Compounds in Aqueous
Solutions
I. Dissociation
• Separation of ions that occurs when an
ionic compound dissolves in water
• Balance chemical equation for charge as
well as for atoms.
• CaCl2(s) → Ca2+(aq) + 2 Cl-(aq)
• Assume 100% dissociation – 1 mol of
calcium chloride produces one mol of
calcium ions and 2moles of chloride ions –
3 moles of ions total
II. Practice problems
• Write the equation for the dissociation of
each of the following in water, and then
determine the # of moles of each ion
produced as well as the total number of
moles of ions produced.
• A. 1 mol ammonium chloride
• B. 1 mol sodium sulfide
• C. 0.5 mol barium nitrate
III. Precipitation reactions
A. Solubility rules
B. Would the following be soluble? Which
rule?
• (NH4)2S(s) → 2NH4+ (aq) + S2-(aq)
• Cd(NO3)2 (s) →
C. When something is soluble it remains in
solution(aq). If it is not soluble, it
precipitates(s) out of solution.
IV. Net Ionic Equations
•
•
Reactions of ions in aqueous solutions
Only includes compounds and ions that undergo a
chemical change in a reaction in an aqueous solution.
1. Write overall equation
2. Write formula equation (Is each product
soluble or not)
3. Write overall ionic equation -Dissociate soluble
compounds into ions. Precipitates are shown
as solids.
4. Cancel out spectator ions. Do not undergo
any chemical change and do not take part in
the reaction. Found in solution before and
after reaction.
5. Write net ionic equation.
IV. Net Ionic Equations
1. Will a precipitate form when solutions of
ammonium sulfide and cadmium nitrate are
combined? Write net ionic equation.
Step 1 (NH4)2S + Cd(NO3)2 →
2NH4NO3+ CdS
Step 2 (NH4)2S(aq) + Cd(NO3)2(aq) →
2NH4NO3(aq) + CdS(s)
Ammonium nitrate is soluble – Rule #1,2
Cadmium sulfide is not soluble – precipitate –
Rule #5
Precipitation of cadmium sulfide
Step #3 Cd2+(aq) +2NO3-(aq) + 2NH4+(aq) + S2(aq) →CdS(s) + 2NO3-(aq) + 2NH4+(aq)
Step #4 Cd2+(aq) +2NO3-(aq) + 2NH4+(aq) + S2(aq) →CdS(s) + 2NO3-(aq) + 2NH4+(aq)
Step #5 Cd2+(aq) + S2-(aq) →CdS(s)
V. Practice problems
Problem #2 Will a precipitate form when
aqueous solutions of zinc nitrate and
ammonium sulfide are combined?
1. Equation for double replacement
2. Formula equation (includes state of
products)
3. Overall ionic equation
4. Net ionic equation – cancel out spectator
ions.
V. Practice problems
3. Will a precipitate form if solutions of
potassium sulfate and barium nitrate are
combined? If so, write the net ionic
equation for the reaction.
4. Will a precipitate form if solutions of
potassium nitrate and magnesium sulfate
are combined? If so, write the net ionic
equation for the reaction.