1. Reactions in Aqueous Solutions
Chapter 8

2. Think, Pair, Share …
What are the signs of a chemical reaction?

3. Predicting Whether a Reaction Will Occur

4. Why do chemical reactions occur?
What causes reactants to “want” to form products?
Chemist’s have studied these reactions and have noticed several tendencies in reactants that drive them to form products.

5. The most common of these driving forces are:
Formation of a solid
Transfer of electrons
Formation of water
Formation of a gas
When two or more chemicals are brought together, if any of these things can occur, a chemical change (a reaction) is likely to take place.

6. Reactions in Which a Solid Forms

7. Forming a Precipitate
One driving force for a chemical reaction is the formation of a solid, a process called precipitation.
The solid that forms is called a precipitate.
This type of reaction is known as a precipitation reaction.
The fact that a solid forms tells us that a reaction – a chemical change – has occurred.

8. In virtually every case when a solid containing ions dissolves in water, the ions separate and move around independently.
We say that the ions of the solid dissociate when the solid dissolves in water.

9. When each unit of a substance that dissolves in water produces separated ions, the substance is called a strong electrolyte.

10. When ionic compounds dissolve, the resulting solution contains the separated ions.

11. How Do We Decide What Products Form?
Ideas?
As you can see this isn’t an easy question to answer.
Even an experienced Chemist wouldn’t be able to tell you exactly what will occur in a new chemical reaction.
Chemist’s use an educated guess to indicate what products are most likely to occur.

12. What are the possible products?
𝐾 2 𝐶𝑟 𝑂 4 (𝑎𝑞) +𝐵𝑎(𝑁 𝑂 3 ) 2 → ???
Discuss the possibilities with a partner
Remember to think of each as an ion

13. A solid compound must have a zero net charge
A solid compound must have a zero net charge. This means that the product of our reaction must contain both anions and cations (negative and positive ions).

14. What forms…
𝐾 2 𝐶𝑟 𝑂 4 (𝑎𝑞) +𝐵𝑎(𝑁 𝑂 3 ) 2 →𝐵𝑎𝐶𝑟 𝑂 4 𝑆 +𝐾𝑁 𝑂 3 (𝑎𝑞)

15. Predicting Precipitates
Soluble solid – a solid that readily dissolves in water.
Insoluble solid/Slightly soluble solid – a solid that dissolves to such a small degree that is not detectable to the naked eye.

16. General Rules for Solubility
Most nitrate salts are soluble.
Most salts of Na, K, and NH4 are soluble.
Most chloride salts are soluble.
Notable exceptions are AgCl, PbCl2, and Hg2Cl2
Most sulfate salts are soluble.
Notable exceptions are BaSO4, PbSO4, and CaSO4

17. General Rules for Solubility
Most hydroxide compounds are only slightly soluble.
The important exceptions are NaOH and KOH. Ba(OH)2 and Ca(OH)2 are moderately soluble.
Most sulfide, carbonate, and phosphate salts are only slightly soluble.

18. Describing Reactions in Aqueous Solution

19. 𝐾 2 𝐶𝑟 𝑂 4 (𝑎𝑞) +𝐵𝑎(𝑁 𝑂 3 ) 2 →𝐵𝑎𝐶𝑟 𝑂 4 𝑆 +𝐾𝑁 𝑂 3 (𝑎𝑞)
𝐾 2 𝐶𝑟 𝑂 4 (𝑎𝑞) +𝐵𝑎(𝑁 𝑂 3 ) 2 →𝐵𝑎𝐶𝑟 𝑂 4 𝑆 +𝐾𝑁 𝑂 3 (𝑎𝑞)
This is known as a molecular equation, it shows the complete formulas of all the reactants and products.

20. Complete Ionic Equation
In a complete ionic equation, all substances that are strong electrolytes are represented as ions.

21. Spectator Ions
Ions, that do not directly participate in a reaction in solution.

22. Net Ionic Equation
Includes only those components that are directly involved in the reaction.

23. Other Reactions in Aqueous Solutions
Section 8.2

24. Reactions that form water: Acids and Bases

25. Acids were first associated with the sour taste of citrus fruits.
The word acid comes from the Latin word acidus, which means sour.

26. Arrhenius Acids & Bases
Arrhenius, who was trying to discover why only certain solutions could conduct an electric current, found that conductivity arose from the presence of ions.

27. Arrhenius proposed that an acid is a substance that produces 𝐻 + ions (protons) when it is dissolved in water.

28. Studies show that when HCl, HNO3, and H2SO4 are placed in water virtually every molecule dissociates to give ions.
Because HCl, HNO3, and H2SO4 are strong electrolytes that produce 𝐻 + ions, they are called strong acids.

29. Arrhenius defined a base as a substance that produces hydroxide ions ( 𝑂𝐻 − ) in water.
Because these hydroxide compounds are strong electrolytes that contain 𝑂𝐻 − ions, they are called strong bases.

30. 𝐻 + (aq) + 𝑂𝐻 − (𝑎𝑞)  𝐻 2 𝑂 (𝑙)
When strong acids and strong bases (hydroxides) are mixed, the fundamental chemical change that always occurs is that 𝐻 + ions react with 𝑂𝐻 − ions to form water.
𝐻 + (aq) + 𝑂𝐻 − (𝑎𝑞)  𝐻 2 𝑂 (𝑙)

31. Reactions of Metals with Nonmetals (Oxidation-Reducation)

32. Oxidation-Reduction Reaction
A chemical reaction involving the transfer of electrons.

33. Characteristics of Oxidation-Reduction Reactions
When a metal reacts with a nonmetal, an ionic compound is formed.
The ions are formed when the metal transfers one or more electrons to the nonmetal, the metal atom becoming a cation and the nonmetal atom becoming a anion.
Therefore, a metal-nonmetal reaction can always be assumed to be an oxidation-reduction reaction, which involves electron transfer.

34. Characteristics of Oxidation-Reduction Reactions
Two nonmetals can also undergo an oxidation-reduction reaction.
At this point we can recognize these cases only by looking for 𝑂 2 as a reactant or product.
When two nonmetals react, the compound formed is not ionic.

35. Classifying Reactions

36. Single-Replacement
A + BC  B + AC
A single ion is being exchanged.

37. Double-Displacement Reaction
AB + CD  AD + CB

38. Combustion Reaction
A chemical reaction that involving oxygen as one of the reactants that produces enough heat so that a flame results.

39. Synthesis (Combination) Reactions
One of the most important activities in chemistry is the synthesis of new compounds.
When a given compound is formed from simpler materials, we call this a synthesis (combination) reaction.

40. Decomposition Reactions
A chemical reaction in which a compound is broken down into simpler compounds, or to the component elements.