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Concentration Units

moles of solute. liters of solution. moles of solute. m =. mass of solvent (kg). M =. Concentration Units. Molarity (M). Molality (m). 12.3. moles of solute. m = molality =. What is the molality of a solution prepared by dissolving 3.4 moles of KI into 500.g of water?.

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Concentration Units

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  1. moles of solute liters of solution moles of solute m = mass of solvent (kg) M = Concentration Units Molarity(M) Molality(m) 12.3

  2. moles of solute m =molality= What is the molality of a solution prepared by dissolving 3.4 moles of KI into 500.g of water? kg of solvent Molality The molal concentrationof a solution is expressed as the moles of solute per kilogramof solvent. 3.4 moles ------------ = 1.7 m .500 kg # of moles = 3.4 Mass of water = 500g or .500kg

  3. moles of solute m= mass of solvent (kg) What is the molality of a solution made from 155g of sodium chloride and 1500g of water? 155g of NaCl ---------------- = 2.65 molNaCl 58.5g/mol 1500g of water = 1.5kg of water 2.65 moles NaCl ____________________ =1.8m 1.5kg water

  4. Colligative Properties The addition of solutes into a solvent changes the physical properties of the solvent. Two examples of this would be boiling point elevation and freezing point depression.

  5. 12.6

  6. moles of solute m= mass of solvent (kg) 149 moles = 3.202 kg solvent What is the freezing point of a solution containing 149 moles of ethylene glycol (antifreeze) in 3202 g of water? DTf = Kfm Kf water = 1.86 0C/m = 2.41 m DTf = Kfm = 1.86 0C/m x 2.41 m = 4.48 0C = 0.00 0C – 4.48 0C = -4.48 0C Tf = T f – DTf

  7. actual number of particles in solution van’t Hoff factor (i) = number of formula units dissolved in the solution Colligative Properties of Electrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 0.1 mNaCl solution 0.1 m Na+ ions & 0.1 mCl- ions ivalue Example solute 1 nonelectrolytes 2 NaCl CaCl2 3 12.7

  8. Change in Freezing Point • Which chemical would be most effective to de-ice a frozen street and why? • SiO2 • NaCl • CaCl2

  9. Freezing Point Depression At what temperature will a 5.4 molal solution of NaCl freeze? Solution ∆Tfp= Kf • m • i ∆Tfp= (1.86 oC/molal) • 5.4 m • 2 ∆Tfp= 20.oC FP = 0 – 20. = -20. oC

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