This unit introduces three classes of reactions; acid - base reactions, precipitation reactions and oxidation - reduction reactions. Virtually all chemical reactions fall into one of these reaction types. I realize that you may feel overwhelmed by the number of concepts introduced in this unit. Remember,this is just an "introduction" to these reactions and at least one chapter will be devoted to each reaction category later in the year.

How do you know a chemical change or reaction has occurred ? What would you observe to be able to answer the question affirmatively ? In our case, the common solvent for reactions in liquid environment is water, H2O. Evidence for a chemical reaction in this medium is one or more of the following, evolution of a gas, a color change or the formation of a precipitate. In some cases, in might be possible to discuss chemical change evidence associated with a temperature change but this criteria is not as sound as the three observable already indicated.

Acid - base reactions are introduced using the Arrhenius definition of an acid and a base. (See Section 4.4, page 170 and Screens 4.7, 4.8 and 4.9 ) An acid is any substance dissolved in water that increases the relative concentration of the species H(+),"hydrogen ions" or protons, in the resulting solution. A base using the Arrhenius concept, is any substance when dissolved in water results in the relative increase of the hydroxide ion, OH(-), in solution. You can check this site for a copy of a paper by Svante Arrhenius, "On the Dissociation of Substances Dissolved in Water" http:Arrhenius-dissociation.html

Precipitation reactions involve the formation of insoluble compounds by mixing an aqueous solutions containing the appropriate cations and anions which in the resulting "mixed" solution will interact to form the precipitated solid. The solubility rules guidelines presented in Figure 4.7, page 167 will be used to determine which ionic salts are expected to be soluble and which ionic salts are insoluble in water. You will need to refer to this figure to work some of the exercises and problems assigned in this unit.

Oxidation - reduction reactions involve the transfer of one or more electrons during the course of the reaction. In order to determine if a redox reaction has occurred, redox is "short" for reduction-oxidation, you must determine the oxidation numbers of all elements involved in both the reactants and the products. The "Guidelines for Determining Oxidation Numbers" are stated on page 191 of the text. You must become familiar with these "rules" for assigning oxidation numbers since they will become the basis for identifying whether a particular reaction belongs this class. Redox or electron tranfer reactions are important in many biochemical situations.

Reading Assignment:

Unit 2 Objectives: After completing Unit 2, you should be able to:

1. Balance simple chemical equations by "observation" A balanced chemical equation is balanced in the sens of "mass balance" for this objective. This is an application of the Law of Consevation of Mass in the conversion of reactants to products. ( Section 4.2 page 161 and Screen 4.2, 4.3 and 4.4 )

2.Discuss the difference between weak and strong electrolytes and non-electrolytes from the perspective of an aqueous solution environment. (Section 4.3, page 164 and Screen 4.5 )

3. Using the solubility guidelines, Figure 4.7, page 167, determine the solubility or insolubility of various ionic salts. Review the table of polyatomic anions and cations presented in Unit 1.( Text, pages 166 and 167 and Screens 4.11 and 4.12 )

4.Recognize and discuss acid-base reactions from the Arrenhius perspective where an acid is viewed as a source of hydrogen ions (protons), and a base is a source of hydroxide ions in water systems.( Section 4.8, page 181 and Screens 4.11 and 4.13 )

5.Using the "Guidelines for Determining OxidationNumbers", page 191, be able to find the oxidation numbers of elements in various compounds and ions. ( Section 4.10, page 188 and Screens 4.15, 4.16, 4.17 and 4.18)

6. Identify oxidation-reduction reactions based on finding different oxidation numbers for elements in compounds or ions as reactants as compared to the same elemnts in compounds or ions as products. Identify which species has been oxidized and which one has been reduced. Identify oxidizing agent and reducing agent on this basis. ( See 5 above for references)

e-Mail Activity: ( 15 points )

Return a brief comment and or discussion on ONE of the following items. Your response is due by 9:00 p.m. Thursday, 1/22 in order to recieve credit for the activity.

a) One of the major contributions of Arrhenius in the late 1800"s involved the discovery of the dissociation of ionic substances in water He suggested electrolytes conduct electricity in aqueous solutions because they dissociate into ions which can act as charge carriers. Discuss the dissocation of magnesium chloride, MgCl2 and ammonium nitrate, NH4(NO3) in water. Are these salts soluble in water according to the solubility table, page167 ? How many ions are in solution in each case ? Identify the cation and anion in each case. What about calcium carbonate, CaCO3 or silver chloride, AgCl ?

b) Why are oxidation-reduction reactions considered examples of electron transfer reactions ? If a species is oxidized, does it gain or lose electrons ? If a species is oxidized, does its oxidation number increase or decrease ? Can a reaction occur with only an oxidation and no reduction ?

Study Problems: Note: At least in the case of Chapter 4, most of the exercises and problems are duplicated in the workbook. It is probable the case for most chapters since the author of the text also wrote the workbook that comes with the ROM. Therefore, the "Workbook Activity" will contain most of the assigned activities for this unit.

Workbook Activities:

ROM Activities: Chapter 4: Screen 4.3, Exercise 4.2 ( same as Exercise 4.2 text), Screen 4.5, Screen 4.6, Exercise 4.3( same as Exercise 4.4 text ) , Screen 4.7, Exercise 4.4( same as Exercise 4.6 text ), Screen 4.7, Exercise 4.5 ( same as Exercise 4.7 text ), Screen 4.11, Screen 4.12, Exercise 4.6 ( same as Exercise 4.8 text ), Screen 4.15, Screen 4.16, Screen 4.17, Exercise 4.9 (same as Exercise 4.12 text ), Exercise 4.10 (same as Exercise 4.13 text ).

Study Questions - Workbook (Text Problems Numbers) 1 (15), 2 (17), 3 (19), 4 (21), 5 (23), 6 (25), 10 a,b (27), 11 (39), 18 (57), 19 (59), 20 (61), 21 (63), and 25 (73)

FAQ's Unit 2 Frequently Asked Questions-Unit 2

Answer Book Answers to Selected Problems-Unit 2

Practice Quiz Practice Quiz-Unit 2

Quiz 2 Unit 2 Quiz Available after Friday, January 23.

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