Chemical Reactions

1. Chemical Reactions 9.3: Reactions in Aqueous Solutions

2. Objectives • Describe 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.

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

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

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 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.

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. • Recall that these reactions are double replacement reactions. • 3 types of products can form - a precipitate, water, or a gas.

8. Precipitate Reactions 2KI + Pb(NO3)2 2KNO3 + PbI2

9. The reaction in detail: K+ NO3- I- NO3- K+ NO3- Pb+2 NO3- K+ K+ I- KI and Pb(NO3)2 exist as IONS! PbI2(the precipitate)

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 complete ionic equation shows all the particles in a solution as they really exist. 2K+ + 2I- + Pb+2 + 2NO3- PbI2 (s) + 2K+ + 2NO3-

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. Na2CO3 + CuCl2 CuCO3 (s) + 2NaCl 2. 2Na+ + CO3-2 + Cu+2 + 2Cl- CuCO3 (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. AgNO3 + NaCl AgCl (s) + NaNO3 2. Ag+ + NO3- + Na+ + Cl- AgCl (s) + Na+ + NO3-

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. • Ag+ + Cl- AgCl (s) • Practice: 2K+ + 2I- + Pb+2 + 2NO3- PbI2 + 2K+ + 2NO32Na+ + CO3-2 + Cu+2 + 2Cl- CuCO3 (s) + 2Na+ + 2Cl-

17. More Practice! • 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 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. • Since water is colorless and odorless, there is no observable evidence that a reaction occurred. • HBr + NaOH NaBr + H2O • H+ + Br- + Na+ + OH- Na+ + Br-+ H2O • H+ + OH- H2O

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

20. Reactions that form Gases • A 3rd type of double-replacement reaction that occurs in aqueous solutions results in the formation of a gas. • Common gases produced are: • Carbon dioxide (CO2) • Hydrogen cyanide (HCN) • Hydrogen sulfide (H2S)

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

22. CO2 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. • HCl + NaHCO3 H2CO3 + NaCl double replacement • H2CO3 H2O (l) + CO2 (g) decomposition

23. CO2 Production • By adding these 2 reactions, one chemical equation can be written. HCl + NaHCO3 H2CO3 + NaCl H2CO3 H2O (l) + CO2 (g) HCl + NaHCO3 NaCl + H2O (l) + CO2 (g)

24. CO2 Production • Now take the overall equation and write a complete ionic equation and a net ionic equation. • HCl + NaHCO3 NaCl + H2O (l) + CO2 (g)

25. CO2 Production • Now take the overall equation and write a complete ionic equation and a net ionic equation. • HCl + NaHCO3 NaCl + H2O (l) + CO2 (g) • H+ + Cl- + Na+ + HCO3- Na+ + Cl- + H2O (l) + CO2 (g) • H+ + HCO3- H2O (l) + CO2 (g)

26. Practice Problems • Write the chemical, complete ionic, and net ionic equations for the reactions below. • Perchloric acid (HClO4) reacts with potassium carbonate • Hydrobromic acid reacts with ammonium carbonate