Unit 2 - Chemical Reactions

Double displacement

• occurs between ions in aqueous solution. A reaction will occur when a pair of ions come together to produce at least one of the following: – a precipitate – a gas – water or some other non-ionized substance.

• Basic form: AX  +  BY  →    AY  +  BX

Example• Formation of precipitate.

– NaCl (aq) + AgNO3(aq)→ NaNO

3(aq)  + AgCl(s)

– BaCl2(aq) +Na

2SO

4(aq) →2NaCl(aq) +BaSO

4(s)

• Formation of a gas. – HCl(aq) + FeS(s) → FeCl

2(aq) +H

2S(g)

• Formation of water.• (If the reaction is between an acid and a base it is

called a neutralization reaction.) HCl(aq) + NaOH(aq)→ NaCl(aq) + H

2O(l)

• Formation of a product which decomposes.• CaCO

3(s) +HCl(aq)→ CaCl

2(aq) + CO

2(g)+H

2O(l)

PREDICTING PRECIPITATION REACTIONS USING

SOLUBILITY RULES• How do you determine the state of the

products?• Use the solubility rules to decide whether

a product of an ionic reaction is insoluble in water and will thus form a precipitate ( an insoluble compound formed during a chemical reaction in solution.) Use (S)

• If a compound is soluble in water then it should be shown as being in aqueous solution use (aq)

Examples:

If we add a solution of KCl to a AgNO3 solution will a precipitate form? We first write a predicted reaction.

KCl(aq) + AgNO3(aq) KNO3 + AgCl

Then we look at the solubility table to see if any of the products are insoluble in water.

We see that the table indicates that AgCl is insoluble - most chlorides are soluble except for Ag+, Hg2+, Hg2

2+ and Pb2+

The molecular equation then becomes:

KCl(aq) + AgNO3(aq) KNO3(aq)+ AgCl(s)

If we add a solution of NaNO3 to an NH4Cl solution will a precipitate form?The predicted equation then becomes: NaNO3(aq) + NH4Cl(aq) NaCl + NH4NO3

We see that the table indicates that both compounds are soluble - most chlorides are soluble, NaCl is soluble, and nitrates are soluble as well as NH4

+ compounds, so mixing these two solutions gives no precipitates, no reaction results. After the we would write N. R. for no reaction.

Practice• Use your solubility table to determine whether the

following compounds are soluble in water and indicate the state.

Ionic Compound Chemical formula Soluble/Insoluble? State

lead (II) sulfate

ammonium sulfide

silver nitrate

silver chloride

calcium carbonate

ammonium hydroxide

barium hydroxide

Examples

• Predict if a new product will form when a solution of sodium chloride is mixed with a solution of potassium bromide. Write the balanced chemical equation including states.

PracticeDetermine the products and write the balanced chemical reaction for the following.

Include the states for all reactants and products.

1. A solution of lead (II) nitrate mixed with a solution of sodium chloride.

2. A solution of sodium sulfate is mixed with a solution of calcium chloride

3. A solution of magnesium acetate mixed with a solution of silver nitrate.

4. A solution of strontium nitrate mixed with a solution of sodium sulfate.

5. A solution of barium nitrate mixed with ammonium phosphate.

IONIC EQUATIONSNet Ionic equations-only involve those chemical species which are involved in a chemical reaction. All spectator ions are eliminated.

Spectator ions-those ions which do not participate in the chemical reaction but are present in the reaction mixture

Write the molecular, ionic, and net ionic equations for the reaction of an aqueous solution of CaCl2 and an aqueous solution of Na2CO3.

1) the molecular equation is: CaCl2(aq) + Na2CO3(aq) CaCO3(s)+2NaCl(aq)

2) the ionic equation is: Ca2+

(aq) + 2 Cl-(aq) + 2 Na+

(aq) + CO32-

(aq)

CaCO3(s) + 2 Na+(aq) + 2 Cl-

(aq)

3) the net ionic equation is: Ca2+

(aq) + CO32- (aq) CaCO3(s)

molecular

ionic

net ionic