1. Chapter 13 Solutions

2. Solution = Solvent + Solute
Solution – a homogenous mixture of two or more substances or components, with the major component being the solvent and the other minor components being solutes
Solvent - a substance that dissolves another substance
Or, the substance present in greater amount
Solute - a substance which is dissolved by another substance
Or, the substance present in lesser amount

3. Colligative properties
A property that depends on the amount of a particles in a solution
Independent of type of particle
Ions, atoms, molecules
Electrolytes generate multiple particles when dissolved

4. Practice Assuming complete ionization upon dissolution
1 mole Na2CO3 = ? moles of ions
2 moles of CaCl2 = ? moles of ions
3 moles of Fe3(PO4)2 = ? moles of ions
Practice

5. Colligative properties and nonelectrolytes
1 mole of non volatile nonelectrolyte will form 1 mole of dissolved particles
Sugars, ethylene glycol
Vapor pressure lowering
Freezing point depression
Boiling point elevation
Osmotic pressure
Colligative properties and nonelectrolytes

6. Vapor pressure lowering
A solution will have a lower vapor pressure than the pure solvent
Dissolved particles reduce vaporization rate, creating a new equilibrium that favors more molecules in the liquid phase instead of gas phase
Less gas molecules = lower vapor pressure

7. Raoult’s law
The vapor pressure of the solution is dependent on the moles of solute per mole of solvent
𝑃 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 = χ 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 𝑃 𝑠𝑜𝑙𝑣𝑒𝑛𝑡
Also the difference in vapor pressure between the solution and the pure solvent is
∆𝑃= χ 𝑠𝑜𝑙𝑢𝑡𝑒 𝑃 𝑠𝑜𝑙𝑣𝑒𝑛𝑡

8. Calculate the vapor pressure at 25°C of a solution containing 99
Calculate the vapor pressure at 25°C of a solution containing 99.5g sucrose (C12H22O11) and 300 g of water. The vapor pressure of pure water at 25°C is torr.
Practice

9. Vapor pressure and volatile solutes
Vapor pressure of solute contributes to total vapor pressure of solution
Applies for an ideal solution – solute- solvent interactions are similar to the solute-solute and solvent-solvent interactions
𝑃 𝑇𝑜𝑡 = 𝑃 𝐴 + 𝑃 𝐵

10. Deviations from Raoult’s law
In an nonideal solution solute-solvent interactions can be stronger or weaker than solute-solute or solvent-solvent interactions

11. Freezing point depression
Dissolved particles will depress (lower) the freezing point of a solvent
∆ 𝑇 𝑓 =m× 𝐾 𝑓
m = molality = moles of solute per kilogram of solvent
Kf = freezing point depression constant for the solvent
For water Kf = 1.86°C/m

12. Boiling point elevation
Dissolved particles will elevate (raise) the boiling point of a solvent
∆ 𝑇 𝑏 =m× 𝐾 𝑏
m = molality = moles of solute per kilogram of solvent
Kb = boiling point elevation constant for the solvent
For water Kb = 0.512°C/m

13. Phase diagram: solution vs pure solvent

14. Osmotic pressure
Osmosis – the flow of solvent, through a semipermeable membrane, going from regions of lower solute concentration to a region of higher solute concentration
Osmotic pressure – the pressure required to stop the osmotic flow

15. Π=M𝑅𝑇 Osmotic pressure Π = osmotic pressure M = molarity (moles/Liter)
R = ideal gas constant (pressure*Liter/moles*Kelvin)
T = Temperature (Kelvin)

16. Colligative properties for strong electrolyte solutions
In reality, strong electrolytes do not completely dissociate
Ions can pair up, decreasing the amount of total dissolved particles than would be expected
Van’t Hoff factor (i) – the ratio of moles of particles in solution to the moles of formula units dissolved
𝑖= moles of particles moles of formula units dissolved

17. Strong electrolyte incorporation
∆ 𝑇 𝑓 =im× 𝐾 𝑓
∆ 𝑇 𝑏 =im× 𝐾 𝑏
Π=iM𝑅𝑇

18. The end