Properties of Solutions

Chemistry

Mrs. Stoops

Chapter Problems

p 565: 22, 30, 34, 38, 42, 44, 60, 62, 68, 76, 89, 92

Solutions• Solutions – homogeneous mixture can

be solid, liquid or gas• Solvent – the substance doing the

dissolving• Solute – the substance being dissolved• Solution Process – one substance

disperse another. Solute and solvent should have comparable IMF

• Solvation – surrounded by liquid molecules

• Hydration – solvent is water in solvation

Exothermic Vs Endothermic

Exothermic is spontaneous• Endothermic is nonspontaneous

* any process that decreases order is spontaneous

Equilibrium – forward reaction moves at the same rate as the reverse reaction. Shown with double headed arrow

Solubility

Solubility – ability to be dissolved• Every substance has a unique solubility depending on

temperature onlyUnsaturated – a solution that may dissolve more soluteSupersaturated – a solution with more solid than normally

allowed at the temperature – unstable. (the solution was heated and the was allowed to cool)

Factors Affecting Solubility

1. Temperature

2. Pressure

3. Nature of the substance (type of stuff)

Surface area

Vs.

Solute – Solute Interactions

• greater the solubility, the stronger the IMF– increase with mass and polarity

• Like dissolve Likes– Polar will dissolve polar substances only– Water is polar– Increasing the number of carbons lowers solubility of

water– Increasing the number of –OH groups (alcohol)

increases the solubility in water

Pressure – increasing pressure above a substance increases solubility in gases only. Solids and liquids are not affected. (ex soda)

Henry’s Law – solubility of gas increases in direct proportion to pressure above the solution

C = k P

C = concentration

K = Henry’s law constant

P = pressure

Temperature effects on solubility

• Solids –(most) solubility is directly proportionally (increase T, increase solubility)

• Gases – solubility decrease with increase in temperature

Solubility Curves

Concentration Units

• Mass Percent = mass of component in solution x 100

Total mass of solution

PPM – parts per million

1 ppm = 1 g per 106 g of solution

Ppm = mass of component x 106

total mass

Example units – 1mg/kg or 1 mg/L

PPB – parts per billion

• Similar to above but . . . billion (109)• 1 ppb = 1 g per 109 g solution• Example units – 1 g/L (micro gram)

Mole Fraction

X – all fractions in solution will equal one

No units

X = moles of component

Total moles of all parts of solutions

Molarity

most commonly used

M = moles of solute

L solution

Units – mol/L or M

Molality

m = moles of solute

kg of solvent

units – mol/kg or m

*** Be careful lots of M’s

ExampleCalculate the mass percent, ppm solute, and mole fraction

of solvent for a solution of HC2H3O2 that has a molality of 3.5.

3.5 mol solute1 kg solvent

3.5 mole x 60 g = 210 g solute 1 mole

Mass % = 210 g solute x 100 = 17.36% 1000 g + 210 g

Ppm = 210g x 106 = 173554 ppm 1210 g

1000 g H2O x 1 mole = 55.56 mole 18 g

Mole fraction = 55.56 mole = 0.941 55.56 + 3.5

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Homework

p 565: 29, 33, 37, 39, 41, 43, 45.

Other worksheets for practice

Colligative Properties

depends on concentration of substance, type is not important, number is!

1 Vapor Pressure

2 Freezing point depression

3 Boiling point elevation

4 Osmosis or osmotic pressure

Vapor Pressure• pressure above a solution in a closed container.

Nonvolatile solution have no vapor pressure (they do not evaporate)

• Adding a solution always lowers the vapor pressure• Based on concentration

Raoult’s Law PA = XA PºA

PA = partial pressure of AXA = Mole fraction of APºA = V.P. of pure solvent A

Boiling Point Elevation

• adding a nonvolatile solute raises the boiling point proportional to the number of particles

• NaCl Na+ + Cl- 2 particles

Tb = kb m

Tb = change in temp

Kb = boiling constant (page 490)

m = molality

Freezing Point Depression

• freezing point is lowered just like boiling point is elevated. Strictly based on number of particles

Tf = kf m

Tf = change in temp

Kf = freezing constant (page 490)

m = molality

Osmotic Pressure

• Osmosis – passage of particle through a membrane• Osmotic pressure is the force that prevents osmosis or

particles from moving through - osmotic pressure

= MRT or V = nRT

R = 8.314; M = molarity

Homework

Page 567: 61, 69, 73, 75, 77