Concentration …a measure of solute-to-solvent ratio concentrated vs. dilute

1. Concentration…a measure of solute-to-solvent ratio concentrated vs. dilute “lots of solute” “not much solute” “watery” Add water to dilute a solution; boil water off to concentrate it.

2. How to prepare 500 mL of 1.54 M NaCl solution Preparing Solutions • mass 45.0 g of NaCl • add water until total volume is 500 mL 500 mL volumetric flask 500 mL mark 45.0 g NaCl solute

3. mass of solvent only 1 kg water = 1 L water Molality

4. 500 mL of 1.54M NaCl Preparing Solutions molarity molality 1.54m NaCl in 0.500 kg of water • mass 45.0 g of NaCl • add water until total volume is 500 mL • mass 45.0 g of NaCl • add 0.500 kg of water 500 mLwater 500 mL volumetric flask 500 mL mark 45.0 gNaCl

5. occurs when neutral combinations of particles separate into ions while in aqueous solution. Dissociation NaCl Na1+ + Cl1– sodium chloride sodium hydroxide NaOH Na1+ + OH1– hydrochloric acid HCl H1+ + Cl1– sulfuric acid H2SO4 2 H1+ + SO42– CH3COOH CH3COO1– + H1+ acetic acid ? In general, acids yield hydrogen ions (H1+) ? in aqueous solution; bases yield hydroxide ions. (OH1–)

6. Dissociate in Water

7. NaCl Na1+ + Cl1– CH3COOH CH3COO1– + H1+ Strong electrolytes exhibit nearly 100% dissociation. NOT in water: 1000 0 0 in aq. solution: 1 999 999 Weak electrolytes exhibit little dissociation. NOT in water: 1000 0 0 in aq. solution: 980 20 20 “Strong” or “weak” is a property of the substance. We can’t change one into the other.

8. Formation of a solid AgCl AgNO3(aq) + KCl(aq)  KNO3 (aq) + AgCl(s) Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 220

9. Colligative Propertiesdepend on concentration of a solution Compared to solvent’s… a solution w/that solvent has a… …normal freezing point (NFP) …lower FP FREEZING PT. DEPRESSION …normal boiling point (NBP) …higher BP BOILING PT. ELEVATION

10. Applications (NOTE: Data are fictitious.) Effect of Pressure on Boiling Point 1. salting roads in winter water + a little salt –11oC 103oC water + more salt –18oC 105oC 2. antifreeze (AF) /coolant

11. Freezing Point Depression Boiling Point Elevation DTf = Kf m i DTb = Kb m i Then use these in conjunction with the NFP and NBP to find the FP and BP of the mixture.

12. Calculations for Colligative Properties The change in FP or BP is found using… DTx = Kx m i DTx = change in To (below NFP or above NBP) Kx = constant depending on… (A) solvent (B) freezing or boiling m = molality of solute = mol solute / kg solvent i = integer that accounts for any solute dissociation any sugar (all nonelectrolytes)……………...i = 1 table salt, NaCl  Na1+ + Cl1–………………i = 2 barium bromide, BaBr2  Ba2+ + 2 Br1–……i = 3

13. Pressure here Reverse Osmosis Water Solution Semipermeable membrane Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 267

14. semipermeable membrane Net Solvent Flow Dilute solution Net flow of solvent Net flow of solvent Concentrated solution Solute particle Solvent particle Ralph A. Burns, Fundamentals of Chemistry 1999, page 430