Solutions• The inward pull that tends to

minimize the surface is called surface tension. Surface tension acts like a thin skin.

• A liquid that has strong intermolecular attractions has a high surface tension.

• The surface tension of water is higher than the surface tensions of most other liquids.

• Hydrogen bonding is primarily responsible for the surface tension of water.

• A surfactant interferes with hydrogen bonding and reduces surface tension. Soaps and detergents are surfactants. Detergents decrease the surface tension of water.

• As a general rule, solids sink in their own liquids.

• Ice floats on liquid water because its density is lower than that of liquid water. This is because the hydrogen bond framework in the ice crystals collapses and water molecules pack closer together.

• A solution is a homogeneous mixture. It has the same composition throughout. A solvent dissolves the solute.

• If salt is dissolved in water, water serves as the solvent and salt is the solute.

• An aqueous solution is water that contains dissolved substances.

• As a general rule, like dissolves like.• Substances that dissolve very readily in water

include ionic compounds (NaOH) and polar covalent molecules.

• Grease is nonpolar and does not dissolve in water.

• Grease would be expected to dissolve readily in the nonpolar solvent CCl4 as well as gasoline.

• Mixtures from which some of the particles will settle slowly upon standing are referred to as suspensions.

• Particles in a colloid are smaller than those in a suspension and larger than those in a solution. Smoke is an example of a colloid.

• Sometimes water molecules are an important part of a crystal structure. A compound that contains water in its crystals is called a hydrate. Chemists write the formula of a hydrate with a dot to connect the formula of the compound and the number of water molecules per formula unit.

• Determine the percent by mass of water in CuSO4 5H2O.

• Mass 5H2O = 5 X 18 = 90.0 g

• Mass of CuSO4 = – Cu = 63.5– S = 32.1– O4 = 16 X 4– 159.6 g

• Mass of hydrate = 90.0 g + 159.6 g• Mass of hydrate = 249.6 g

%100hydrateofmass

OHofmassOH% 2

2

%100g6.249

g0.90OH% 2

OH%1.36OH% 22

• Determine the percent by mass of water in Na2SO4 10H2O.

• 142.1 g + 180.0 g

OHg

g

hydrateofmass

OHofmassOH 2

22 %9.55%100

1.322

0.180%100%

• Hygroscopic hydrates remove moisture from the air to form higher hydrates. Hygroscopic substances have low vapor pressures, remove moisture from the air, and can be used as drying agents.

• The rate at which a solute dissolves in a given solvent is determined by the extent to which the solution is agitated, the temperature of the solution, and the size of the solute particles.

• Agitating the solution usually makes a substance dissolve faster in a solvent.

• In general, as the temperature of a solvent increases, the solubility of any gas dissolved in that solvent decreases.

• A saturated solution contains the maximum amount of solute for a given quantity of solvent.

• A glass of iced tea containing excess sugar at the bottom is said to be saturated.

• A supersaturated solution contains more solute than it can theoretically hold. Crystallization can occur if the inside of the container is scratched or another crystal is added. If a crystal added to an aqueous solution causes many particles to come out of the solution, the original solution was supersaturated.

• Henry’s Law –

• Where S1, S2 – solubility of gas in a liquid and P1, P2 – pressure above the liquid

• Increasing the pressure of the gas above the solution would increase the solubility of a gas in a liquid.

2

2

1

1

P

S

P

S

• At 10C, the solubility of a gas in water is 2.45g/L at 0.750 atm.

• What pressure would be required to produce an aqueous solution containing 6.25 g/L of this gas at 10C?

• P2 = ? S1 = 2.45g/L P1 = 0.750 atm S2 = 6.25 g/L

• P2 = 1.91 atm

2

2

1

1

P

S

P

S

2P

L/g25.6

atm750.0

L/g45.2

• The concentration is a measure of the amount of solute dissolved in a solvent. A dilute solution contains a small amount of solute.

• In a concentrated solution there is a large amount of solute.

• Molarity is a measure of concentration.

• If the molarity is greater, then the solution is more concentrated.

• A 0.25M solution is more concentrated than a 0.23M solution.

solutionofliters

soluteofmoles)M(Molarity

• Calculate the molarity of a solution that contains 50.0 g of Mg(NO3)2 per 225 mL of solution.

M50.1)NO(Mgg3.148

)NO(Mgmol1

L

mL1000

mL225

)NO(Mgg0.50

23

2323

• How many moles of solute are present in 4.00 L of a 2.0M NaNO3 solution?

• Moles of solute = ? Molarity = 2.0M liters of solution = 4.00 L

• moles of solute = 8.0 mol

solutionofliters

soluteofmoles)M(Molarity

L00.4

soluteofmolesNaNOM0.2 3

• The mole fraction (X) is the number of moles of solute (nA) or solvent (nB) in the solution (nA + nB).

• What is the mole fraction of ethanol in a solution containing 1.5 moles of ethanol and 3.0 mol of water?

• XA = ? nA = 1.5 mol nB = 3.0 mol

BA

AA nn

nX

BA

BB nn

nX

BA

AA nn

nX

33.

mol0.3mol5.1

mol5.1XA

• Concentration involving a solid is often expressed as a percent by mass.

• What is the percent (m/m) of a solution containing 20. g of NaCl in 400. g of solution?

• % (m/m) = ? mass of solute = 20. g mass of solution = 400. g

%100solutionofmass

soluteofmass)m/m(massbyPercent

%0.5%100g.400

g.20)m/m%(

• If a saturated solution of AgNO3 at 20C contains 216 g AgNO3 per 100.0 g of water, what mass of water could contain 725 g of this solute at the same temperature?

OHg336AgNOg725AgNOg216

OHg0.10023

3

2

• Another way of expressing concentration is molality or molal concentration.

• What is the molality of a solution prepared by dissolving 5.85 g of NaCl in 500. g of water?

solventofkg

soluteofmolesmolality

molal20.0NaClg5.58

NaClmol1

OHkg500.0

NaClg85.5

2

• What mass of AgNO3 would be required to prepare a 0.250 molal solution in 125 g of water?

33

332 AgNOg31.5

AgNOmol1

AgNOg9.169

g1000

AgNOmol250.0OHg125

• The presence of a solute in a given solvent causes the vapor pressure of the solution to be lower than that of the pure solvent. This makes the boiling temperature higher.

• The presence of a solute disrupts crystal formation. This causes the freezing temperature of a solution to be lower than that of the pure solvent. The addition of antifreeze to water in a car radiator causes the freezing point of the mixture to decrease.