Lecture 72/4/05 Seminar: Monday 2/7 4:30 Room 006 Eric Howe “Untangling sickle-cell anemia and the discovery of heterozygote protection to address students’ misconceptions in genetics”

Quiz 3 1. Given the following reaction, NH 4 HS (s) ↔ NH 3 (g) + H 2 S (g)  H = + which direction will the reaction shift if you: a. Add more NH 4 HS b. Remove NH 3 c. Decrease the temperature 2. Give the balanced net ionic equation for the following reaction. Pb(NO 3 ) 2 + NaCl  Pb(Cl) 2 + NaNO 3

Le Chatelier’s review Given the following reaction: NH 4 HS (s) ↔ NH 3 (g) + H 2 S (g)  H = + which direction will the reaction shift if you: a. Add more NH 4 HS b. Remove NH 3 c. Decrease the temperature Q = [NH 3 ][H 2 S] At equilibrium, Q = K so reaction shifts only if you change Q a. Doesn’t change Q, so no change to reaction b. Q becomes smaller  Q < K  rxn shifts to right c. Q stays the same, but K gets smaller  Q > K  shifts left a. Still easier to think of heat as reactant, remove reactant so shift left

Q vs. K sp AgBr (s) ↔ Ag + (aq) + Br - (aq) Q = K sp Solution saturated with ions and is equilibrium Q < K sp Solution is unsaturated No precipitate forms Q > K sp Solution is oversaturated Precipitate forms

A chemistry student mixes 20.0 mL of 4.5 x M AgNO 3 with 10.0 mL of 7.5 x M of NaBrO 3. Will a precipitate of AgBrO 3 form? K sp (AgBrO 3 ) = 6.7 x Q > K, so will precipitate until Q = K

K sp (AgCl) = 1.8 x If you have solution that is 1.0 x M Ag +, what is the minimum Cl - concentration for a precipitate to form?