10.3 reactions in aqueous solutions

1. 10.3 Reactions in Aqueous Solutions Objectives: Describe aqueous solutions Write complete ionic and net ionic equations for chemical reactions in aqueous solutions Predict whether reactions in aqueous solutions produce water precipitate or gas

3. Aqueous Solutions Although water is always the solvent in aqueous solution; there are many possible solutes. Example: Sucrose (Table sugar), Ethanol (grain alcohol) Most are molecular compounds that form ions when dissolved into water

4. Molecular Compound Hydrogen Chloride (referred to as hydrochloric acid) forms hydrogen ions and chloride ions when it dissolves in water

5. Ionic Compounds Ionic compounds may be solutes in aqueous solution Remember Ionic Compound contain positive ions and negative ions held together by ionic bonds The ions will separate when dissolved in water

6. Example (Aqueous Solution of ionic compound Sodium Hydroxide ) When two aqueous solutions contain ions as solutes are combined, ions may react with each other Always Double Replacement

7. Three types of products can form from Double Replacement Precipitate Water Gas

8. Reactions that form Precipitate Aqueous Solutions of Sodium hydroxide and Copper (II) Chloride are mixed, a double replacement reaction occurs in which the precipitate copper (II) hydroxide forms.

9. Some Notes�. Sodium hydroxide and copper (II) chloride are ionic compounds In aqueous solutions they exist as Na+, OH- Cu 2+ , and Cl- ions Solutions combine copper and hydroxide join to form the precipitate Copper (II) hydroxide and Na+ and Cl- ions remain dissolved in solution

10. Ionic Equations Chemists use ionic equations to show details of reactions that involve ions in aqueous solutions. Difference between ionic equations and chemical equations is that substances and written as ions.

11. Ionic Equations Complete Ionic Equation Ionic equation that shows all of the particles in a solution as they realistically exist Spectator ions Ions that do not participate in a reaction Previous example: Na+ and Cl- are spectator ions Net Ionic Equations Ionic equation that only includes the particles that participate in the reaction Net ionic equations are taken from complete ionic equations and spectator ions are crossed out

12. Example Write the chemical, complete ionic, and net ionic equations for the reaction between aqueous solutions of barium nitrate and sodium carbonate that forms the precipitate barium carbonate.

13. Reactions That Form Water Another type of double replacement reaction occurs in aqueous solutions produces water molecules. The water molecules produced will increase the number of solvent particles. There is no evidence of this occurring because it is colorless and odorless.

14. Example When you mix hydrobromic acid with a sodium hydroxide solution a double replacement reaction occurs and water is formed.

15. Continued In this case, the reactants and the product sodium bromide exist as ions . The complete ionic equation looks like this: If you look closely at the complete ionic equation. The reacting solute ions are the hydrogen and hydroxide ions because the sodium and bromine ions are both spectator ions.

16. Net Ionic Equation

17. Example Write the chemical, complete ionic, and net ionic equations for the reaction between hydrochloric acid and aqueous lithium hydroxide which produces water.

18. Reactions That Form Gases A third type of double replacement reaction occurs in aqueous solutions results in the formation of a gas Example: CO2, HCN, H2S

19. Continued A gas producing reaction occurs when you mix hydroiodic acid (HI) with an aqueous solution of lithium sulfide. Bubbles of hydrogen sulfide gas form in the container during the reaction. Also, Lithium Iodine is produced and remains dissolved in the solution.

20. Chemical Reaction 2HI(aq) + Li2S(aq) -> H2S(g) + 2LiI(aq) The reactants hydroiodic acid and lithium sulfide exist as ions in aqueous solution. Therefore, you can write an ionic equation for this reaction. The complete ionic equation includes all the substances in the solution. 2H+(aq)+ 2I-(aq) + 2Li+(aq) + S 2-(aq)-> H2S(g) + 2Li+(aq)+ 2I-(aq)

21. Net ionic Equation left Note, there are many spectator ions in the equation. When the spectator ions are crossed out, only the substances involved in the reaction remain in the equation.

22. The net ionic equation is�. 2H+ (aq) + S 2- (aq) -> H2S (g)

23. Example Baking soda and vinegar produces a carbon dioxide gas when they are mixed. Vinegar is an aqueous solution of acetic acid and water Baking soda consists of sodium hydrogen carbonate. A similar reaction can occur when you combine any acidic solution and sodium hydrogen carbonate to any solution. These two reactions occur at the same time, which one is a decomposition and single replacement

24. The reactions are:�

25. The two reactions can then be combined and represented by one chemical equation in a process similar to adding mathematical equations. An equation that combines two equations is called the overall equation.

26. Overall Equation To write an overall equation, the reactants in the two reaction are written on the reactant side of the combined reaction, and the products of the two equations are on the product side.

27. Example Reaction 1 � Reaction 2 � Combined Equation � � Overall Equation

28. The explanation The ions exist in an aqueous solution, therefore, a complete ionic equation can be written. Sodium and chloride are spectator ions. When you cross them out the only substances that take part in the reaction remain. The net ionic reaction shows that water and carbon dioxide are produced in this reaction.