1. Chemical Reactions 9.3: Reactions in Aqueous Solutions

2. Objectives Describe aqueous solutions. Describe aqueous solutions. Write complete ionic and net ionic equations for chemical reactions in aqueous solutions. Write complete ionic and net ionic equations for chemical reactions in aqueous solutions. Predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas. Predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas.

3. A solution is a homogeneous mixture. Solutes are the substances that are dissolved. The solvent is the substance that does the dissolving. Water is the solvent in an aqueous solution. Review

4. Aqueous Solutions There can be many possible solutes in an aqueous solution: Ionic Compounds Dissolves Does not dissolve

5. Molecular Compounds

6. Review When an ionic compound dissolves in water, the ions in the compound will dissociate or separate from one another. (See previous slide). When an ionic compound dissolves in water, the ions in the compound will dissociate or separate from one another. (See previous slide). When the solute is a molecular compound, the molecules will not come apart; they will simply exist as separate molecules in solution. (See previous slide) When the solute is a molecular compound, the molecules will not come apart; they will simply exist as separate molecules in solution. (See previous slide) Recall that ionic compounds that produce hydrogen ions when in solution are called acids. Recall that ionic compounds that produce hydrogen ions when in solution are called acids.

7. Aqueous Solutions When two aqueous solutions of ionic compounds combine (both solutions then contain ions as solutes), the ions MAY react with one another. The solvent (water) molecules do not react. When two aqueous solutions of ionic compounds combine (both solutions then contain ions as solutes), the ions MAY react with one another. The solvent (water) molecules do not react. Recall that these reactions are double replacement reactions. Recall that these reactions are double replacement reactions. 3 types of products can form - a precipitate, water, or a gas. 3 types of products can form - a precipitate, water, or a gas.

8. Precipitate Reactions 2KI + Pb(NO 3 ) 2 2KNO 3 + PbI 2

9. The reaction in detail: K + NO 3 - I - NO 3 - Pb +2 KI and Pb(NO 3 ) 2 exist as IONS! PbI 2 (the precipitate) NO 3 - K + K+K+ I-I- K+K+ NO 3 -

10. Precipitate Reactions A chemical equation does not show what is really going on - we need to write an ionic equation to do that. A chemical equation does not show what is really going on - we need to write an ionic equation to do that. A complete ionic equation shows all the particles in a solution as they really exist. A complete ionic equation shows all the particles in a solution as they really exist. 2K + + 2I - + Pb +2 + 2NO 3 - PbI 2 (s) + 2K + + 2NO 3 - 2NO 3 -

11. Practice Problem The reaction above produces a solid copper compound. Write a balanced chemical equation and then a complete ionic equation.

12. Practice Problem The reaction above produces a solid copper compound. Write a balanced chemical equation and then a complete ionic equation. 1. Na 2 CO 3 + CuCl 2 CuCO 3 (s) + 2NaCl 2. 2Na + + CO 3 -2 + Cu +2 + 2Cl - CuCO 3 (s) + 2Na + + 2Cl -

13. Practice Problem A solution of silver nitrate and sodium chloride are mixed and a compound containing silver precipitates out. Write a balanced chemical equation and a complete ionic equation for this reaction.

14. Practice Problem A solution of silver nitrate and sodium chloride are mixed and a compound containing silver precipitates out. Write a balanced chemical equation and a complete ionic equation for this reaction. 1. AgNO 3 + NaCl AgCl (s) + NaNO 3 2. Ag + + NO 3 - + Na + + Cl - AgCl (s) + Na + + NO 3 -

15. Spectator ions Notice that on both sides of this reaction there are ions that do NOT participate in the reaction. These ions are called spectator ions.

16. Net Ionic Equations To write a net ionic equation, cross out all of the spectator ions. To write a net ionic equation, cross out all of the spectator ions. Ag + + Cl - AgCl (s) Ag + + Cl - AgCl (s) Practice: Practice: 2K + + 2I - + Pb +2 + 2NO 3 - PbI 2 + 2K + + 2K + + 2I - + Pb +2 + 2NO 3 - PbI 2 + 2K + + 2NO 3 2Na + + CO 3 -2 + Cu +2 + 2Cl - 2NO 3 2Na + + CO 3 -2 + Cu +2 + 2Cl - CuCO 3 (s) + 2Na + + 2Cl - CuCO 3 (s) + 2Na + + 2Cl -

17. More Practice! Write the chemical, complete ionic, and net ionic equations for the precipitate reactions below. Write the chemical, complete ionic, and net ionic equations for the precipitate reactions below. Solutions of barium nitrate and sodium carbonate are mixed, forming the precipitate barium carbonate. Solutions of barium nitrate and sodium carbonate are mixed, forming the precipitate barium carbonate. Solutions of aluminum chloride and sodium hydroxide are mixed, forming the precipitate aluminum hydroxide. Solutions of aluminum chloride and sodium hydroxide are mixed, forming the precipitate aluminum hydroxide.

18. Reactions that form Water Another type of double-replacement reaction that occurs in an aqueous solution produces water molecules. Another type of double-replacement reaction that occurs in an aqueous solution produces water molecules. Since water is colorless and odorless, there is no observable evidence that a reaction occurred. Since water is colorless and odorless, there is no observable evidence that a reaction occurred. HBr + NaOH NaBr + H 2 O HBr + NaOH NaBr + H 2 O H + + Br - + Na + + OH - Na + + Br - + H 2 O H + + Br - + Na + + OH - Na + + Br - + H 2 O H + + OH - H 2 O H + + OH - H 2 O

19. Practice Problems Write the chemical, complete ionic, and net ionic equations for the reactions below, which all produce water. Write the chemical, complete ionic, and net ionic equations for the reactions below, which all produce water. sulfuric acid and potassium hydroxide sulfuric acid and potassium hydroxide phosphoric acid and magnesium hydroxide phosphoric acid and magnesium hydroxide nitric acid and ammonium hydroxide nitric acid and ammonium hydroxide

20. Reactions that form Gases A 3 rd type of double-replacement reaction that occurs in aqueous solutions results in the formation of a gas. A 3 rd type of double-replacement reaction that occurs in aqueous solutions results in the formation of a gas. Common gases produced are: Common gases produced are: Carbon dioxide (CO 2 ) Carbon dioxide (CO 2 ) Hydrogen cyanide (HCN) Hydrogen cyanide (HCN) Hydrogen sulfide (H 2 S) Hydrogen sulfide (H 2 S)

21. Practice Problems Write the chemical, complete ionic, and net ionic equations for the reactions below, which all produce a gas. Write the chemical, complete ionic, and net ionic equations for the reactions below, which all produce a gas. Sulfuric acid reacts with sodium cyanide Sulfuric acid reacts with sodium cyanide Hydrochloric acid reacts with sodium sulfide Hydrochloric acid reacts with sodium sulfide Hydroiodic acid reacts with lithium sulfide Hydroiodic acid reacts with lithium sulfide

22. CO 2 Production When you combine any acidic solution and a carbonate (such as sodium hydrogen carbonate - aka sodium bicarbonate or baking soda), 2 reactions occur almost simultaneously. When you combine any acidic solution and a carbonate (such as sodium hydrogen carbonate - aka sodium bicarbonate or baking soda), 2 reactions occur almost simultaneously. HCl + NaHCO 3 H 2 CO 3 + NaCl double replacement HCl + NaHCO 3 H 2 CO 3 + NaCl double replacement H 2 CO 3 H 2 O (l) + CO 2 (g) decomposition H 2 CO 3 H 2 O (l) + CO 2 (g) decomposition

23. CO 2 Production By adding these 2 reactions, one chemical equation can be written. By adding these 2 reactions, one chemical equation can be written. HCl + NaHCO 3 H 2 CO 3 + NaCl HCl + NaHCO 3 H 2 CO 3 + NaCl H 2 CO 3 H 2 O (l) + CO 2 (g) H 2 CO 3 H 2 O (l) + CO 2 (g) HCl + NaHCO 3 NaCl + H 2 O (l) + CO 2 (g)

24. CO 2 Production Now take the overall equation and write a complete ionic equation and a net ionic equation. Now take the overall equation and write a complete ionic equation and a net ionic equation. HCl + NaHCO 3 NaCl + H 2 O (l) + CO 2 (g) HCl + NaHCO 3 NaCl + H 2 O (l) + CO 2 (g)

25. CO 2 Production Now take the overall equation and write a complete ionic equation and a net ionic equation. Now take the overall equation and write a complete ionic equation and a net ionic equation. HCl + NaHCO 3 NaCl + H 2 O (l) + CO 2 (g) HCl + NaHCO 3 NaCl + H 2 O (l) + CO 2 (g) H + + Cl - + Na + + HCO 3 - H + + Cl - + Na + + HCO 3 - Na + + Cl - + H 2 O (l) + CO 2 (g) Na + + Cl - + H 2 O (l) + CO 2 (g) H + + HCO 3 - H 2 O (l) + CO 2 (g) H + + HCO 3 - H 2 O (l) + CO 2 (g)

26. Practice Problems Write the chemical, complete ionic, and net ionic equations for the reactions below. Write the chemical, complete ionic, and net ionic equations for the reactions below. Perchloric acid (HClO 4 ) reacts with potassium carbonate Perchloric acid (HClO 4 ) reacts with potassium carbonate Hydrobromic acid reacts with ammonium carbonate Hydrobromic acid reacts with ammonium carbonate