Liquids and Solutions - AP Chemistry
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Which equation accurately describes what happens to the boiling point when a solute is added to a liquid? (K = constant, M = molarity, m = molality)
Which equation accurately describes what happens to the boiling point when a solute is added to a liquid? (K = constant, M = molarity, m = molality)
The correct answer choice is the equation for boiling point elevation when solute is added to a solvent.
The correct answer choice is the equation for boiling point elevation when solute is added to a solvent.
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What is the freezing point of a solution with 
of sodium chloride in 
of water?
What is the freezing point of a solution with
The equation for freezing point depression is 
, where 
is the change in temperature, 
is a constant related to the solvent, 
is molality, and 
is the van't Hoff factor, which is the number of ion particles from each dissolved molecule. We simply plug these numbers into the equation to find the new freezing point.
We know our constant is 
. Molality is moles of solute per kilogram of solution, and we know that the density of water is one kilogram per liter and the molecular weight of sodium chloride is 
.
The van't Hoff factor is 
. Sodium chloride creates only two ions when dissolved, one 
and one 
.
Using these values, we can solve for the freezing point depression.
The freezing point will be decreased by 
. The normal freezing point is 
, making the new freezing point 
.
The equation for freezing point depression is
We know our constant is
The van't Hoff factor is
Using these values, we can solve for the freezing point depression.
The freezing point will be decreased by
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What is the freezing point of a 2M solution of 
in water?
What is the freezing point of a 2M solution of
First, we need to calculate the molality because that is what we use in our equation for freezing point depression. We can get that from the molarity without knowing exactly how many liters or grams we have. We just have to know what we have one mole per liter. The weight of water is one kilogram per liter, so this allows us to make this conversion.
The molality is 2m. The van't Hoff factor is 3, as we get one calcium ion and two chloride ions per molecule during dissociation.
We can now plug the values into the equation for freezing point depression.
This gives us our depression of 
. The normal freezing point of pure water is 
, which means our new freezing point is 
.
First, we need to calculate the molality because that is what we use in our equation for freezing point depression. We can get that from the molarity without knowing exactly how many liters or grams we have. We just have to know what we have one mole per liter. The weight of water is one kilogram per liter, so this allows us to make this conversion.
The molality is 2m. The van't Hoff factor is 3, as we get one calcium ion and two chloride ions per molecule during dissociation.
We can now plug the values into the equation for freezing point depression.
This gives us our depression of
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What is the new freezing point of 3L of aqueous solution that contains 
of 
and 
of 
?
What is the new freezing point of 3L of aqueous solution that contains
The important thing to remember for this question is that it doesn't matter what the solutes are in freezing point depression, just how many ions are created during dissociation. First, we need to convert our solute amounts to moles.
The molality of the solution is the moles of solute per kilogram of solvent. Since water has a density of one kilogram per liter, we can simply divide the total moles by the liters of solution. The molality of the solution is 
.
We can treat this solution as 3L of water containing 4mol of a solute that dissolves into a total of 5 ions. It does not matter which compound the ions come from, only that they end up in solution in the correct proportion. 2mol of calcium chloride will contribute 3 ions per molecule and 2mol of sodium chloride will contribute 2 ions per molecule, for a total of 5 ions per mole of solution.
Using these conclusions, we can solve the freezing point depression.
Our depression is then 
. Since the freezing point of pure water is 
, our new temperature for freezing point is 
.
The important thing to remember for this question is that it doesn't matter what the solutes are in freezing point depression, just how many ions are created during dissociation. First, we need to convert our solute amounts to moles.
The molality of the solution is the moles of solute per kilogram of solvent. Since water has a density of one kilogram per liter, we can simply divide the total moles by the liters of solution. The molality of the solution is
We can treat this solution as 3L of water containing 4mol of a solute that dissolves into a total of 5 ions. It does not matter which compound the ions come from, only that they end up in solution in the correct proportion. 2mol of calcium chloride will contribute 3 ions per molecule and 2mol of sodium chloride will contribute 2 ions per molecule, for a total of 5 ions per mole of solution.
Using these conclusions, we can solve the freezing point depression.
Our depression is then
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The vapor pressure of ethanol at room temperature is 45mmHg. A nonvolatile solute is added to a vial of ethanol, resulting in a solution with a vapor pressure of 34mmHg. What is the molar fraction of the nonvolatile solute in the solution?
The vapor pressure of ethanol at room temperature is 45mmHg. A nonvolatile solute is added to a vial of ethanol, resulting in a solution with a vapor pressure of 34mmHg. What is the molar fraction of the nonvolatile solute in the solution?
A nonvolatile solute will not contribute to the vapor pressure of a solution, and will only act to decrease the vapor pressure of the pure solvent. The molar fraction of the solvent in the solution can be determined using Raoult's law.
The solution's vapor pressure is equal to the vapor pressure of the pure solvent multiplied by the molar fraction of solvent in solution.
This means that the molar fraction of solvent in the solution is 0.76. As a result, we conclude that the molar fraction of solute in the solution is 0.24, since the sum of the mole fractions must equal 1.
A nonvolatile solute will not contribute to the vapor pressure of a solution, and will only act to decrease the vapor pressure of the pure solvent. The molar fraction of the solvent in the solution can be determined using Raoult's law.
The solution's vapor pressure is equal to the vapor pressure of the pure solvent multiplied by the molar fraction of solvent in solution.
This means that the molar fraction of solvent in the solution is 0.76. As a result, we conclude that the molar fraction of solute in the solution is 0.24, since the sum of the mole fractions must equal 1.
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A volatile solute with a vapor pressure of 23mmHg is added to a solvent with a vapor pressure of 85mmHg. What is the molar fraction of the solvent if the solution has a vapor pressure of 68mmHg?
A volatile solute with a vapor pressure of 23mmHg is added to a solvent with a vapor pressure of 85mmHg. What is the molar fraction of the solvent if the solution has a vapor pressure of 68mmHg?
Since the solute is volatile, it will contribute to the total vapor pressure of the solution. As a result, we must incorporate it when solving for the total vapor pressure.
We can find the vapor pressures using Raoult's law.
Since we are solving for the molar fraction of the solvent, we will designate its molar fraction as 
. The sum of the molar fractions of each component must be equal to 1; thus, the molar fraction of the solute must be 
. Using these variables and the information given, we can solve for the molar fraction of the solvent.
Since the solute is volatile, it will contribute to the total vapor pressure of the solution. As a result, we must incorporate it when solving for the total vapor pressure.
We can find the vapor pressures using Raoult's law.
Since we are solving for the molar fraction of the solvent, we will designate its molar fraction as
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What is the boiling point of a solution created when four moles of glucose are dissolved in two kilograms of water?
Assume that glucose is a nonvolatile solute.
What is the boiling point of a solution created when four moles of glucose are dissolved in two kilograms of water?
Assume that glucose is a nonvolatile solute.
Since the glucose is nonvolatile, we can use the boiling point elevation equation to solve for the new boiling point.
Since glucose does not ionize in water, the van't Hoff factor is simply 1 for this problem. The molality can be found by the moles of solute per kilogram of solvent.
This means that the boiling point for the water will be elevated by 1.03oC with the addition of the glucose. Since pure water has a boiling point of 100oC, the boiling point for this solution is 101.03oC.
Since the glucose is nonvolatile, we can use the boiling point elevation equation to solve for the new boiling point.
Since glucose does not ionize in water, the van't Hoff factor is simply 1 for this problem. The molality can be found by the moles of solute per kilogram of solvent.
This means that the boiling point for the water will be elevated by 1.03oC with the addition of the glucose. Since pure water has a boiling point of 100oC, the boiling point for this solution is 101.03oC.
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50g of an unknown compound are added to three kilograms of water. The compound is nonvolatile, and has a van't Hoff factor of 2. It is determined that the solution has a freezing point of 
.
What is the molar mass of the unknown compound?
50g of an unknown compound are added to three kilograms of water. The compound is nonvolatile, and has a van't Hoff factor of 2. It is determined that the solution has a freezing point of
What is the molar mass of the unknown compound?
In order to solve for the molar mass of the unknown compound, we need to use the freezing point depression equation.
Since molality is equal to the moles of solute divided by the kilograms of solvent, we can substitute the moles of solute with the mass of the solute divided by the molar mass of the solute.
This allows us to solve for the molar mass of the compound using a substituted equation.
We can use the values given in the question to solve for the molar mass.
In order to solve for the molar mass of the unknown compound, we need to use the freezing point depression equation.
Since molality is equal to the moles of solute divided by the kilograms of solvent, we can substitute the moles of solute with the mass of the solute divided by the molar mass of the solute.
This allows us to solve for the molar mass of the compound using a substituted equation.
We can use the values given in the question to solve for the molar mass.
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Which of the following solutions has the highest boiling point?
Assume that all solutes in solution are nonvolatile.
Which of the following solutions has the highest boiling point?
Assume that all solutes in solution are nonvolatile.
The equation for boiling point elevation is 
.
Since all of the solutions are aqueous, we do not need to consider the boiling point elevation constant (
) when comparing the solutions. The two factors we need to consider are molality (
) and the van't Hoff factor (
) of the solute.
Glucose will not ionize in solution, sodium chloride will make two ions in solution, and magnesium chloride will make three ions in solution.
When multiplying the molality by the van't Hoff factor, we can determine that the magnesium chloride solution will elevate the boiling point by the highest number.
The equation for boiling point elevation is
Since all of the solutions are aqueous, we do not need to consider the boiling point elevation constant (
Glucose will not ionize in solution, sodium chloride will make two ions in solution, and magnesium chloride will make three ions in solution.
When multiplying the molality by the van't Hoff factor, we can determine that the magnesium chloride solution will elevate the boiling point by the highest number.
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It is snowing outside and you decide to throw salt onto the driveway. What is the purpose of throwing salt onto the driveway?
It is snowing outside and you decide to throw salt onto the driveway. What is the purpose of throwing salt onto the driveway?
When a solid is dissolved into a liquid, in our case water (snow), the freezing point will decrease. This phenomenon is called freezing point depression. In order to freeze, the molecules of the liquid must organize into a relatively static lattice. This highly organized structure is disrupted by the presence of extra molecules and ions that are dissolved in the liquid, making it harder to transition to a solid.
With enough salt in the snow, the freezing point will depress below the current temperature, leading the snow to melt and be in the liquid phase. The salt ions will infiltrate the ice/snow lattice, breaking apart the solid and cause the water to remain liquid.
When a solid is dissolved into a liquid, in our case water (snow), the freezing point will decrease. This phenomenon is called freezing point depression. In order to freeze, the molecules of the liquid must organize into a relatively static lattice. This highly organized structure is disrupted by the presence of extra molecules and ions that are dissolved in the liquid, making it harder to transition to a solid.
With enough salt in the snow, the freezing point will depress below the current temperature, leading the snow to melt and be in the liquid phase. The salt ions will infiltrate the ice/snow lattice, breaking apart the solid and cause the water to remain liquid.
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You are attempting to distill the water from a sample of seawater. What can you do to facilitate the process?
You are attempting to distill the water from a sample of seawater. What can you do to facilitate the process?
Dissolving solutes into a solvent will influence the movement of the molecules in solution. In a pure solvent, the molecules are essentially in uniform motion. When an impurity is added, such as salt in seawater, the foreign particles begin to interact with the solvent. Different masses, velocities, and attractive forces alter the patterns of the liquid molecules and cause an overall decrease in their energy. Transitioning to a gaseous state from a liquid state requires a reduction of intermolecular forces, while adding solute increases these forces in the solution. Adding solute thus inhibits the transition from liquid to gas, resulting in boiling point elevation.
Filtering the water to remove some solute could help to distill the water by removing some of the boiling point elevation. Moving to the lower elevation or increasing the pressure will increasing the boiling point.
Dissolving solutes into a solvent will influence the movement of the molecules in solution. In a pure solvent, the molecules are essentially in uniform motion. When an impurity is added, such as salt in seawater, the foreign particles begin to interact with the solvent. Different masses, velocities, and attractive forces alter the patterns of the liquid molecules and cause an overall decrease in their energy. Transitioning to a gaseous state from a liquid state requires a reduction of intermolecular forces, while adding solute increases these forces in the solution. Adding solute thus inhibits the transition from liquid to gas, resulting in boiling point elevation.
Filtering the water to remove some solute could help to distill the water by removing some of the boiling point elevation. Moving to the lower elevation or increasing the pressure will increasing the boiling point.
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The vapor pressure of water is 
at 
. Two moles of a nonvolatile solute are added to eight moles of water. What is the vapor pressure of this solution?
The vapor pressure of water is
A nonvolatile solute will not contribute to the vapor pressure of the solution, but will decrease the vapor pressure of the pure solvent. We can solve for the vapor pressure of the solution by using Raoult's law:
In other words, the new vapor pressure is equal to the molar fraction of the solvent multiplied by the vapor pressure of the pure solvent.
A nonvolatile solute will not contribute to the vapor pressure of the solution, but will decrease the vapor pressure of the pure solvent. We can solve for the vapor pressure of the solution by using Raoult's law:
In other words, the new vapor pressure is equal to the molar fraction of the solvent multiplied by the vapor pressure of the pure solvent.
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At room temperature, hexane has a vapor pressure of 
and ethanol has a vapor pressure of 
. A solution of these two solvents at room temperature has a vapor pressure of 
. What percentage of the solution is ethanol?
At room temperature, hexane has a vapor pressure of
Since both of the solvents have a vapor pressure, we can find the percentage of ethanol in the solution by using Raoult's law, including both solvents in the equation:
Since we want to find the percentage of ethanol in the solution, we will designate the molar fraction of ethanol as 
. Since the sum of the molar fractions equals one, the molar fraction of hexane will be designated as 
.
So, 63.4% of the solution is ethanol.
Since both of the solvents have a vapor pressure, we can find the percentage of ethanol in the solution by using Raoult's law, including both solvents in the equation:
Since we want to find the percentage of ethanol in the solution, we will designate the molar fraction of ethanol as
So, 63.4% of the solution is ethanol.
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What is the melting point of a 
aqueous solution that contains 
of 
?
What is the melting point of a
Since a salt has been added to the pure water, we can find the new melting point of the solution by using the freezing point depression equation:
The change in temperature is equal to the freezing point constant for the solvent multiplied by the molality of the solution multiplied by the van't Hoff factor. The van't Hoff factor is the number of ions that a salt will dissociate into when in solution.
For this particular salt, the van't Hoff factor is three. The molality will be equal to the moles of solute over the mass of the solvent.
Using these terms together in the original equation, we can find the freezing point depression.
This is the change in temperature from the regular freezing point. Since the freezing point for pure water is 
, the new melting point is 
.
Since a salt has been added to the pure water, we can find the new melting point of the solution by using the freezing point depression equation:
The change in temperature is equal to the freezing point constant for the solvent multiplied by the molality of the solution multiplied by the van't Hoff factor. The van't Hoff factor is the number of ions that a salt will dissociate into when in solution.
For this particular salt, the van't Hoff factor is three. The molality will be equal to the moles of solute over the mass of the solvent.
Using these terms together in the original equation, we can find the freezing point depression.
This is the change in temperature from the regular freezing point. Since the freezing point for pure water is
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A solution of 
of water and 
of glucose has a freezing point depression of 
. Which of the following changes would NOT triple the original change in the melting point?
A solution of
For reference, the freeing point depression equation is:
Since we want to triple the melting point change, we need to manipulate the freezing point depression equation so that the value of is three times as large.
Replacing glucose with magnesium chloride will make the van't Hoff factor three, so the melting point change will triple.
Reducing the amount of water by a factor of three will also triple the melting point change, as will tripling the glucose amount.
Six moles of sodium chloride will triple the solute concentration and make the van't Hoff factor two. This multiplies the melting point change by six.
For reference, the freeing point depression equation is:
Since we want to triple the melting point change, we need to manipulate the freezing point depression equation so that the value of
Replacing glucose with magnesium chloride will make the van't Hoff factor three, so the melting point change will triple.
Reducing the amount of water by a factor of three will also triple the melting point change, as will tripling the glucose amount.
Six moles of sodium chloride will triple the solute concentration and make the van't Hoff factor two. This multiplies the melting point change by six.
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Which equation accurately describes what happens to the boiling point when a solute is added to a liquid? (K = constant, M = molarity, m = molality)
Which equation accurately describes what happens to the boiling point when a solute is added to a liquid? (K = constant, M = molarity, m = molality)
The correct answer choice is the equation for boiling point elevation when solute is added to a solvent.
The correct answer choice is the equation for boiling point elevation when solute is added to a solvent.
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What is the freezing point of a solution with of sodium chloride in of water?
What is the freezing point of a solution with
The equation for freezing point depression is , where is the change in temperature, is a constant related to the solvent, is molality, and is the van't Hoff factor, which is the number of ion particles from each dissolved molecule. We simply plug these numbers into the equation to find the new freezing point.
We know our constant is . Molality is moles of solute per kilogram of solution, and we know that the density of water is one kilogram per liter and the molecular weight of sodium chloride is .
The van't Hoff factor is . Sodium chloride creates only two ions when dissolved, one and one .
Using these values, we can solve for the freezing point depression.
The freezing point will be decreased by . The normal freezing point is , making the new freezing point .
The equation for freezing point depression is
We know our constant is
The van't Hoff factor is
Using these values, we can solve for the freezing point depression.
The freezing point will be decreased by
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What is the freezing point of a 2M solution of in water?
What is the freezing point of a 2M solution of
First, we need to calculate the molality because that is what we use in our equation for freezing point depression. We can get that from the molarity without knowing exactly how many liters or grams we have. We just have to know what we have one mole per liter. The weight of water is one kilogram per liter, so this allows us to make this conversion.
The molality is 2m. The van't Hoff factor is 3, as we get one calcium ion and two chloride ions per molecule during dissociation.
We can now plug the values into the equation for freezing point depression.
This gives us our depression of . The normal freezing point of pure water is , which means our new freezing point is .
First, we need to calculate the molality because that is what we use in our equation for freezing point depression. We can get that from the molarity without knowing exactly how many liters or grams we have. We just have to know what we have one mole per liter. The weight of water is one kilogram per liter, so this allows us to make this conversion.
The molality is 2m. The van't Hoff factor is 3, as we get one calcium ion and two chloride ions per molecule during dissociation.
We can now plug the values into the equation for freezing point depression.
This gives us our depression of
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What is the new freezing point of 3L of aqueous solution that contains of and of ?
What is the new freezing point of 3L of aqueous solution that contains
The important thing to remember for this question is that it doesn't matter what the solutes are in freezing point depression, just how many ions are created during dissociation. First, we need to convert our solute amounts to moles.
The molality of the solution is the moles of solute per kilogram of solvent. Since water has a density of one kilogram per liter, we can simply divide the total moles by the liters of solution. The molality of the solution is .
We can treat this solution as 3L of water containing 4mol of a solute that dissolves into a total of 5 ions. It does not matter which compound the ions come from, only that they end up in solution in the correct proportion. 2mol of calcium chloride will contribute 3 ions per molecule and 2mol of sodium chloride will contribute 2 ions per molecule, for a total of 5 ions per mole of solution.
Using these conclusions, we can solve the freezing point depression.
Our depression is then . Since the freezing point of pure water is , our new temperature for freezing point is .
The important thing to remember for this question is that it doesn't matter what the solutes are in freezing point depression, just how many ions are created during dissociation. First, we need to convert our solute amounts to moles.
The molality of the solution is the moles of solute per kilogram of solvent. Since water has a density of one kilogram per liter, we can simply divide the total moles by the liters of solution. The molality of the solution is
We can treat this solution as 3L of water containing 4mol of a solute that dissolves into a total of 5 ions. It does not matter which compound the ions come from, only that they end up in solution in the correct proportion. 2mol of calcium chloride will contribute 3 ions per molecule and 2mol of sodium chloride will contribute 2 ions per molecule, for a total of 5 ions per mole of solution.
Using these conclusions, we can solve the freezing point depression.
Our depression is then
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The vapor pressure of ethanol at room temperature is 45mmHg. A nonvolatile solute is added to a vial of ethanol, resulting in a solution with a vapor pressure of 34mmHg. What is the molar fraction of the nonvolatile solute in the solution?
The vapor pressure of ethanol at room temperature is 45mmHg. A nonvolatile solute is added to a vial of ethanol, resulting in a solution with a vapor pressure of 34mmHg. What is the molar fraction of the nonvolatile solute in the solution?
A nonvolatile solute will not contribute to the vapor pressure of a solution, and will only act to decrease the vapor pressure of the pure solvent. The molar fraction of the solvent in the solution can be determined using Raoult's law.
The solution's vapor pressure is equal to the vapor pressure of the pure solvent multiplied by the molar fraction of solvent in solution.
This means that the molar fraction of solvent in the solution is 0.76. As a result, we conclude that the molar fraction of solute in the solution is 0.24, since the sum of the mole fractions must equal 1.
A nonvolatile solute will not contribute to the vapor pressure of a solution, and will only act to decrease the vapor pressure of the pure solvent. The molar fraction of the solvent in the solution can be determined using Raoult's law.
The solution's vapor pressure is equal to the vapor pressure of the pure solvent multiplied by the molar fraction of solvent in solution.
This means that the molar fraction of solvent in the solution is 0.76. As a result, we conclude that the molar fraction of solute in the solution is 0.24, since the sum of the mole fractions must equal 1.
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