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 only Unsaturated – a solution that may dissolve more solute Supersaturated – 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 10 6 g of solution Ppm = mass of component x 10 6 total mass Example units – 1mg/kg or 1 mg/L

PPB – parts per billion Similar to above but... billion (10 9 ) 1 ppb = 1 g per 10 9 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

M olality m = moles of solute kg of solvent units – mol/kg or m *** Be careful lots of M’s

Example Calculate the mass percent, ppm solute, and mole fraction of solvent for a solution of HC 2 H 3 O 2 that has a molality of mol solute 1 kg solvent 3.5 mole x 60 g = 210 g solute 1 mole Mass % = 210 g solute x 100 = 17.36% 1000 g g Ppm = 210g x 10 6 = ppm 1210 g 1000 g H 2 O x 1 mole = mole 18 g Mole fraction = mole =

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 P A = X A Pº A P A = partial pressure of A X A = Mole fraction of A Pº A = 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  T b = k b m  T b = change in temp K b = 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  T f = k f m  T f = change in temp K f = 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