Precipitation Reactions Precipitation reactions are reactions in which a solid forms when we mix two solutions reactions between aqueous solutions of ionic compounds produce an ionic compound that is insoluble in water the insoluble product is called a precipitate
2 KI(aq) + Pb(NO 3 ) 2 (aq) PbI 2 (s) + 2 KNO 3 (aq)
No Precipitate Formation = No Reaction KI(aq) + NaCl(aq) KCl(aq) + NaI(aq) all ions still present, no reaction
Process for Predicting the Products of a Precipitation Reaction 1. Determine what ions each aqueous reactant has 2. Determine formulas of possible products exchange ions (+) ion from one reactant with (-) ion from other balance charges of combined ions to get formula of each product 3. Determine solubility of each product in water use the solubility rules if product is insoluble or slightly soluble, it will precipitate 4. If neither product will precipitate, write no reaction after the arrow
Process for Predicting the Products of a Precipitation Reaction 5. If any of the possible products are insoluble, write their formulas as the products of the reaction using (s) after the formula to indicate solid. Write any soluble products with (aq) after the formula to indicate aqueous. 6. Balance the equation remember to only change coefficients, not subscripts
Example: Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(ii) chloride 1. Write the formulas of the reactants K 2 CO 3 (aq) + NiCl 2 (aq) 2. Determine the possible products a) determine the ions present b) exchange the Ions (K + + CO 3 ) + (Ni 2+ + Cl ) (K + + CO 3 ) + (Ni 2+ + Cl ) (K + + Cl ) + (Ni 2+ + CO 3 ) c) write the formulas of the products balance charges K 2 CO 3 (aq) + NiCl 2 (aq) KCl + NiCO 3
Example: Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(ii) chloride 3. Determine the solubility of each product KCl is soluble NiCO 3 is insoluble 4. If both products are soluble, write no reaction does not apply because NiCO 3 is insoluble
Example: Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(ii) chloride 5. Write (aq) next to soluble products and (s) next to insoluble products K 2 CO 3 (aq) + NiCl 2 (aq) KCl(aq) + NiCO 3 (s) 6. Balance the equation K 2 CO 3 (aq) + NiCl 2 (aq) 2 KCl(aq) + NiCO 3 (s)
Practice Predict the products and balance the equation KCl(aq) + AgNO 3 (aq) (K + + Cl ) + (Ag + + NO 3 ) (K + + NO 3 ) + (Ag + + Cl ) KCl(aq) + AgNO 3 (aq) KNO 3 + AgCl KCl(aq) + AgNO 3 (aq) KNO 3 (aq) + AgCl(s) Na 2 S(aq) + CaCl 2 (aq) (Na + + S ) + (Ca 2+ + Cl ) (Na + + Cl ) + (Ca 2+ + S ) Na 2 S(aq) + CaCl 2 (aq) NaCl + CaS Na 2 S(aq) + CaCl 2 (aq) NaCl(aq) + CaS(aq) No reaction
Practice Write an equation for the reaction that takes place when an aqueous solution of (NH 4 ) 2 SO 4 is mixed with an aqueous solution of Pb(C 2 H 3 O 2 ) 2. (NH 4 ) 2 SO 4 (aq) + Pb(C 2 H 3 O 2 ) 2 (aq) (NH 4 + + SO 4 ) + (Pb 2+ + C 2 H 3 O ) (NH 4 + + C 2 H 3 O ) + (Pb 2+ + SO 4 ) (NH 4 ) 2 SO 4 (aq) + Pb(C 2 H 3 O 2 ) 2 (aq) NH 4 C 2 H 3 O 2 + PbSO 4 (NH 4 ) 2 SO 4 (aq) + Pb(C 2 H 3 O 2 ) 2 (aq) NH 4 C 2 H 3 O 2 (aq) + PbSO 4 (s) (NH 4 ) 2 SO 4 (aq) + Pb(C 2 H 3 O 2 ) 2 (aq) 2 NH 4 C 2 H 3 O 2 (aq) + PbSO 4 (s)
Ionic Equations Equations that describe the chemicals put into the water and the product molecules are called molecular equations 2 KOH(aq) + Mg(NO 3 ) 2 (aq) 2 KNO 3 (aq) + Mg(OH) 2 (s) Equations that describe the material s structure when dissolved are called complete ionic equations aqueous strong electrolytes are written as ions soluble salts, strong acids, strong bases insoluble substances, weak electrolytes, and nonelectrolytes are written in molecule form solids, liquids, and gases are not dissolved, therefore molecule form 2K + (aq) + 2OH (aq) + Mg 2+ (aq) + 2NO 3 (aq) 2K + (aq) + 2NO 3 (aq) + Mg(OH) 2(s)
Ionic Equations Ions that are both reactants and products are called spectator ions 2 K + (aq) + 2 OH (aq) + Mg 2+ (aq) + 2 NO 3 (aq) 2 K + (aq) + 2 NO 3 (aq) + Mg(OH) 2(s) An ionic equation in which the spectator ions are removed is called a net ionic equation 2 OH (aq) + Mg 2+ (aq) Mg(OH) 2(s)
Practice Write the ionic and net ionic equation for each K 2 SO 4 (aq) + 2 AgNO 3 (aq) 2 KNO 3 (aq) + Ag 2 SO 4 (s) 2K + (aq) + SO 4 (aq) + 2Ag + (aq) + 2NO 3 (aq) 2K + (aq) + 2NO 3 (aq) + Ag 2 SO 4 (s) 2 Ag + (aq) + SO 4 (aq) Ag 2 SO 4 (s) Na 2 CO 3 (aq) + 2 HCl(aq) 2 NaCl(aq) + CO 2 (g) + H 2 O(l) 2Na + (aq) + CO 3 (aq) + 2H + (aq) + 2Cl (aq) 2Na + (aq) + 2Cl (aq) + CO 2 (g) + H 2 O(l) CO 3 (aq) + 2 H + (aq) CO 2 (g) + H 2 O(l)