Chapter Four Learning Objectives. Ions in Aqueous Solution: Electrolytes

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Chapter Four Learning Objectives understand the nature of ions dissolved in water determine the products of and write chemical equations for precipitation, acid-base, and oxidation-reduction

1 Chapter Four Learning Objectives understand the nature of ions dissolved in water determine the products of and write chemical equations for precipitation, acid-base, and oxidation-reduction reactions recognize strong acids and strong bases and distinguish between the process of dissociation and ionization use molarity in solution stoichiometry and dilution calculations 1 Ions in Aqueous Solution: Electrolytes 2 1

2 Strong Electrolytes Strong electrolytes are compounds that exist in aqueous solution mostly as ions. Common examples are soluble ionic compounds and strong acids and bases: 3 4 2

What dissolved species are present in an aqueous solution of NaClO 4?

3 Ions in Aqueous Solution: Hydration When an ionic compound dissolves in water, H 2 O molecules separate, surround, and disperse the ions, a process called hydration: What property of water facilitates the hydration process? What dissolved species are present in an aqueous solution of NaClO 4? 5 Weak Electrolytes Weak electrolytes are molecular compounds that ionize to a very small extent in aqueous solution. Common examples are weak acids and bases: 6 3

Nonelectrolytes Nonelectrolytes are molecular substances that dissolve in water without forming ions: H 2 O CH 3 OH (l) H 2 O C 12 H 22 O 11 (s) CH 3 OH (aq) C 12 H

4 Nonelectrolytes Nonelectrolytes are molecular substances that dissolve in water without forming ions: H 2 O CH 3 OH (l) H 2 O C 12 H 22 O 11 (s) CH 3 OH (aq) C 12 H 22 O 11 (aq) If hydrogen chloride, HCl, is a molecular substance, then why does an aqueous solution of HCl conduct an electric current? 7 Precipitation Reactions 8 4

5 Key Concept Precipitation reactions are exchange reactions: AX + BY AY + BX AgNO 3 (aq) + NaCl (aq) AgCl (s) + NaNO 3 (aq) Predict the products (if any), including phase symbols, for each of the following: NaCl (aq) + K 2 SO 4 (aq) Fe(NO 3 ) 3 (aq) + (NH 4 ) 2 S (aq) + NaOH (aq) Pb(NO 3 ) 2 (aq) 9 Acids: Proton (H + ) Donors Acids are molecular compounds that ionize in water to produce H 3 O + (hydronium) ions: Strong and Weak Acids Classify each of the following acids as either strong or weak electrolytes: H 2 SO 4 (aq) + H 2 O (l) H 3 O + (aq) + HSO 4 (aq) HSO 4 (aq) + H 2 O (l) H 3 O + (aq) + SO 4 2 (aq) 10 5

6 Bases: Proton (H + ) Acceptors Bases produce OH ions when dissolved in water: H 2 O NaOH (s) Na + (aq) + OH (aq) Which equation above represents a physical change? 11 Acid-Base Neutralization Reactions Neutralization reactions between acids and metal hydroxides are another example of exchange reactions: HCl (aq) + NaOH (aq) H 2 O (l) + NaCl (aq) 3 HNO 3 (aq) + Fe(OH) 3 (s) 3 H 2 O (l) + Fe(NO 3 ) 3 (aq) Write a balanced chemical equation, including phase symbols, for the reaction between perchloric acid and aqueous strontium hydroxide: 12 6

Acid-Base Neutralization Reactions with Gas Formation You must recognize a special class of acid-base neutralization reactions between acids and metal carbonates or bicarbonates: Write a balanced

7 Acid-Base Neutralization Reactions with Gas Formation You must recognize a special class of acid-base neutralization reactions between acids and metal carbonates or bicarbonates: Write a balanced chemical equation, including phase symbols, for the reaction between solid iron (III) carbonate and sulfuric acid: 13 Oxidation-Reduction (Redox) Reactions Redox reactions involve the transfer of electrons between substances. If one substance loses electrons (oxidation), then another substance must gain those electrons (reduction). 14 7

8 Recognizing Redox Reactions: Oxidation Numbers Which of the following are redox reactions? Ca (s) + 2 H 2 O (l) H 2 (g) + Ca(OH) 2 (s) Cu(OH) 2 (s) + 2 HBr (aq) 2 H 2 O (l) + CuBr 2 (aq) Sr(NO 3 ) 2 (aq) + H 2 SO 4 (aq) SrSO 4 (s) + 2 HNO 3 (aq) 2 KClO 3 (s) 2 KCl (s) + 3 O 2 (g) The application of oxidation numbers provides a direct way of tracking the transfer of electrons, if any, through the course of the reaction. 15 Assigning Oxidation Numbers 1. For an atom in its elemental form, the oxidation number is always zero. 2. For monatomic ions, the oxidation number equals the charge on the ion. 3. For nonmetals within molecules or polyatomic ions, hydrogen is usually +1, oxygen is usually 2, and the halogens are usually The sum of the oxidation numbers is zero for neutral compounds or equals the charge for polyatomic ions. 16 8

9 Practice Exercise Assign an oxidation number to every atom in each of the following: (a)bacl 2 (d)so 4 2 (b)ccl 4 (e)fe(no 3 ) 3 (c) S 8 (f) HClO 4 17 Key Concept An increase in oxidation number indicates oxidation and a decrease in oxidation number indicates reduction: Which reactant is the reducing agent and which is the oxidizing agent in the above reaction? 18 9

Metals by Acids and Salts Metals at the top of the table have the strongest tendency to

10 Indicate which element is oxidized and which is reduced in the following reaction: Practice Exercise 2 H 2 O 2 (l) 2 H 2 O (l) + O 2 (g) 19 Predicting the Oxidation of Metals by Acids and Salts Metals at the top of the table have the strongest tendency to lose electrons. Any metal higher in the series will reduce the ion of any metal lower in the series

11 Key Concept The oxidation of metals by acids and salts are displacement reactions: 3 K (s) + Cr(ClO 4 ) 3 (aq) 3 KClO 4 (aq) + Cr (s) Ca (s) + 2 HNO 3 (aq) Ca(NO 3 ) 2 (aq) + H 2 (g) Predict the products (if any), including phase symbols, for each of the following: Mn (s) + FeCl 3 (aq) HNO 3 (aq) + Au (s) Al (s) + HCl (aq) Formation of Silver Crystals 21 Expressing Concentration moles solute molarity (M) = 1 L solution The solute is the minority component of any solution. What is the solvent or the majority component of all aqueous solutions? How many milliliters of M CaCl 2 contain 2.76 g of solute? 22 11

molarity (M) volume (V) = moles solute (a constant) M = 1V1 M2V2 How many milliliters of 5.

12 Diluting Concentrated Solutions For convenience, chemicals are typically bought and stored as concentrated stock solutions that are then diluted for use in the laboratory: moles of solute before dilution = moles solute after dilution molarity (M) volume (V) = moles solute (a constant) M = 1V1 M2V2 How many milliliters of 5.0 M K 2 Cr 2 O 7 must be diluted to prepare ml of 0.10 M K 2 Cr 2 O 7? 23 Solution Molarity is a useful conversion factor between moles and volume: 24 12

Practice Exercise The odor of skunks is caused by sulfur-containing compounds called thiols, such as C 4 H 10 S, which can be deodorized by reaction with household bleach: 2 C 4 H 10 S (l) + NaClO

13 Practice Exercise The odor of skunks is caused by sulfur-containing compounds called thiols, such as C 4 H 10 S, which can be deodorized by reaction with household bleach: 2 C 4 H 10 S (l) + NaClO (aq) C 8 H 18 S 2 (l) + NaCl (aq) + H 2 O (l) How many milliliters of C 4 H 10 S (0.830 g/ml) can be deodorized using L of M NaClO? 25 Integrative Exercise You mix ml of 2.34 M FeCl 3 with ml of 4.53 M NaOH and observe a precipitate. (a)how many moles of the solid precipitate are formed in the reaction? (b)what is the molar concentration of the excess reactant remaining in solution after the reaction? 26 13

Chapter 4: Types of Chemical reactions and Solution Stoichiometry

Chapter 4: Types of Chemical reactions and Solution Stoichiometry 4.1 Water, The Common Solvent State why water acts as a common solvent. Draw the structure of water, including partial charge. Write equations