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Chapter 5

Chemical Reactions

Dissolution of (a) Ionic and(b) Molecular Compounds

Electrolytes

• All salts are strong electrolytes, that is they dissociate into ions in solution

• If they are significantly soluble then the dissolved ions make the solution a good conductor of electricity

• Molecular compounds except for acids and bases are non-electrolytes, non-conductors

Solubility Rules

1. All group I and ammonium salts are soluble (this rule holds above all others)

2. All nitrates and acetates are soluble

3. Phosphates and carbonates are generally insoluble (note rule 1)

4. Most sulfides and hydroxides are insoluble (note rule 1)

Ca2+, Sr2+, Ba2+ sulfides and hydroxides are soluble

5. Most sulfates are soluble

Ba2+, Sr2+, Hg22+, Pb2+ sulfates are insoluble

6. Most halides (Cl–, Br–, I–) are soluble

Ag+, Hg22+, Pb2+ halides are insoluble

Exceptions in red may show up on exams

Illustration of Some

Solubility Rules

Which of the following salts is insoluble in water

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Na2S

(NH4)3PO4

Ag2SO4

Ba(OH)2

AgI

0% 0% 0%0%0%

1. Na2S

2. (NH4)3PO4

3. Ag2SO4

4. Ba(OH)2

5. AgI

0

0

130

Precipitation Reactions

If either of the possible products of a double replacement are in soluble then a precipitate will form. A chemical reaction occurs.

If both possible products are soluble there is no reaction.

Precipitation of Silver Chloride

AgNO3 + NaCl AgCl + NaNO3

precipitate

Mixing which of the following pairs of solutions will result in formation

of a precipitate?

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0% 0% 0%0%0%

1. NaCl and Ba(NO3)2

2. K2SO4 and Ba(C2H3O2)2

3. FeSO4 and KI

4. NaBr and Cr(NO3)3

5. MgSO4 and CuCl2

0

0

130

Writing equations for Precipitation Reactions

• Swap partners – Na2SO4 + Fe3(PO4)2

• Check solubility rules – Fe3(PO4)2 is insoluble

• Write unbalanced equation –Na3PO4(aq)+FeSO4(aq)Na2SO4(aq)+Fe3(PO4)2(s)

• Balance –2Na3PO4(aq)+3FeSO4(aq)3Na2SO4(aq)+Fe3(PO4)2(s)

Na3PO4 + FeSO4

Ionic Equations• Write the balanced equation of reaction2Na3PO4(aq)+3FeSO4(aq)3Na2SO4(aq)+Fe3(PO4)2(s)

• Total Ionic Equation – Separate all aqueous strong electrolytes into ions:

6Na+(aq) + 2PO43-(aq) + 3Fe2+(aq) + 3SO4

2-(aq) 6Na+(aq) + 3SO4

2-(aq) + Fe3(PO4)2(s)

• Net Ionic Equation – Eliminate spectator ions2PO4

3-(aq) + 3Fe2+(aq) Fe3(PO4)2(s)

Acids

• substances that donates H+ ions to solution

• sour-tasting substances

• substances whose aqueous solutions are capable of turning blue litmus indicators red

• dissolves certain metals to form salts

• react with bases or alkalis to form salts

Bases

• substances that donates a OH- ion to solution

• hydroxides and oxides of metals

• bitter tasting, slippery solutions

• turn litmus blue

• react with acids to form salts

Ionization of Acids in Water

Strong electrolyteWeak electrolyte

Common Acids and Bases

Learn

All othersare weak

Neutralization Reactions

acid + base “salt” + water

HCl + NaOH NaCl + H2O

H2SO4 + 2KOH K2SO4 + 2H2O

Strong vs. Weak Acids and Bases

• strong – completely ionized– separate into ions in ionic equation

• weak – partially ionized– keep intact in ionic equation

Ionic Equations

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

Total Ionic Equation:H+ + Cl- + Na+ + OH- Na+ +Cl- + H2O

Net Ionic Equation:H+(aq) + OH-(aq) H2O(l)

Ionic Equations

H3PO4(aq) + 3KOH(aq) K3PO4(aq) + 3H2O(l)

Total Ionic Equation:H3PO4 + 3K+ + 3OH- 3K+ + PO4

3- + 3H2O

Net Ionic Equation:H3PO4(aq) + 3OH-(aq) PO4

3-(aq) + 3H2O(l)

What is the net ionic equation for the reaction of acetic acid with NaOH?

100

0

1300% 0%0%0%

1. H++OH-H2O

2. H++NaOHH2O+Na+

3. CH3COOH+OH-

CH3COO-+H2O

4. Na++ CH3COO-

NaCH3COO

Gas-Forming

Exchange Reaction

Reaction of Metal Carbonates with Acids

CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2CO3(aq)

H2CO3(aq) H2O + CO2(g)

Carbonic acid is unstable and releases carbon dioxide gas

Total Ionic Equation:CaCO3(s) + 2H+ + 2Cl- Ca2+ + 2Cl- + H2O + CO2(g)

Net Ionic Equation:CaCO3(s) + 2H+

(aq) Ca2+(aq) + H2O(l) + CO2(g)

Reaction of Metal Sulfites and Sulfides with Acids

CaSO3(s) + 2HCl(aq) CaCl2(aq) + H2SO3(aq)

H2SO3(aq) H2O + SO2(g)

Net Ionic Equation:

CaSO3(s) + 2H+(aq) Ca2+

(aq) + H2O(l) + SO2(g)

Na2S(aq) + 2HCl(aq) 2NaCl(aq) + H2S(g)

Net Ionic Equation:

S2-(aq) + 2H+

(aq) H2S(g)

Which of the following is a gas forming reaction?

100

0

130 0% 0%0%0%

1. Na2CO3+Ba(OH)2

2. AgNO3+Na2S

3. ZnCO3+HNO3

4. HCl+CuSO4