Reactions in Aqueous Solutions II: Calculations Chapter 11 Reactions in Aqueous Solutions II: Calculations 1 1 1 1 1 1 1 1

Aqueous Acid-Base Reactions Chapter Goals Aqueous Acid-Base Reactions Calculations Involving Molarity Titrations Calculations for Acid-Base Titrations Oxidation-Reduction Reactions Balancing Redox Equations Adding in H+, OH- , or H2O to Balance Oxygen or Hydrogen Calculations for Redox Titrations 2 2 2

Calculations Involving Molarity Example 11-1: If 100.0 mL of 1.00 M NaOH and 100.0 mL of 0.500 M H2SO4 solutions are mixed, what will the concentration of the resulting solution be? 2 2 2 2 3 3 3 3

Calculations Involving Molarity Example 11-2: If 130.0 mL of 1.00 M KOH and 100.0 mL of 0.500 M H2SO4 solutions are mixed, what will be the concentration of KOH and K2SO4 in the resulting solution? 5 5 5 6 6 6 6

Calculations Involving Molarity Example 11-3: What volume of 0.750 M NaOH solution would be required to completely neutralize 100 mL of 0.250 M H3PO4? You do it! 8 8 8 9 9 9 9

Titrations Acid-base Titration Terminology Titration – A method of determining the concentration of one solution by reacting it with a solution of known concentration. Primary standard – A chemical compound which can be used to accurately determine the concentration of another solution. Examples include KHP and sodium carbonate. Standard solution – A solution whose concentration has been determined using a primary standard. Standardization – The process in which the concentration of a solution is determined by accurately measuring the volume of the solution required to react with a known amount of a primary standard. 10 10 10 11 11 11 11

Titrations Acid-base Titration Terminology Indicator – A substance that exists in different forms with different colors depending on the concentration of the H+ in solution. Examples are phenolphthalein and bromothymol blue. Equivalence point – The point at which stoichiometrically equivalent amounts of the acid and base have reacted. End point – The point at which the indicator changes color and the titration is stopped. 10 10 10 11 11 11 11

Titrations 10 10 10 11 11 11 11

Calculations for Acid-Base Titrations Potassium hydrogen phthalate is a very good primary standard. It is often given the acronym, KHP. KHP has a molar mass of 204.2 g/mol. A very common mistake is for students to see the acronym KHP and think that this compound is made of potassium, hydrogen, and phosphorous. 11 11 11 12 12 12 12

Calculations for Acid-Base Titrations Example 11-4: Calculate the molarity of a NaOH solution if 27.3 mL of it reacts with 0.4084 g of KHP. 12 12 13 13 13 13

Calculations for Acid-Base Titrations Example 11-5: Calculate the molarity of a sulfuric acid solution if 23.2 mL of it reacts with 0.212 g of Na2CO3. You do it! 14 15 14 15 15 15

Calculations for Acid-Base Titrations Example 11-6: An impure sample of potassium hydrogen phthalate, KHP, had a mass of 0.884 g. It was dissolved in water and titrated with 31.5 mL of 0.100 M NaOH solution. Calculate the percent purity of the KHP sample. Molar mass of KHP is 204.2 g/mol. NaOH + KHP → NaKP + H2O You do it! 16 16 17 17 17 17

Calculations for Acid-Base Titrations Example 11-6: An impure sample of potassium hydrogen phthalate, KHP, had a mass of 0.884 g. It was dissolved in water and titrated with 31.5 mL of 0.100 M NaOH solution. Calculate the percent purity of the KHP sample. NaOH + KHP → NaKP + H2O 16 16 17 17 17 17

Oxidation-Reduction Reactions We have previously gone over the basic concepts of oxidation & reduction in Chapter 4. Rules for assigning oxidation numbers were also introduced in Chapter 4. Refresh your memory as necessary. We shall learn to balance redox reactions using the half-reaction method. 36 37 38 38 38

Balancing Redox Reactions Half reaction method rules: Write the unbalanced reaction. Break the reaction into 2 half reactions: One oxidation half-reaction and One reduction half-reaction Each reaction must have complete formulas for molecules and ions. Mass balance each half reaction by adding appropriate stoichiometric coefficients. To balance H and O we can add: H+ or H2O in acidic solutions. OH- or H2O in basic solutions. 38 37 39 39 39

Balancing Redox Reactions Charge balance the half reactions by adding appropriate numbers of electrons. Electrons will be products in the oxidation half-reaction. Electrons will be reactants in the reduction half-reaction. Multiply each half reaction by a number to make the number of electrons in the oxidation half-reaction equal to the number of electrons reduction half-reaction. Add the two half reactions. Eliminate any common terms and reduce coefficients to smallest whole numbers. 39 38 40 40 40

Balancing Redox Reactions Example 11-12: Tin (II) ions are oxidized to tin (IV) by bromine. Use the half reaction method to write and balance the net ionic equation. 40 39 41 41 41

Balancing Redox Reactions Example 11-13: Dichromate ions oxidize iron (II) ions to iron (III) ions and are reduced to chromium (III) ions in acidic solution. Write and balance the net ionic equation for the reaction. 44 43 45 45 45

Balancing Redox Reactions Example 11-14: In basic solution hydrogen peroxide oxidizes chromite ions, Cr(OH)4-, to chromate ions, CrO42-. The hydrogen peroxide is reduced to hydroxide ions. Write and balance the net ionic equation for this reaction. You do it! 48 47 50 50 49

Balancing Redox Reactions Example 11-15: When chlorine is bubbled into basic solution, it forms hypochlorite ions and chloride ions. Write and balance the net ionic equation. You do it! This is a disproportionation redox reaction. The same species, in this case Cl2, is both reduced and oxidized. 50 49 52 52 51

Balancing Redox Reactions Example 11-15: When chlorine is bubbled into basic solution, it forms hypochlorite ions and chloride ions. Write and balance the net ionic equation. 50 49 52 52 51

Calculations for Redox Titrations Just as we have done stoichiometry with acid-base reactions, it can also be done with redox reactions. 52 51 54 54 53

Calculations for Redox Titrations Example 11-16: What volume of 0.200 M KMnO4 is required to oxidize 35.0 mL of 0.150 M HCl? The balanced reaction is: You do it! 51 52 54 54 53

Calculations for Redox Titrations Example 11-17: A volume of 40.0 mL of iron (II) sulfate is oxidized to iron (III) by 20.0 mL of 0.100 M potassium dichromate solution. What is the concentration of the iron (II) sulfate solution? You do it! 53 54 56 56 55

Synthesis Question A 0.7500 g sample of an impure FeSO4 sample is titrated with 26.25 mL of 0.0200 M KMnO4 to an endpoint. What is the % purity of the FeSO4 sample?

Group Question Ice cubes that are made from water that is found in limestone rich areas of the country, such as Florida, have an unusual property. When a soft drink,like Coca-Cola, is poured over them an excessive amount of “fizzing” occurs. Write the molecular, total, and net ionic equations for the reaction that causes the excessive fizzing.