Ch 18 Notes IIPrecipitation Reactions

Solubility Rules• The solubility rules will tell you if

a compound will be soluble in water.

• Note, this does not tell us how soluble it is, just whether or not it will dissolve.

Soluble or Insoluble?NaNO3

KClO4

PbBr2

K2CrO4

Ca(OH)2

Fe2S3

AgClNa3PO4

Hg2SO4

Fe(CN)3

Ba(C2H3O2)2

SrS

Precipitation• Precipitation is the formation of a

solid in a solution during a chemical reaction.

• The precipitate is the solid formed due to creation of an insoluble compound.

• The remaining liquid is called the supernatant.

• Lead (II) nitrate and potassium iodide solutions are mixed together. The yellow stuff is a solid, insoluble

compound. What could it be?

• The positive lead ion could go with the negative iodide ion and the positive potassium ion could go with the negative nitrate ion. Are either of the resulting compounds insoluble?

• PbI2 is insoluble, KNO3 is not, so we say lead (II) iodide precipitates!

What precipitate forms between:• Barium nitrate and sodium sulfate• Potassium chloride and silver acetate

• Ca(ClO3)2 and (NH4)2CrO4

• KClO4 and Li2Cr2O7

• FeCl3 and Ba(OH)2

Net Ionic Equations• We have already seen that when an

ionic compound dissolves, it is broken into its positive and negative ions.

Net Ionic Equations• A net ionic equation shows how the

ions in a solution react together, instead of the entire compounds, ignoring ions that do not react.

• Ions that do not undergo reaction, but stay in solution are called spectator ions.

NOTE: The following slide is a simplification—we will revisit this later!

Write the net ionic equation for the reaction:• Write the ions that could react.• Write insoluble products together as a

compound and soluble products as ions.

• Cancel any ions on both sides. Insoluble compounds are marked with an (s) for solid.

Solutions of potassium chromate and silver nitrate are combined.

Write the reactants as ions

K+ + CrO42- + Ag+ + NO3

- Determine the productsK+ +CrO4

2- +Ag+ + NO3-K+ + NO3

- +Ag2CrO4(s)

Cross out ions that don’t changeK+ +CrO4

2- +Ag+ + NO3-K+ + NO3

- +Ag2CrO4(s)

Ag+ +CrO42- Ag2CrO4(s)

Balance by adding coefficients to the ions as needed.

2Ag+ +CrO42- Ag2CrO4(s)

Solutions of potassium chromate and silver nitrate are combined.

Write the net ionic equation for combination of solutions of:

• Calcium chlorate and sodium phosphate

• Sodium bromide and silver acetate

• (NH4)2S and Al(NO3)3