Physical Properties of Solutions Chapter 12

Objectives 1.0 Define key terms and concepts. 1.8 Explain how a solute and solvent interact to make a solution. 1.9 Determine the properties of a solution and predict how the solution will interact with other solutions Determine the concentration of a solution using molarity, molality, and percent concentration Explain how to properly prepare a solution of a specific concentration.

Objectives 1.12 Explain the effects of temperature and pressure on solubility Explain how distillation works Apply Henry’s Law to determine the solubility of a gas in a solution Determine how a solute affects the boiling point and freezing point of a solution Calculate the molar mass of a solute using boiling point elevation and freezing point depression.

Solutions Solution  Homogeneous mixture composed of two or more substances Solute  What is dissolved in the solution Solvent  Does the dissolving Salt Water Chocolate Milk

Solutions Aqueous Solution  Solution in which water is the solvent Dilute Solution  Solution that contains a little bit of solute and a lot of solvent  Saline Solution Concentrated Solution  Solution that contains a lot of solute and little solvent

Solutions Saturated Solutions  A solution that contains the maximum amount of solute that a solvent can dissolve at a given temperature Unsaturated Solutions  A solution contains less than the maximum amount of solute that a solvent can dissolve at a given temperature Supersaturated Solutions  A solution contains more solute that a saturates solution Crystallization  The process by which a solute comes out of solution and forms crystals.

Solutions Three types of interactions in solutions  Solvent-Solvent Interaction  Solute-Solute Interaction  Solvent-Solute Interaction How a solution is formed  The solvent molecules separate  The solute molecule separate  The solute and solvent molecules mix

Solutions Molarity (M)  The amount of solute in moles divided by the amount of solvent measured in Liters  Another way to measure concentration  Measured in moles per Liter (mol/L) Moles Molarity x Volume

What is the molarity of a solution containing 3.2 moles of NaCl dissolved in 0.56L of solute.

If 7.9g of KI are dissolved in 500mL of water, what is the concentration of the solution?

How many grams of copper (II) nitrate need to be dissolved in 1.5L of water to produce a 0.25M solution?

Percent Concentration What is the percent by mass of a solution containing 3.6g salt and 10.8g water?

What is the percent by mass of 8.1g of solution containing 2.7g KI? What is the percent by mass of a solution containing 100g of water and 10g of HCl?

If 35mL of HCl are dissolved in 250mL of water, what is the percent by volume of HCl present? What is the percent by volume of a 300mL solution containing 239mL ethanol?

500g aqueous solution is 21% sodium chloride. How many grams of solute and solvent are present in the solution?

A laboratory procedure requires you to use 250mL of a 30% hydrochloric acid solution. Calculate how many mL of HCl are present in this solution?

Molality Molality (m)  The number of moles of solute dissolved in 1kg of solvent. Moles of Solute Molality Mass of Solvent x

If 5.9g of calcium bromide is dissolved in 500g of water, what is the molality of the solution?

How many moles of solute are dissolved in 850g of solvent to produce a 0.125m solution?

If 0.70moles of NaOH is dissolved in 1.2L of water, what is the molality of the solution?

If 10.6g of potassium permanganate is dissolved in 1.3L of ethanol, what is the molality of the solution? The density of ethanol is 0.789g/mL.

What Are Your Questions?

Temperature and Solubility Solubility of Solids  The solute typically become more soluble in a solvent as the temperature increases

Temperature and Solubility Solubility of Gasses  The solute (gas) typically becomes less soluble in a solvent as the temperature increases Thermal Pollution  The heating of waterways to a temperature that is harmful to it’s inhabitants.

Pressure and Solubility Pressure does not effect the solubility of liquids and solids, but it does gasses. As pressure increases, the solubility of gasses typically increases in a liquid. Henry’s Law  The solubility of a gas in a liquid is directly proportional to the pressure of the gas in the solution.  c is the concentration in moles/L  P is pressure in atm  k is a constant in mole/L x atm c = kP

Pressure and Solubility

The solubility of a gas in water at 1.2atm and 25°C is 7.5x10 -4 mole/L. What is the Henry’s Law constant for this gas? What is the solubility of the gas at 0.75atm?

If 27g of ethyne will dissolve in 1L of water at 1.0atm, what is the solubility of ethyne in water at 3.6atm?

How many grams of oxygen will dissolved in 1.75L of water at 600mmHg and 25°? The Henry’s constant for oxygen is 1.3x10 -3 mole/L·atm.

Colligative Properties  Properties of solutions that depend on the number of solute particles in solution and not on the nature of the solute particles. Vapor Pressure Lowering  Relates solution vapor pressure to the concentration of the nonvolatile solute present.  Raoult’s Law  Where P 1 is the vapor pressure of the solvent over a solution  P° 1 is the vapor pressure of the pure solvent  X 1 is the mole fraction of the solvent in solution  X 2 is the mole fraction of the solute P 1 = X 1 P° 1 P° 1 - P 1 = ΔP = X 2 P° 1

What is the vapor-pressure lowering of water when 5.67g of glucose, C 6 H 12 O 6, is dissolved in 25.2g of water at 25°C? What is the vapor pressure of the solution? The vapor pressure of water is 23.8mmHg at 25°C.

If 0.515g of Naphthalene, C 10 H 8, is dissolved in 60.8g of chloromethane, what is the vapor-pressure lowering of chloromethane at 20°C from the naphthalene if the vapor pressure of chloromethane at 20°C is 156mmHg? Calculate the vapor pressure of the solution?

Simple Distillation Fractional Distillation Distillation

Colligative Properties Boiling Point Elevation  A liquid boils at the point its vapor pressure is equal to the external pressure (atmospheric pressure)  If a nonvolatile solute lowers the vapor of a solution, then it would need more energy to boil, hence have a higher boiling point.  Where ΔT b is the boiling point elevation  T b is the boiling point of the solution  T° b is the boiling point of the pure substance  m is molality  K b is the molal boiling-point elevation constant, in °C/m ΔT b = K b m ΔT b = T b -T° b

Colligative Properties Freezing Point Depression  When the addition of a solute decreases the freezing point of a solution.  Where ΔT f is the freezing point elevation  T f is the freezing point of the solution  T° f is the freezing point of the pure substance  m is molality  K f is the molal freezing-point depression constant, in °C/m ΔT f = K f m ΔT f = T f -T° f

Colligative Properties

If an aqueous solution contains 0.020m glucose, what is the boiling point and freezing points of the solution? The K b and K f of water are 0.512°C/m and 1.86°C/m, respectively.

How many grams of ethylene glycol, CH 2 OHCH 2 OH, need to be added to 37.8g of water for the solution to have a freezing point of -1.2°C? The K b and K f of water are 0.512°C/m and 1.86°C/m, respectively.

A solution is prepared by dissolving 0.313g of a substance in 25.4g of water. The molality of the solution is determined using freezing point depression to be 0.056m. What is the molecular weight of the substance?

A 0.930g of vitamin C was dissolved in 95.0g of water. The concentration of vitamin C in solution was determined to be m using depression point freezing. What is the molecular weight of this compound?

A 0.205g sample of a compound was dissolved in 25.0g of water. The boiling point elevation of the solution was found to be 0.159°C. What is the molecular weight of the compound in solution? The K b of water is 0.512°C/m.

Colligative Properties So far we have only talked about nonelectrolyte solutions, where the solute doesn’t ionize. The concentration of electrolyte solutions will be affected depending on the number of ions in solutions. The greater the concentration of ions in solution, the higher the boiling point/lower the freezing point. van’t Hoff Factor (i)  Relates number of particles that will dissolve in solution after dissociation to number of particles that were initially dissolved in solution. ΔT f = iK f mΔT b = iK b m

An aqueous solution contains equal concentrations of the following ionic compounds LiCl, CaCl 2, Na 3 PO 4. Which solution will have the high boiling point? The lowest freezing point? Why?

Estimate the freezing point and boiling point of a 0.010m aqueous solution of aluminum sulfate. Assume the value of i is based on the formula of the compound.

Colligative Properties Osmosis  The net movement of solvent molecules through a semipermeable membrane from a pure solvent or a dilute solution to a more concentrated solution Osmotic Pressure (π)  The pressure needed to stop osmosis  Where R=0.0821L·atm/K·mole  M is molarity  T is temperature in K π= MRT

Osmosis

What is the osmotic pressure of a 1.8L solution containing 2.1g of NaCl at 30°C?

What Are Your Questions?