Molality and Colligative Properties’ Objective: Calculate molality (m) Define colligative property Calculate changes in freezing and boiling point Terms Molality (m) Colligative property Boiling-point elevation Freezing-point depression Freezing-point depression constant Water = 1.86 Boiling-point elevation constant Water = 0.51

Molality (m) [LOWER CASE EHMM) Molality (m) is SIMILAR to (M) Molality = 𝑀𝑜𝑙𝑒𝑠 𝑆𝑜𝑙𝑢𝑡𝑒 (𝑃𝑜𝑤𝑑𝑒𝑟) 𝐾𝑔 𝑆𝑜𝑙𝑣𝑒𝑛𝑡 (𝑊𝑎𝑡𝑒𝑟) 1) Given 200 grams of NaCl and 400 mL of water calculate the molality of the solution. (you may assume that 1mL = 1 gram) (NaCl = 58.44 g/mol)

Colligative Property Boiling Point Elevation A colligative property is a characteristic or trait that DOES NOT depend on what the substance is, rather the colligative property depends on the quantity of the substance. Boiling point elevation = The boiling point increases as you dissolve more solute. It doesn’t really matter what the solute (powder) is… all that matters is how much you dissolve. Why does this happen?

Colligative Property Freezing Point Depression Freezing Point depression = Freezing point goes down as you dissolve more solute… why? Both Freezing Point depression and boiling point elevation can be calculated by almost the same formula i = # of particles a substance generates (NaCl = 2) ΔBoiling Point = (i)(Kb )(m) Kb = BP Elevation constant M = molality