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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