Adding a non-volatile (doesn’t readily evaporate) solute affects… • Conductivity (electrolytes) • Freezing point • Boiling point • Vapor pressure
Freezing Point Depression • Adding solute will lower the freezing point • Which one will lower the freezing point more? • NaCl or MgCl2 • Na+1 (aq) + Cl-1(aq) Mg+2 (aq) + 2Cl-1(aq) • 1 mol + 1 mol = 2 moles 1 mol + 2 mol = 3 moles
Vapor Pressure Decreased • Solute particles at the surface get in the way of some solvent molecules evaporating
Boiling Point Elevation • Adding solute will raise the boiling point • Which one will raise the boiling point more? • Sugar (C12H22O11) or salt (NaCl) • C12H22O11 (aq) Na+1 (aq) + Cl-1(aq) • 1 mol 1 mol + 1mol = 2 moles
Boiling Point Freezing Point Vapor Pressure
Depends on the # of moles dissolved in the solution and NOT on the type of particlesThe higher the concentration of solute in solvent, the more MP, BP, and VP are affect
Which solution containing 1 mole of solute dissolved in 1000 g of water has the lowest freezing point? • C2H5OH(aq) • NaCl(aq) • KOH(aq) 4) CaCl2(aq) Be careful! What if the question asked which solution has the highest freezing point?
C6H12O6 • Covalent • Dissolves as molecules C6H12O6(s) C6H12O6(aq) • 1 mole of sugar yields 1 mole of molecules
NaCl • Ionic • Dissolves as ions • NaCl(s) Na+(aq) + Cl-(aq) • 1 mole of salt yields 2 moles of ions. Get more particles from salt than sugar.
MgCl2 • Ionic • Dissolves as ions • MgCl2(s) Mg2+(aq) + 2Cl-(aq) • 1 mole of salt yields 3 moles of ions