Ch. 13 Precipitation ReactionsCh. 13 Precipitation Reactions

Reactions in SolutionsReactions in Solutions

Precipitation ReactionsPrecipitation Reactions How do you know if a precipitate How do you know if a precipitate

will form when you mix two will form when you mix two solutions?solutions?

You look at the solubility of the You look at the solubility of the products.products.

Certain ionic compounds dissolve Certain ionic compounds dissolve in water, other ones do not.in water, other ones do not.

Soluble: means it dissolves in Soluble: means it dissolves in waterwater

Insoluble: means it makes a Insoluble: means it makes a precipitate (a solid) and the precipitate (a solid) and the solution will get cloudy.solution will get cloudy.

Soluble or Insoluble?Soluble or Insoluble?

The 3 Most Important The 3 Most Important Solubility Rules:Solubility Rules:

1. All Nitrates, NO1. All Nitrates, NO33-- , are soluble (always true). , are soluble (always true).

ie: KNOie: KNO33, Ca(NO, Ca(NO33))22, etc., etc. 2. Na, K, and NH2. Na, K, and NH44

++ compounds are soluble compounds are soluble ie: NHie: NH44Cl, KCl, K22SOSO44, etc., etc.

3. Compounds with Pb, Ag, and Hg tend not to 3. Compounds with Pb, Ag, and Hg tend not to be soluble. (PbSObe soluble. (PbSO44, Ag, Ag33POPO44, etc) , etc)

But:But: these these areare soluble with nitrates, for example, soluble with nitrates, for example, PbNOPbNO33 isis soluble. soluble.

This is just a broad overview. See Pg. 437 for This is just a broad overview. See Pg. 437 for specifics.specifics.

Solubility RulesSolubility Rules

Example:Example:

You mix silver nitrate and calcium chloride, You mix silver nitrate and calcium chloride, what happens?what happens?

2AgNO2AgNO3(aq)3(aq) + CaCl + CaCl2(aq) 2(aq) 2AgCl 2AgCl(s) (s) + Ca(NO+ Ca(NO33))2(aq)2(aq)

But only include the ions which “participate.”But only include the ions which “participate.” AgAg+ +

(aq)(aq) + Cl + Cl--(aq) (aq) AgCl AgCl(s)(s)

This is the “Net ionic equation.”This is the “Net ionic equation.” The other ions are called “spectator ions.”The other ions are called “spectator ions.” They are present before and after the reaction.They are present before and after the reaction.

Sample Problem:Sample Problem:

Write the net ionic equation for the Write the net ionic equation for the reaction which occurs when solutions of reaction which occurs when solutions of lead(II) nitrate and sodium bromide are lead(II) nitrate and sodium bromide are mixed.mixed.

Pb(NOPb(NO33))2(aq)2(aq) + 2NaBr + 2NaBr(aq) (aq) PbBr PbBr2(s) 2(s) + 2NaNO+ 2NaNO3(aq)3(aq)

And the “net ionic” equation:And the “net ionic” equation:PbPb2+2+ + 2Br + 2Br1-1- PbBr PbBr2(s)2(s)

The hazards of Ice Fishing….

Try this one:Try this one:

Copper(II)sulfate solution is mixed with Copper(II)sulfate solution is mixed with sodium phosphate.sodium phosphate.

Write the overall reaction first, then write the Write the overall reaction first, then write the “net ionic” equation.“net ionic” equation.

3CuSO3CuSO44 + 2Na + 2Na33POPO44 Cu Cu33(PO(PO44))2(s)2(s) + 3Na + 3Na22SOSO44

Net ionic: 3CuNet ionic: 3Cu2+2+ + 2PO + 2PO443-3- Cu Cu33(PO(PO44))2(s)2(s)

Diluting already made solutions:Diluting already made solutions:

So far, we just talked about making So far, we just talked about making solutions from crystals and water.solutions from crystals and water.

How do you dilute an already made How do you dilute an already made solution to the molarity you want? solution to the molarity you want?

Use: Use: MMddVVdd = M = MccVVcc

““d” means “dilute d” means “dilute ““c” means concentrate.c” means concentrate.

Here’s a problem:Here’s a problem: How would you make 500 mL of 3.0 M How would you make 500 mL of 3.0 M

sulfuric acid from the stock solution, which is sulfuric acid from the stock solution, which is 17.8 M?17.8 M?

MMdd = 3.0 M M = 3.0 M Mc c = 17.8 M= 17.8 M

VVd d = 500 mL= 500 mL VVcc = ? = ?

To make it, get 84.2 mL of the concentrated acid To make it, get 84.2 mL of the concentrated acid from the bottle, add it to a volumetric flask, and from the bottle, add it to a volumetric flask, and add water until you reach the 500 mL line.add water until you reach the 500 mL line.

Conc. 84.2mLc

ddc M

VMV

Try this one:Try this one: What would be the Molarity of a solution you What would be the Molarity of a solution you

made by diluting 12.5 mL of 11.7 Molar HCl to made by diluting 12.5 mL of 11.7 Molar HCl to make 500. mL of solution?make 500. mL of solution?

MMdd = ? = ? MMc c = 11.7 M= 11.7 M

VVd d = 500 mL= 500 mL VVcc = 12.5 mL = 12.5 mL

HCl 29.0 MV

VMM

d

ccd