Chemistry: Solubility Rules and Precipitation Reactions
Predicting precipitates and writing ionic equations
Chemistry: Solubility Rules and Precipitation Reactions
Predicting precipitates and writing ionic equations
Chemistry - Grade 9-12
- 1
Classify each compound as soluble or insoluble in water: NaCl, AgCl, KNO3, BaSO4, and NH4Br.
Start with the rules for Group 1 ions, ammonium ions, and nitrate ions.
NaCl is soluble because most sodium salts are soluble. AgCl is insoluble because most chlorides are soluble except those with silver, lead(II), and mercury(I). KNO3 is soluble because all nitrates are soluble. BaSO4 is insoluble because most sulfates are soluble except those with barium, lead(II), strontium, and calcium. NH4Br is soluble because all ammonium salts are soluble. - 2
Predict whether a precipitate forms when aqueous solutions of silver nitrate and sodium chloride are mixed. Write the balanced molecular equation.
A precipitate forms because silver chloride is insoluble in water. The balanced molecular equation is AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq). - 3
Write the complete ionic equation for the reaction between AgNO3(aq) and NaCl(aq).
Separate strong aqueous electrolytes into ions, but do not split a solid precipitate into ions.
The complete ionic equation is Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) -> AgCl(s) + Na+(aq) + NO3-(aq). Sodium ions and nitrate ions remain dissolved as spectator ions. - 4
Write the net ionic equation for the reaction between AgNO3(aq) and NaCl(aq).
The net ionic equation is Ag+(aq) + Cl-(aq) -> AgCl(s). This shows only the ions that form the insoluble precipitate. - 5
Predict whether a precipitate forms when aqueous potassium sulfate and barium nitrate are mixed. If a precipitate forms, identify it.
Most sulfates are soluble, but barium sulfate is an important exception.
A precipitate forms because barium sulfate is insoluble in water. The precipitate is BaSO4(s), and potassium nitrate remains dissolved. - 6
Write the balanced molecular equation for the reaction between K2SO4(aq) and Ba(NO3)2(aq). Include states of matter.
The balanced molecular equation is K2SO4(aq) + Ba(NO3)2(aq) -> BaSO4(s) + 2KNO3(aq). The solid product is barium sulfate. - 7
A student mixes Pb(NO3)2(aq) and KI(aq). Predict the products, identify any precipitate, and write the balanced molecular equation.
Use double replacement to exchange the cations, then apply solubility rules to the products.
The products are PbI2 and KNO3. Lead(II) iodide is insoluble, so it forms a precipitate. The balanced molecular equation is Pb(NO3)2(aq) + 2KI(aq) -> PbI2(s) + 2KNO3(aq). - 8
Write the net ionic equation for the reaction between Pb(NO3)2(aq) and KI(aq).
The net ionic equation is Pb2+(aq) + 2I-(aq) -> PbI2(s). Potassium ions and nitrate ions are spectator ions. - 9
Will a precipitation reaction occur when NaNO3(aq) and KCl(aq) are mixed? Explain your answer.
A reaction is recorded as no reaction if all possible products remain aqueous.
No precipitation reaction occurs. The possible products are NaCl and KNO3, and both are soluble in water because Group 1 salts and nitrate salts are soluble. - 10
Complete and balance the molecular equation if a reaction occurs: CaCl2(aq) + Na2CO3(aq) ->
A reaction occurs because calcium carbonate is insoluble. The balanced molecular equation is CaCl2(aq) + Na2CO3(aq) -> CaCO3(s) + 2NaCl(aq). - 11
Write the complete ionic equation and the net ionic equation for CaCl2(aq) + Na2CO3(aq) -> CaCO3(s) + 2NaCl(aq).
Cancel the ions that appear unchanged on both sides of the complete ionic equation.
The complete ionic equation is Ca2+(aq) + 2Cl-(aq) + 2Na+(aq) + CO3 2-(aq) -> CaCO3(s) + 2Na+(aq) + 2Cl-(aq). The net ionic equation is Ca2+(aq) + CO3 2-(aq) -> CaCO3(s). Sodium ions and chloride ions are spectator ions. - 12
A solution contains Mg2+(aq), Na+(aq), Cl-(aq), and NO3-(aq). A few drops of NaOH(aq) are added. Predict whether a precipitate forms and write the net ionic equation.
A precipitate forms because magnesium hydroxide is insoluble. The net ionic equation is Mg2+(aq) + 2OH-(aq) -> Mg(OH)2(s). - 13
Use solubility rules to decide which ion pair will form an insoluble compound: Na+ and NO3-, Ag+ and Cl-, K+ and Br-, or NH4+ and SO4 2-. Explain your choice.
Look for exceptions to the rule that most chloride, bromide, and iodide salts are soluble.
Ag+ and Cl- will form an insoluble compound because silver chloride is insoluble. The other ion pairs form soluble compounds because nitrate salts, Group 1 salts, and ammonium salts are soluble. - 14
A chemist mixes equal volumes of 0.10 M FeCl3(aq) and 0.30 M NaOH(aq). Predict the precipitate and write the balanced molecular equation.
The precipitate is iron(III) hydroxide, Fe(OH)3(s), because most hydroxides are insoluble except those with Group 1 ions and some Group 2 ions. The balanced molecular equation is FeCl3(aq) + 3NaOH(aq) -> Fe(OH)3(s) + 3NaCl(aq). - 15
A reaction is represented by the net ionic equation Ba2+(aq) + SO4 2-(aq) -> BaSO4(s). Name two pairs of aqueous reactants that could produce this precipitate.
Choose soluble salts that provide Ba2+ ions and SO4 2- ions.
One possible pair is BaCl2(aq) and Na2SO4(aq). Another possible pair is Ba(NO3)2(aq) and K2SO4(aq). In both cases, the barium ions and sulfate ions combine to form insoluble BaSO4(s), while the other ions remain in solution.