Aqueous Reactions and Solution Stoichiometry What is aqueous

Aqueous Reactions and Solution Stoichiometry • • What is aqueous? What is an aqueous reaction? What are some types of aqueous reactions? Why might these be important? Give examples. • Aqueous reactions cannot take place without water. What do you already know about water that will help us understand aqueous reactions? Aqueous Reactions

Solutions: • Homogeneous mixtures of two or more pure substances. • The solvent is present in greatest abundance. • All other substances are solutes. Aqueous Reactions

Dissociation • When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them. • This process is called dissociation. Aqueous Reactions

Electrolytes • Substances that dissociate into ions when dissolved in water. Example: Na. Cl • A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so. Example: C 12 H 22 O 11 Notice, solubility does not imply that something is or is not an electrolyte. Aqueous Reactions

Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes. Aqueous Reactions

Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases. Aqueous Reactions

SAMPLE EXERCISE 4. 1 Relating Relative Numbers of Anions and Cations to Chemical Formulas The diagram below represents an aqueous solution of one of the following compounds: Mg. Cl 2 , KCl, or K 2 SO 4. Which solution does it best represent? Aqueous Reactions

SAMPLE EXERCISE 4. 1 Relating Relative Numbers of Anions and Cations to Chemical Formulas The diagram below represents an aqueous solution of one of the following compounds: Mg. Cl 2 , KCl, or K 2 SO 4. Which solution does it best represent? Solution Analyze: We are asked to associate the charged spheres in the diagram with ions present in a solution of an ionic substance. Plan: We examine the ionic substances given in the problem to determine the relative numbers and charges of the ions that each contains. We then correlate these charged ionic species with the ones shown in the diagram. Solve: The diagram shows twice as many cations as anions, consistent with the formulation K 2 SO 4. Aqueous Check: Notice that the total net charge in the diagram is zero, as it must be if it is to represent an ionic Reactions substance.

Electrolytes • A strong electrolyte dissociates completely when dissolved in water. • A weak electrolyte only dissociates partially when dissolved in water. Aqueous Reactions

Aqueous Reactions

Strong Electrolytes Are… • Strong acids Aqueous Reactions

Strong Electrolytes Are… • Strong acids • Strong bases Aqueous Reactions

Strong Electrolytes Are… • Strong acids • Strong bases • Soluble ionic salts Aqueous Reactions

Precipitation Reactions When one mixes ions that form compounds that are insoluble (as could be predicted by the solubility guidelines), a precipitate is formed. Aqueous Reactions

Metathesis (Exchange) Reactions a. k. a. Double Replacement Rxns • Metathesis comes from a Greek word that means “to transpose” Ag. NO 3 (aq) + KCl (aq) Ag. Cl (s) + KNO 3 (aq) Aqueous Reactions

Metathesis (Exchange) Reactions a. k. a. Double Replacement Rxns • Metathesis comes from a Greek word that means “to transpose” • It appears the ions in the reactant compounds exchange, or transpose, ions Ag. NO 3 (aq) + KCl (aq) Ag. Cl (s) + KNO 3 (aq) Aqueous Reactions

Metathesis (Exchange) Reactions • Metathesis comes from a Greek word that means “to transpose” • It appears the ions in the reactant compounds exchange, or transpose, ions Ag. NO 3 (aq) + KCl (aq) Ag. Cl (s) + KNO 3 (aq) Aqueous Reactions

Ag. NO 3 (aq) + KCl (aq) Ag. Cl (s) + KNO 3 (aq) How did we know that silver chloride was a solid? ? ? We checked the solubility table. Aqueous Reactions

Aqueous Reactions

Predict the products of the following reactions • Ba. Cl 2 (aq) + K 2 SO 4 (aq) • Fe 2(SO 4)3 (aq) + Li. OH (aq) • Mg(NO 3)2 (aq) + Ca. S (aq) • Na. Cl (aq) + KNO 3 (aq) Aqueous Reactions

Predict the products of the following reactions • Ba. Cl 2 (aq) + K 2 SO 4 (aq) • → Ba. SO 4 (s) + 2 KCl (aq) • Fe 2(SO 4)3 (aq) + 6 Li. OH (aq) • → 2 Fe(OH)3 (s) + 3 Li 2 SO 4 (aq) • Mg(NO 3)2 (aq) + Ca. S (aq) • → Mg. S (s) + Ca(NO 3)2 (aq) • Na. Cl (aq) + KNO 3 (aq) • → Na. NO 3 (aq) + KCl (aq) or NR Aqueous Reactions

Solution Chemistry • It is helpful to pay attention to exactly what species are present in a reaction mixture (i. e. , solid, liquid, gas, aqueous solution). • If we are to understand reactivity, we must be aware of just what is changing during the course of a reaction. Aqueous Reactions

Molecular Equation The molecular equation lists the reactants and products in their molecular form. Ag. NO 3 (aq) + KCl (aq) Ag. Cl (s) + KNO 3 (aq) Aqueous Reactions

Ionic Equation • In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. • This more accurately reflects the species that are found in the reaction mixture. Ag+ (aq) + NO 3 - (aq) + K+ (aq) + Cl- (aq) Ag. Cl (s) + K+ (aq) + NO 3 - (aq) Aqueous Reactions

Net Ionic Equation • To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. Ag+(aq) + NO 3 -(aq) + K+(aq) + Cl-(aq) Ag. Cl (s) + K+(aq) + NO 3 -(aq) Aqueous Reactions

Net Ionic Equation • To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. • The only things left in the equation are those things that change (i. e. , react) during the course of the reaction. Ag+(aq) + Cl-(aq) Ag. Cl (s) Aqueous Reactions

Net Ionic Equation • To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. • The only things left in the equation are those things that change (i. e. , react) during the course of the reaction. • Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions. Ag+(aq) + NO 3 -(aq) + K+(aq) + Cl-(aq) Ag. Cl (s) + K+(aq) + NO 3 -(aq) Aqueous Reactions

Writing Net Ionic Equations 1. Write a balanced molecular equation. 2. Dissociate all strong electrolytes. 3. Cross out anything that remains unchanged from the left side to the right side of the equation. 4. Write the net ionic equation with the species that remain. Aqueous Reactions

Writing Net Ionic Equations Write the net ionic equation for each reaction • Pb(NO 3)2 (aq) + KI (aq) • Li 2 S (aq) + Ba. Br 2 (aq) • NH 4 Cl (aq) + Sr(OH)2 (aq) Aqueous Reactions

Writing Net Ionic Equations Write the net ionic equation for each reaction • Pb(NO 3)2 (aq) + 2 KI (aq) • → Pb. I 2 (s) + 2 K(NO 3) (aq) Pb 2+ + 2 I- → Pb. I 2 (s) • Li 2 S (aq) + Ba. Br 2 (aq) • → Li. Br (aq) + Ba. S (aq) 2 Li+ (aq) + S-2 (aq) + Ba 2+ (aq) + 2 Br- (aq) → 2 Li+ (aq) + 2 Br- (aq) + Ba 2+ (aq) + S-2 (aq) Notice …. all spectator ions. They all cancel and therefore, no reaction occurs. • 2 NH 4 Cl (aq) + Sr(OH)2 (aq) • → Sr. Cl 2 (aq) + 2 NH 4 OH (aq) 2 NH 4+ (aq) + 2 Cl- (aq) + Sr 2+ (aq) + 2 OH- (aq) → Sr 2+ (aq) + 2 Cl- (aq) + 2 NH 4+ (aq) + 2 OH(aq) Notice …. all spectator ions. They all cancel and therefore, no reaction occurs. Aqueous Reactions

Acids: • Substances that increase the concentration of H+ when dissolved in water (Arrhenius). • Proton donors (Brønsted–Lowry). Aqueous Reactions

Acids There are only seven strong acids: • • Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Nitric (HNO 3) Sulfuric (H 2 SO 4) Chloric (HCl. O 3) Perchloric (HCl. O 4) These substances are consider strong acids because they do not just dissolve in water, they will completely dissociate. Aqueous Reactions

Bases: • Substances that increase the concentration of OH− when dissolved in water (Arrhenius). • Proton acceptors (Brønsted–Lowry). Aqueous Reactions

Bases The strong bases are the soluble salts of hydroxide ion: • • Alkali metals Calcium Strontium Barium Aqueous Reactions

Acid-Base Reactions In an acid-base reaction, the acid donates a proton (H+) to the base. Aqueous Reactions

Neutralization Reactions Generally, when solutions of an acid and a base are combined, the products are a salt and water. HCl (aq) + Na. OH (aq) Na. Cl (aq) + H 2 O (l) Aqueous Reactions

Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + Na. OH (aq) Na. Cl (aq) + H 2 O (l) H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) Na+ (aq) + Cl- (aq) + H 2 O (l) Aqueous Reactions

Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + Na. OH (aq) Na. Cl (aq) + H 2 O (l) H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) Na+ (aq) + Cl- (aq) + H 2 O (l) H+ (aq) + Cl- (aq) + Na+ (aq) + OH- (aq) Na+ (aq) + Cl- (aq) + H 2 O (l) H+ (aq) + OH- (aq) → H 2 O (l) Aqueous Reactions

Neutralization Reactions What does this have to do with you? ? ? What happens when you have a stomach ache? What do you do about it? Why? Aqueous Reactions

Neutralization Reactions What does this have to do with you? ? ? Many antacids contain magnesium hydroxide. It undergoes a neutralization reaction with stomach acid. What acid constitutes the largest quantity of stomach acid? Write a net ionic equation for the neutralization reaction between magnesium hydroxide and hydrochloric acid. Mg(OH)2 (s) + H+ (aq) → Mg 2+ (aq) + H 2 O (l) Aqueous Reactions

Neutralization Reactions Observe the reaction between Milk of Magnesia, Mg(OH)2, and HCl. Can you overdoes on antacid? ? What do you think would happen? Aqueous Reactions

Gas-Forming Reactions • These metathesis reactions do not give the product expected. • The expected product decomposes to give a gaseous product (CO 2 or SO 2). Ca. CO 3 (s) + HCl (aq) Ca. Cl 2 (aq) + CO 2 (g) + H 2 O (l) Na. HCO 3 (aq) + HBr (aq) Na. Br (aq) + CO 2 (g) + H 2 O (l) Sr. SO 3 (s) + 2 HI (aq) Sr. I 2 (aq) + SO 2 (g) + H 2 O (l) Aqueous Reactions

Gas-Forming Reactions • This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! • Just as in the previous examples, a gas is formed as a product of this reaction: Na 2 S (aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + H 2 S (g) Aqueous Reactions

A Carbonated Beverage is Another Example How is a beverage carbonated? What happens to the dissolved gas? H 2 O (l) + CO 2 (g) ↔ H 2 CO 3 (aq) H 2 O (l) + CO 2 (g) ↔ 2 H+ (aq) + CO 3 -2 (aq) Aqueous Reactions

Oxidation-Reduction Reactions • An oxidation occurs when an atom or ion loses electrons. (It becomes more positive) • A reduction occurs when an atom or ion gains electrons. (It becomes more negative) Aqueous Reactions

Oxidation-Reduction Reactions One cannot occur without the other. Aqueous Reactions

Oxidation Numbers To determine if an oxidation-reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity. Aqueous Reactions

Oxidation Numbers • Elements in their elemental form have an oxidation number of 0. • The oxidation number of a monatomic ion is the same as its charge. Aqueous Reactions

Oxidation Numbers • Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. ØOxygen has an oxidation number of − 2, except in the peroxide ion in which it has an oxidation number of − 1. ØHydrogen is − 1 when bonded to a metal, +1 when bonded to a nonmetal. Aqueous Reactions

Oxidation Numbers • Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. ØFluorine always has an oxidation number of − 1. ØThe other halogens have an oxidation number of − 1 when they are negative; they can have positive oxidation numbers, Aqueous however, most notably in oxyanions. Reactions

Oxidation Numbers • The sum of the oxidation numbers in a neutral compound is 0. • The sum of the oxidation numbers in a polyatomic ion is the charge on the ion. Aqueous Reactions

Oxidation Numbers Find the oxidation numbers for each of the following species. • • • CO 32 H 2 S S 8 SCl 2 SO 42 Cr 2 O 72 Aqueous Reactions

• • • CO 32 C = +4 and O = -2 H 2 S H = +1 and S = -2 S 8 S=0 SCl 2 S = +2 and Cl = -1 SO 42 S = +6 and O = -2 Cr 2 O 72 Cr = +6 and O = -2 Aqueous Reactions

Examine each Reaction below and Identify the oxidized and reduced reagents • 2 K (s) + 2 H 2 O (l) → 2 KOH (aq) + H 2 (g) • Fe 2 O 3 (s) + 2 Al (s) → 2 Fe (l) + Al 2 O 3 (s) • Si (s) + 2 Cl 2 (g) → Si. Cl 4 (l) Aqueous Reactions

Examine each Reaction below and Identify the oxidized and reduced agents • 2 K (s) + 2 H 2 O (l) → 2 KOH (aq) + H 2 (g) K (s) → K+ (aq), it was oxidized; Hydrogen was reduced in water to form hydrogen gas. • Fe 2 O 3 (s) + 2 Al (s) → 2 Fe (l) + Al 2 O 3 (s) Aluminum metal is oxidized; iron is reduced • Si (s) + 2 Cl 2 (g) → Si. Cl 4 (l) Si is oxidized while Cl is reduced Aqueous Reactions

Which three of the following reactions are Red-Ox? What is oxidized and what is reduced? Zn (s) + 2 NO 3 - (aq) + 4 H+ (aq) → Zn+2 (aq) + 2 NO 2 (g) + 2 H 2 O (l) Zn(OH)2 (s) + H 2 SO 4 (aq) → Zn. SO 4 (aq) + 2 H 2 O (l) Ca (s) + 2 H 2 O (l) → Ca(OH)2 (s) + H 2 (g) 4 Fe(OH)2 (s) + 2 H 2 O (l) + O 2 (g) → 4 Fe(OH)3 (aq) Aqueous Reactions

Which three of the following reactions are Red-Ox? What is oxidized and what is reduced? Zn (s) + 2 NO 3 - (aq) + 4 H+ (aq) → Zn+2 (aq) + 2 NO 2 (g) + 2 H 2 O (l) Red-ox: zinc is oxidized, nitrogen is reduced Zn(OH)2 (s) + H 2 SO 4 (aq) → Zn. SO 4 (aq) + 2 H 2 O (l) Not Red-ox Ca (s) + 2 H 2 O (l) → Ca(OH)2 (s) + H 2 (g) Red-ox: calcium is oxidized, hydrogen is reduced 4 Fe(OH)2 (s) + 2 H 2 O (l) + O 2 (g) → 4 Fe(OH)3 (aq) Red-ox: Iron is oxdized, oxygen is reduced Aqueous Reactions

Displacement Reactions a. k. a. Single Replacement Reactions • In displacement reactions, ions oxidize an element. • The ions, then, are reduced. Aqueous Reactions

Displacement Reactions In this reaction, silver ions oxidize copper metal. Cu (s) + 2 Ag+ (aq) Cu 2+ (aq) + 2 Ag (s) Aqueous Reactions

Displacement Reactions The reverse reaction, however, does not occur. x Cu (s) + 2 Ag+ (aq) Cu 2+ (aq) + 2 Ag (s) Aqueous Reactions

Activity Series Aqueous Reactions

Use the Activity Series to predict the products of the following reactions. If the reactions does take place, write the net ionic equation for the reaction. Lastly, identify the species being oxidized and reduced. • Al (s) + HBr (aq) • Fe(s) + KI (aq) • Zn (s) + Ni(NO 3)2 (aq) Aqueous Reactions

• 2 Al (s) + 6 HBr (aq) → 2 Al. Br 3 (aq) + 3 H 2 (g) 2 Al (s) + 6 H+ (aq) → 2 Al 3+ (aq) + 3 H 2(g) Aluminum is oxidized and Hydrogen is reduced. • Fe(s) + KI (aq) No Reaction • Zn (s) + Ni(NO 3)2 (aq) → Zn(NO 3)2 (aq) + Ni (s) Zn (s) + Ni 2+ (aq) → Zn 2+ (aq) + Ni (s) Zinc is oxidized and Nickel is reduced. Aqueous Reactions

Molarity • Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. (For example, it would be much more dangerous to spill a high concentration of hydrochloric acid on your hand than a low concentration) • Molarity is one way to measure the concentration of a solution. moles of solute Molarity (M) = volume of solution in liters Aqueous Reactions

Mixing a Solution • How many grams of silver nitrate are required to make 100 m. L of a 0. 5 M solution? • How many grams of Na. OH are required to make 50 m. L of an 8. 2 M solution? Aqueous Reactions

Mixing a Solution • How many grams of silver nitrate are required to make 100 m. L of a 0. 5 M solution? 9 grams • How many grams of Na. OH are required to make 50. 0 m. L of an 8. 2 M solution? 16 grams Aqueous Reactions

Dilution M 1 V 1 = M 2 V 2 Aqueous Reactions

Dilution • You have 1 L of a 1. 00 M stock solution of hydrochloric acid. You need to make 500 m. L of a 0. 20 M solution. How much of the stock solution is needed? • You need to make 100 m. L of 0. 50 M nitric acid. The storage bottle reads 6. 0 M. How much of the 6. 0 M nitric acid will you need? Aqueous Reactions

Dilution • You have 1 L of a 1. 00 M stock solution of hydrochloric acid. You need to make 500 m. L of a 0. 20 M solution. How much of the stock solution is needed? 100. m. L or 0. 100 L • You need to make 100 m. L of 0. 50 M nitric acid. The storage bottle reads 6. 0 M. How much of the 6. 0 M nitric acid will you need? 8. 3 m. L Aqueous Reactions

Using Molarities in Stoichiometric Calculations How many grams of Ca(OH)2 are needed to neutralize 20. 0 m. L of a 0. 150 M H 2 SO 4 solution? 0. 222 g Aqueous Reactions

Using Molarities in Stoichiometric Calculations How many liters of 0. 500 M HCl are needed to react completely with 0. 100 mol Pb(NO 3)2, forming the precipitate Pb. Cl 2? 0. 400 L Aqueous Reactions

Titration The analytical technique in which one can calculate the concentration of a solute in a solution. Aqueous Reactions

Titration Aqueous Reactions

Titration Example A 1. 034 -g sample of impure oxalic acid (H 2 C 2 O 4) is dissolved in water and an acidbase indicator is added. The sample required 34. 47 m. L of 0. 485 M Na. OH to reach the equivalence point. What is the mass of oxalic acid and what is its mass percent in the sample? 0. 752 g H 2 C 2 O 4 and 72. 7% H 2 C 2 O 4 Aqueous Reactions

Titration A 0. 263 -g sample of sodium carbonate requires 28. 35 m. L of aqueous HCl for titration to the equivalence point. What is the molarity of the HCl? 0. 175 M HCl Aqueous Reactions

Courtesy of http: //www. siraze. net/chemistry/sezennur/subjects/comics 01. htm Aqueous Reactions