AP Chemistry Unit #4. Types of Chemical Reactions & Solution Stoichiometry

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AP Chemistry Unit #4 Chapter 4 Zumdahl & Zumdahl Types of Chemical Reactions & Solution Stoichiometry Students should be able to: Predict to some extent whether a substance will be a strong

1 AP Chemistry Unit #4 Chapter 4 Zumdahl & Zumdahl Types of Chemical Reactions & Solution Stoichiometry Students should be able to: Predict to some extent whether a substance will be a strong electrolyte, weak electrolyte, or nonelectrolyte. Predict the ions that an electrolyte dissociates into. Identify substances as acids, bases, and salts. Using solubility rules, predict if a precipitate forms in a metathesis reaction. Next, predict its products and write a balanced equation. Predict the products and write a balanced chemical equation for neutralization reactions. After constructing molecular reactions for metathesis reactions, be able to identify spectator ions and write the net ionic equations. Assign oxidation numbers to atoms. Determine whether a reaction is Redox (single replacement) or not. Use the activity series to predict whether a Redox reaction will occur and be able to write the molecular and net ionic equations if it does. Calculate moles of solute, volume of solution, or Molarity of the solution from the other two. Recognize and work dilution problems. Calculate the volume of a certain molarity solution required to react with another solution of known molarity. Calculate the mass of a substance that would be required to react with a given volume of a solution of known molarity. Calculate mass of solute or concentration of an unknown solution from titration data. Keywords: concentration molarity dilution titration standard solution equivalence point indicators aqueous solute solvent electrolyte nonelectrolyte strong electrolyte weak electrolyte activity series precipitate solubility metathesis molecular equation (complete) ionic equation net ionic equation spectator ions acids bases salts neutralization oxidation reduction redox reaction oxidation number

2 I. Aqueous Solutions A. What is an aqueous solution? B. What is the solvent? C. What is the solute? D. What does concentration mean? E. How do you measure molarity (M)? F. Sample Exercise 14.1 Calculate the molarity of a solution made by dissolving 23.4 g of sodium sulfate, Na 2 SO 4, in enough water to form 125 ml. G. Sample Exercise 14.2 How many grams of Na 2 SO 4 are required to make L of M Na 2 SO 4? 2

3 H. How do you make a dilution? 1. What is the formula that you can use? I. Sample Exercise 14.3 How much 3.0 M H 2 SO 4 would be required to make 500 ml of 0.10 M H 2 SO 4? II. Electrolytes A. Electrolyte vs. Nonelectrolyte B. Strong vs. Weak Electrolytes 1. What happens when an ionic substance dissolves? 3

C. Sample Exercise 4.4 What are the molar concentrations of all ions present in a 0.

4 C. Sample Exercise 4.4 What are the molar concentrations of all ions present in a M aqueous solution of calcium nitrate? III. Acids, Bases, and Salts A. What is an Acid? 1. What is the difference between a Monoprotic Acid and a Diprotic Acid? 4

5 2. What is the difference between a strong acid and a weak acid? 3. What are the strong acids? B. What is a Base? 1. What types of compounds make strong bases? C. What are Salts? D. What is a neutralization reaction? E. Sample Exercise 4.6 Write a balanced equation for the reaction of hydrobromic acid with barium hydroxide in aqueous solution. 5

6 IV. Ionic Equations A. Spectator Ions B. Net Ionic Equations C. Sample Exercise 4.7 Write the net ionic equation for the neutralization of two of the acidic hydrogens of phosphoric acid by sodium hydroxide in aqueous solution. V. Metathesis Reactions A. What is a Metathesis Reaction? B. What are the driving forces for a metathesis reaction? 6

7 C. Precipitation Reactions 1. Precipitate 2. Solubility D. Solubility Rules SOLUBLE SALTS Group I compounds and ammonium compounds Nitrates, hydrogen carbonates and chlorates Chlorides, bromides and iodides (EXCEPT those of Pb 2+, Ag + and Hg 2 2+ ) Sulfates (EXCEPT Ag +, Sr 2+, Ba 2+, Pb 2+ and Ca 2+ ) INSOLUBLE SALTS Hydroxides (EXCEPT Group I and ammonium, hydroxides of Ca 2+, Sr 2+ and Ba 2+ are slightly soluble) Carbonates, phosphates, chromates and sulfides (EXCEPT group I and ammonium salts, sulfides of group II are soluble) E. Sample Exercise 4.8 Write balanced molecular, ionic, and net ionic equations for the precipitation reactions (if any) that occur when solutions of the following compounds are mixed: (a) BaCl 2 and Na 2 SO 4 (b) KCl and Na 2 SO 4. 7

8 F. Reactions in which a weak electrolyte of nonelectrolyte forms: G. Reactions in which a Gas forms: H. Sample Exercise 4.9 Write balanced complete ionic and net ionic equations for any reactions that occur when the following compounds are mixed: (a) Cr(C 2 H 3 O 2 ) 2 (aq) and HNO 3 (aq) (b) FeCO 3 (s) and HCl (aq) (c) PbS (s) and H 2 SO 4 (aq). VI. Reactions of Metals A. Oxidation and Reduction 8

9 B. Oxidation of Metals by Acids and Salts C. Sample Exercise 4.10 Write the balanced molecular and net ionic equations for the reaction of aluminum with hydrobromic acid. D. The Activity Series Metal React with Acid? React with Steam React with Cold Water? Li YES YES YES K YES YES YES Ca YES YES YES Na YES YES YES Mg YES YES NO Al YES YES NO Zn YES YES NO Fe YES YES NO Sn YES NO NO Pb YES NO NO H - NO NO Cu NO NO NO Ag NO NO NO Pt NO NO NO Au NO NO NO 9

10 E. Sample Exercise 4.11 Will an aqueous solution of iron (II) chloride oxidize magnesium metal? If so, write the balanced molecular and net ionic equations for the reaction. VII. Solution Stoichiometry A. How to Solve Solution Stoichiometry Problems: 10

11 B. Sample Exercise 4.12 How many moles of H 2 O form when 25.0 ml of M HNO 3 solution is completely neutralized by NaOH? C. Titrations 1. Standard Solutions 2. Equivalence Point 3. Indicators 11

12 D. Sample Exercise 4.13 One method used commercially to peel potatoes is to soak them in a solution of NaOH for a short time, remove them from the NaOH, and spray off the peel. The concentration of NaOH is normally in the range 3 to 6 M. The NaOH is analyzed periodically. In one such analysis, 45.7 ml of M H 2 SO 4 is required to react completely with a 20.0 ml sample of NaOH solution: H 2 SO 4 (aq) + 2 NaOH (aq) 2 H 2 O (l) + Na 2 SO 4 (aq) What is the concentration of the NaOH solution? E. Sample Exercise 4.13 The quantity of Cl in a water supply is determined by titrating the sample with Ag + : Ag + (aq) + Cl (aq) AgCl (s) What mass of chloride ion is present in 10.0 g sample of the water if 20.2 ml of M Ag + is required to react with all the chloride in the sample? 12

13 VIII. Rules for assigning OXIDATION STATES (numbers): A. UNCOMBINED ELEMENTS (ELEMENTS NOT BONDED TO ANY OTHER TYPE OF ELEMENT) have an oxidation number of ZERO. This includes any formula that has only one chemical symbol in it (single elements & diatomic elements). Examples: B. In COMPOUNDS (remember, they are neutral and have 2+ different elements bonded together), the sum of the CHARGES must ADD UP TO ZERO so the ions within a compound have oxidation numbers equal to their OXIDATION # FOUND ON PERIODIC TABLE/INDIVIDUAL CHARGES. Ex: NaCl Ex: Mg 3 N 2 Ex: HNO 3 * The OXIDATION NUMBER is the number INSIDE the PARENTHESES. It is the charge on JUST ONE atom of that element! ** Remember that we almost always write the + ION FIRST and the - ION LAST in a compound formula. EXAMPLE: EXCEPTION to this rule: 13

14 C. GROUP 1 METALS always have an oxidation number of +1 when in a compound (bonded to another species). Likewise, combined GROUP 2 METALS always therefore have a +2 oxidation number when located within a compound. Ex: D. FLUORINE is always a -1 in compounds. The other HALOGENS (ex: Cl, Br) are also -1 as long as they are the most electronegative element in the compound. Ex: E. HYDROGEN is a +1 in compounds unless it is combined with a metal (and is at the back of the formula), then it is -1. Ex: F. OXYGEN is USUALLY -2 in compounds. Ex: When combined with fluorine (F), which is more electronegative, oxygen is +2. Ex: When in a PEROXIDE oxygen is -1. A peroxide is a compound that has a formula of X 2 O 2. Ex: G. The sum of the oxidation numbers in polyatomic ions must equal the CHARGE ON THE ION (SEE TABLE E). Ex: Cr 2 O

15 IX. Balancing Oxidation-Reduction Reactions A. Half Reactions red. ½ rxn: ox. ½ rxn: Sn 2+ (aq) + 2Fe 3+ (aq) Sn 4+ (aq) + 2Fe 2+ (aq) B. Balancing Redox Equations by the Half Reaction Method (in acidic solution) 1. Divide the equation into 2 incomplete half-reactions, one for oxidation, one for reduction. 2. Balance each half-reaction. (a) First, balance the elements other than H and O. (b) Next, balance the O atoms by adding H 2 O. (c) Then, balance the H atoms by adding H + (d) Finally, balance the charge by adding e to the side with the greater positive charge. 3. Multiply each half-reaction by an integer so that the number of electrons lost in the oxidation half-reaction is equal to the number of electrons gained by the reduction halfreaction. 4. Add the two half-reactions and simplify where possible by canceling species appearing on both sides of the equation. 5. Check the equation to make sure that there are the same number of atoms of each kind and the same total charge on both sides. Sample Exercise 4.19 Potassium dichromate (K 2 Cr 2 O 7 ) is a bright orange compound that can be reduced to a blue-violet solution of Cr +3 ions. Under certain conditions, K 2 Cr 2 O 7 reacts with ethyl alcohol (C 2 H 5 OH) as follows: H + (aq) + Cr 2 O 7 2 (aq) + C 2 H 5 OH(l) Acidic Cr 3+ (aq) + CO 2 (g) + H 2 O(l) Problem #63 p

16 C. Balancing Equations for reactions occuring in Basic Solutions Same as acidic solution except no excess H + can remain, so: 6. Consume any excess H + by adding OH - to that side, making water. Sample Exercise 4.20 Silver is sometimes found in nature as large nuggets; more often it is found mixed with other metals and their ores. An aqueous solution containing cyanide ion is often used to extract the silver using the following reaction that occurs in basic solution: Ag(s) + CN (aq) + O 2 (g) Basic Ag(CN) 2 - (aq) Problem #65 p

AP Chemistry Honors Unit Chemistry #4 2 Unit 3. Types of Chemical Reactions & Solution Stoichiometry

HO AP Chemistry Honors Unit Chemistry #4 2 Unit 3 Chapter 4 Zumdahl & Zumdahl Types of Chemical Reactions & Solution Stoichiometry Students should be able to:! Predict to some extent whether a substance