CHAPTER 4. Major Classes of Chemical Reactions

Transcription

1 CHAPTER 4 Major Classes of Chemical Reactions

2 There are several types of reaction. 1. ADDITION REACTION A + B C 2. DECOMPOSITION A B + C 3. SINGLE DISPLACEMENT AB + C AC + B 4. DOUBLE DISPLACEMENT AB + CD AC + BD 5. COMPLEX REACTIONS

3 There are several types of reaction, but for now we will just survey three (3) that occur in aqueous solutions: 1. PRECIPITATION REACTIONS 2. ACID-BASE REACTIONS 3. OXIDATION-REDUCTION REACTIONS

4 WATER is a very important medium for reactions to occur. WATER IS POLAR Compounds become SOLVATED

5 When water solvates ionic compounds, the ions are free to move. When charges are free to move, they can conduct electricity!

6 Molecules that allow electricity to flow in aqueous solutions are called electrolytes. Those that do not are called nonelectrolytes. Ionic compounds = strong electrolytes Covalent compounds = weak electrolytes or nonelectrolytes

7 Writing equations in aqueous solutions involve three (3) levels. The molecular equation shows all of the reactants and products as intact, undissociated compounds. The total ionic equation shows all of the soluble ionic substances dissociated into ions. The net ionic equation omits the spectator ions and shows the actual chemical change taking place.

8 Writing equations in aqueous solutions involve three (3) levels.

9 Precipitation Reactions

10 Precipitation Reactions occur when mixing two reactants produce an insoluble product called precipitate. NaI(aq) + Pb(NO 3 ) 2 (aq) PbI 2 (s) + NaNO 3 (aq) 2NaI(aq) + Pb(NO 3 ) 2 (aq) PbI 2 (s) + 2NaNO 3 (aq) 2Na + (aq) + 2I - (aq) + Pb 2+ (aq) + 2NO 3- (aq) PbI 2 (s) + 2Na + (aq) + 2NO 3- (aq) 2NaI(aq) + Pb(NO 3 ) 2 (aq) PbI 2 (s) + 2NaNO 3 (aq)

11 Predicting precipitate formation is based on the solubility rules.

12 Predicting precipitate formation is based on the solubility rules.

13 Predicting precipitate formation is based on the solubility rules. Predict whether a reaction occurs when each of the following pairs of solutions are mixed. If a reaction does occur, write balanced molecular, total ionic, and net ionic equations, and identify the spectator ions. (a) Potassium fluoride(aq) + strontium nitrate(aq) (b) Ammonium perchlorate(aq) + sodium bromide(aq)

14 Predicting precipitate formation is based on the solubility rules.

15 Predicting precipitate formation is based on the solubility rules.

16 Predicting precipitate formation is based on the solubility rules. Aluminum sulfate, known as cake alum, has a wide range of uses, from dyeing leather and cloth to purifying sewage. In aqueous solutions, it reacts with base to form a white precipitate. a. Write a balanced TOTAL and NET IONIC equation for its reaction with aqueous NaOH b. What mass of precipitate forms when ml of M NaOH is added to 627 ml of a solution containing 15.8 g of aluminum sulfate per liter.

17 Acid-Base Reactions

18 Acids are compounds that produces H+ when dissolved in water. Bases are substances that produce OH- when dissolved in water. HCl (g) + H 2 O (l) H + (aq) + Cl - (aq) NaOH (s) + H 2 O (l) Na + (aq) + OH - (aq)

19 Strong acids and bases are strong electrolytes. Weak acids and bases are strong electrolytes

20 Acids and bases react in a neutralization reaction: FORMATION OF H 2 O from H + and OH - H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq) Na + (aq) + Cl - (aq) + H 2 O (l) H + (aq) + OH - (aq) H 2 O (l)

21 Neutralization reactions are just proton transfer reactions from one species to another.

22 Chemists study acid-base reactions through titration. In titration, one solution of known concentration is used to determine the concentration of another solution through a monitored reaction.

23 Chemists study acid-base reactions through titration. In titration, one solution of known concentration is used to determine the concentration of another solution through a monitored reaction. Titrant solution of known concentration which is accurately delivered using a buret Analyte solution of unknown concentration which reacts with the titrant Indicators compounds which do not participate in the general reaction between analyte and titrant, but are indirectly affected by the reaction producing notable changes. They are used to monitor the reaction. Some reactions also produce self-indicators.

24 Chemists study acid-base reactions through titration. In titration, one solution of known concentration is used to determine the concentration of another solution through a monitored reaction. basic acidic change occurs over ~2 ph units

25 Chemists study acid-base reactions through titration. In titration, one solution of known concentration is used to determine the concentration of another solution through a monitored reaction. Equivalence point the point where equivalent amount of titrant reacts with that of the analyte (all moles of H + react with all moles of OH - ) End point the ph range where the indicator changes color

26 Chemists study acid-base reactions through titration. In titration, one solution of known concentration is used to determine the concentration of another solution through a monitored reaction. You perform an acid-base titration to standardize an HCl solution by placing ml of HCl in a flask with a few drops of indicator solution. You put M NaOH into the buret, and the initial reading is 0.55 ml. At the end point, the buret reading is ml. What is the concentration of the HCl solution? What volume of M Ba(OH) 2 would neutralize ml of the HCl solution standarized in the preceding example.