Bellringer At the pizza party last night you and two friends decide to go to Mexico City from El Paso, TX where y'all live. You volunteer your car if everyone chips in for gas. Someone asks how much the gas will cost per person on a round trip. Your first step is to call your smarter brother to see if he'll figure it out for you. Naturally he's too busy to bother, but he does tell you that it is 2015 km to Mexico City, there's 11 cents to the peso, and gas costs 5.8 pesos per liter in Mexico. You know your car gets 21 miles to the gallon, but we still don't have a clue as to how much the trip is going to cost (in dollars) each person in gas ($/person).

IV. Solubility and Precipitation Reactions (Find Things to know!) Ch. 13 – Solutions

CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) A. Combustion the burning of any substance in O2 to produce heat A + O2  B CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

A + B  AB H2(g) + Cl2(g)  2 HCl(g) B. Synthesis the combination of 2 or more substances to form a compound only one product A + B  AB H2(g) + Cl2(g)  2 HCl(g)

AB  A + B 2 H2O(l)  2 H2(g) + O2(g) C. Decomposition a compound breaks down into 2 or more simpler substances only one reactant AB  A + B 2 H2O(l)  2 H2(g) + O2(g)

Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) D. Single Replacement one element replaces another in a compound metal replaces metal (+) nonmetal replaces nonmetal (-) A + BC  AC + B Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)

Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq) E. Double Replacement ions in two compounds “change partners” cation of one compound combines with anion of the other AB + CD  AD + CB Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)

F. Precipitation Reactions What does this mean: PbCrO4(s) ? Sometimes when 2 aqueous solutions are mixed a solid is produced. This insoluble solid is called a precipitate, and the reaction is known as a precipitation reaction.

F. Precipitation Reactions ZnBr2 (aq) + 2 AgNO3 (aq) → Zn(NO3)2 + 2 AgBr (aq) means the compound is present as ions. ZnBr2 (aq) Zn2+(aq) + 2 Br-(aq) AgNO3 (aq) Ag+(aq) + NO3-(aq) Also known as Dissociation Equations

F. Precipitation Reactions We can rewrite our equation as: Zn2+(aq) + 2 Br-(aq) + 2 Ag+(aq) + 2 NO3-(aq)     Zn2+(aq) + 2 NO3-(aq)+ 2 AgBr(s)

F. Precipitation Reactions Spectator ions: Ions that are present in a reaction but do not participate The same on both the reactant and product side of the equation so they are “cancelled out”.

F. Precipitation Reactions Reactions in which the spectator ions have been removed are called net ionic equations. 2 Ag+(aq) + 2 Br-(aq) → 2 AgBr(s) A net ionic equation shows only the ions involved in the formation of the precipitate or solid, (s).

F. Precipitation Reactions Example: Mg(CH3COO)2 + (NH4)2SO4 ? Predict the products Write a balanced equation Refer to a table of solubility to determine whether either, or both, of the two products will form insoluble precipitates.

F. Precipitation Reactions We find that both MgSO4 and NH4CH3COO are soluble compounds, meaning they will remain in solution and not form precipitates. Thus, there is really NO REACTION occurring, since all ions simply remain in solution!