becomes more polar

• the pressure decreases

• the pressure increases

Answer explanation

The solubility of a gas increases as the pressure increases. 

You can dilute a solution by adding more _________.

• solvent

• solute

Answer explanation

Dilute solutions have less solute to solvent.  To dilute a solution, add more solvent.

Colligative properties are important in solutions.  Which description below best describes colligative properties?

• Colligative properties are physical properties of a solution which depend only upon the number of solute particles but not upon their identity.

• Colligative properties which are a result of the number of protons in the nucleus of the atoms.

• Colligative properties are chemical properties of specific polar solutes.

• Colligative properties are any properties which are present because of the polarity of the solute and solvent.

What volume would you need to dilute 0.2 L of a 15 M solution to obtain a 5 M solution?

• 3L

• 1L

• 0.2L

• 0.6L

Answer explanation

M₁V₁ = M₂V­₂ therefore V₂ = M₁V­₁/M₂ = (15M*0.2 L)/5M =0.6 L. 

Which statement below describes a supersaturated solution?

• A solution in which the rate of solute going into solution and the rate of solute leaving solution are equal.

• A solution which contains more dissolved solute than is theoretically possible at a given temperature.

• A solution which can become saturated faster than a speeding bullet.

• A solution which is capable of dissolving more solute than is currently in solution.

Answer explanation

A supersaturated solution is one which contains more dissolved solute than is theoretically possible at a given temperature. It is made by making a saturated solution at a higher temperature and then allowing the solution to cool.

In order to calculate the molality of a solution, which two quantities must be known?

 

• The mass of the solute and the volume of the solvent.

• The number of moles of the solute and the mass of the solvent.

• The number of moles of the both the solute and solvent.

• The mole ratio of both the solute and solvent and the volume of the solution.

Answer explanation

The molality is defined as the number of moles of solute divided by the kilograms of solvent.

MgCl₂ is a salt used to treat icy roads.  Why does the salt help in these conditions?

• MgCl₂ raises the freezing point of water melting the ice

• MgCl₂ sticks to the car tires better

• MgCl₂ lowers the freezing point of water melting the ice

• MgCl₂ raises the vapor pressure melting the ice

Answer explanation

MgCl₂ dissolves into the ice and water on the roads, lowering the freezing point of water and melting the ice. 

If the number of moles of solute in a solution is increased which combination of changes in the colligative properties of the solution are we likely to see?

• The boiling point and vapor pressure will be lower; the freezing point will be higher.

• The boiling point will rise; the vapor pressure and freezing point will lower.

• The boiling point, vapor pressure, and freezing point of the solution will all lower.

• The boiling point, vapor pressure, and freezing point of the solution will all rise.

Answer explanation

When the number of solute particles are increased, the boiling point of the solution is raised, the vapor pressure and freezing point of the solution are lowered. (

How is solubility determined?

• By determining the maximum mass of a solute that can be dissolved in 100g of a solvent at a given temperature and pressure.

• By determining the maximum mass of a solvent that can be dissolved in 100g of a solute at a given temperature and pressure.

• By determining the minimum mass of a solute that can be dissolved in 100g of a solvent at a given temperature and pressure.

• By determining the mass of a solute in 100g of a solvent.

Answer explanation

Solubility is the maximum mass of a solute that can be dissolved in 100g of a solvent at a given temperature and pressure.