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Chemistry, The Central Science , 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten. Ch4 Hmwk # 7, 8, 11, 15, 19, 23, 25, 27, 29, 31, 37, 39, 41, 45, 47 , 51, 53, 59, 63, 67, 69, 75, 96. Chapter 4 Aqueous Reactions and Solution Stoichiometry. John D. Bookstaver

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chapter 4 aqueous reactions and solution stoichiometry

Chemistry, The Central Science, 10th edition

Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten

Ch4 Hmwk # 7, 8, 11, 15, 19, 23, 25, 27, 29, 31, 37, 39, 41, 45, 47, 51, 53, 59, 63, 67, 69, 75, 96

Chapter 4Aqueous Reactions and Solution Stoichiometry

John D. Bookstaver

St. Charles Community College

St. Peters, MO

 2006, Prentice Hall, Inc.

aqueous reactions and solution stoichiometry
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?
solutions
Solutions:
  • Homogeneous mixtures of two or more pure substances.
  • The solvent is present in greatest abundance.
  • All other substances are solutes.
dissociation
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.
electrolytes
Electrolytes
  • Substances that dissociate into ions when dissolved in water. Example: NaCl
  • Anonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so. Example: C12H22O11

Notice, solubility does not imply that something is or is not an electrolyte.

electrolytes and nonelectrolytes
Electrolytes and Nonelectrolytes

Soluble ionic compounds tend to be electrolytes.

electrolytes and nonelectrolytes1
Electrolytes and Nonelectrolytes

Molecular compounds tend to be nonelectrolytes, except for acids and bases.

slide8

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: MgCl2 , KCl, or K2SO4. Which solution does it best represent?

slide9

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: MgCl2 , KCl, or K2SO4. 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 K2SO4.

Check: Notice that the total net charge in the diagram is zero, as it must be if it is to represent an ionic substance.

electrolytes1
Electrolytes
  • A strong electrolyte dissociates completely when dissolved in water.
  • A weak electrolyte only dissociates partially when dissolved in water.
strong electrolytes are1
Strong Electrolytes Are…
  • Strong acids
  • Strong bases
strong electrolytes are2
Strong Electrolytes Are…
  • Strong acids
  • Strong bases
  • Soluble ionic salts
precipitation 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.

metathesis exchange reactions a k a double replacement rxns1
Metathesis comes from a Greek word that means “to transpose”

It appears the ions in the reactant compounds exchange, or transpose, ions

AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)

Metathesis (Exchange) Reactions a.k.a. Double Replacement Rxns
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

AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)

Metathesis (Exchange) Reactions
slide19

AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)

How did we know that silver chloride was a solid???

We checked the solubility table.

predict the products of the following reactions
Predict the products of the following reactions
  • BaCl2(aq) + K2SO4(aq)
  • Fe2(SO4)3(aq) + LiOH (aq)
  • Mg(NO3)2(aq) + CaS (aq)
  • NaCl (aq) + KNO3(aq)
predict the products of the following reactions1
Predict the products of the following reactions
  • BaCl2(aq) + K2SO4(aq)
  • → BaSO4(s) + 2KCl (aq)
  • Fe2(SO4)3(aq) + 6LiOH (aq)
  • → 2Fe(OH)3 (s) + 3Li2SO4 (aq)
  • Mg(NO3)2(aq) + CaS (aq)
  • → MgS (s) + Ca(NO3)2 (aq)
  • NaCl (aq) + KNO3(aq)
  • → NaNO3(aq) + KCl (aq) or NR
solution chemistry
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.
molecular equation
The molecular equation lists the reactants and products in their molecular form.

AgNO3 (aq) + KCl(aq) AgCl(s) + KNO3 (aq)

Molecular Equation
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) + NO3- (aq) + K+ (aq) + Cl- (aq) 

AgCl(s) + K+(aq) + NO3- (aq)

Ionic Equation
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) + NO3-(aq) + K+(aq) + Cl-(aq)

AgCl(s) + K+(aq) + NO3-(aq)

Net Ionic Equation
net ionic equation1
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) AgCl(s)

Net Ionic Equation
net ionic equation2
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) + NO3-(aq) + K+(aq) + Cl-(aq)

AgCl(s) + K+(aq) + NO3-(aq)

Net Ionic Equation
writing net ionic equations
Writing Net Ionic Equations
  • Write a balanced molecular equation.
  • Dissociate all strong electrolytes.
  • Cross out anything that remains unchanged from the left side to the right side of the equation.
  • Write the net ionic equation with the species that remain.
writing net ionic equations write the net ionic equation for each reaction
Writing Net Ionic Equations Write the net ionic equation for each reaction
  • Pb(NO3)2(aq) + KI (aq)
  • Li2S (aq) + BaBr2(aq)
  • NH4Cl (aq) + Sr(OH)2(aq)
writing net ionic equations write the net ionic equation for each reaction1
Writing Net Ionic Equations Write the net ionic equation for each reaction
  • Pb(NO3)2(aq) + 2KI (aq)
  • → PbI2(s) + 2K(NO3) (aq)

Pb2+ + 2I-→ PbI2(s)

  • Li2S (aq) + BaBr2(aq)
  • → LiBr (aq) + BaS (aq)

2Li+(aq) + S-2(aq) + Ba2+ (aq) + 2Br-(aq) → 2Li+(aq) + 2Br-(aq) + Ba2+ (aq) + S-2(aq)

Notice ….all spectator ions. They all cancel and therefore, no reaction occurs.

  • 2NH4Cl (aq) + Sr(OH)2(aq)
  • → SrCl2 (aq) + 2NH4OH (aq)

2NH4+(aq) + 2Cl-(aq) + Sr2+(aq) + 2OH-(aq) → Sr2+(aq) + 2Cl-(aq) + 2NH4+(aq) + 2OH-(aq)

Notice ….all spectator ions. They all cancel and therefore, no reaction occurs.

acids
Acids:
  • Substances that increase the concentration of H+ when dissolved in water (Arrhenius).
  • Proton donors (Brønsted–Lowry).
acids1
Acids

There are only seven strong acids:

  • Hydrochloric (HCl)
  • Hydrobromic (HBr)
  • Hydroiodic (HI)
  • Nitric (HNO3)
  • Sulfuric (H2SO4)
  • Chloric (HClO3)
  • Perchloric (HClO4)

These substances are consider strong acids because they do not just dissolve in water, they will completely dissociate.

bases
Bases:
  • Substances that increase the concentration of OH− when dissolved in water (Arrhenius).
  • Proton acceptors (Brønsted–Lowry).
bases1
Bases

The strong bases are the soluble salts of hydroxide ion:

  • Alkali metals
  • Calcium
  • Strontium
  • Barium
acid base reactions
Acid-Base Reactions

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

neutralization reactions
Generally, when solutions of an acid and a base are combined, the products are a salt and water.

HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)

Neutralization Reactions
neutralization reactions1
When a strong acid reacts with a strong base, the net ionic equation is…

HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)

H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH-(aq)

Na+ (aq)+ Cl- (aq)+ H2O (l)

Neutralization Reactions
neutralization reactions2
When a strong acid reacts with a strong base, the net ionic equation is…

HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)

H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH-(aq)

Na+ (aq)+ Cl- (aq)+ H2O (l)

H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH- (aq)

Na+ (aq) + Cl- (aq) + H2O (l)

Neutralization Reactions

H+ (aq) + OH- (aq) → H2O (l)

neutralization reactions what does this have to do with you
Neutralization ReactionsWhat does this have to do with you???

What happens when you have a stomach ache?

What do you do about it?

Why?

neutralization reactions what does this have to do with you1
Neutralization ReactionsWhat 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)→ Mg2+(aq) + H2O (l)

neutralization reactions3
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?

gas forming reactions
These metathesis reactions do not give the product expected.

The expected product decomposes to give a gaseous product (CO2 or SO2).

CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)

NaHCO3 (aq) + HBr (aq) NaBr (aq)+ CO2 (g) + H2O (l)

SrSO3 (s) + 2 HI(aq) SrI2 (aq) + SO2 (g) + H2O (l)

Gas-Forming Reactions
gas forming reactions1
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:

Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) + H2S (g)

Gas-Forming Reactions
a carbonated beverage is another example
A Carbonated Beverage is Another Example

How is a beverage carbonated?

What happens to the dissolved gas?

H2O (l) + CO2(g)↔ H2CO3(aq)

H2O (l) + CO2(g)↔ 2H+ (aq) + CO3-2(aq)

oxidation reduction 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)
oxidation reduction reactions1
Oxidation-Reduction Reactions

One cannot occur without the other.

oxidation numbers
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.

oxidation numbers1
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.
oxidation numbers2
Oxidation Numbers
  • Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
    • Oxygen has an oxidation number of −2, except in the peroxide ion in which it has an oxidation number of −1.
    • Hydrogen is −1 when bonded to a metal, +1 when bonded to a nonmetal.
oxidation numbers3
Oxidation Numbers
  • Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
    • Fluorine always has an oxidation number of −1.
    • The other halogens have an oxidation number of −1 when they are negative; they can have positive oxidation numbers, however, most notably in oxyanions.
oxidation numbers4
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.
oxidation numbers find the oxidation numbers for each of the following species
Oxidation NumbersFind the oxidation numbers for each of the following species.
  • CO32-
  • H2S
  • S8
  • SCl2
  • SO42-
  • Cr2O72-
slide54
CO32-
  • C = +4 and O = -2
  • H2S
  • H = +1 and S = -2
  • S8
  • S = 0
  • SCl2
  • S = +2 and Cl = -1
  • SO42-
  • S = +6 and O = -2
  • Cr2O72-
  • Cr = +6 and O = -2
examine each reaction below and identify the oxidized and reduced reagents
Examine each Reaction below and Identify the oxidized and reduced reagents
  • 2K (s) + 2H2O (l)→ 2KOH (aq) + H2(g)
  • Fe2O3(s) + 2Al (s) → 2Fe (l) + Al2O3(s)
  • Si (s) + 2Cl2(g) → SiCl4(l)
examine each reaction below and identify the oxidized and reduced agents
Examine each Reaction below and Identify the oxidized and reduced agents
  • 2K (s) + 2H2O (l)→ 2KOH (aq) + H2(g)

K (s) → K+(aq), it was oxidized; Hydrogen was reduced in water to form hydrogen gas.

  • Fe2O3(s) + 2Al (s) → 2Fe (l) + Al2O3(s)

Aluminum metal is oxidized; iron is reduced

  • Si (s) + 2Cl2(g) → SiCl4(l)

Si is oxidized while Cl is reduced

which three of the following reactions are red ox what is oxidized and what is reduced
Which three of the following reactions are Red-Ox? What is oxidized and what is reduced?

Zn (s) + 2NO3-(aq) + 4H+(aq)→ Zn+2(aq) + 2NO2 (g) + 2H2O (l)

Zn(OH)2 (s) + H2SO4 (aq) → ZnSO4(aq) + 2H2O (l)

Ca (s) + 2H2O (l) → Ca(OH)2(s) + H2(g)

4Fe(OH)2(s) + 2H2O (l) + O2(g) → 4Fe(OH)3(aq)

which three of the following reactions are red ox what is oxidized and what is reduced1
Which three of the following reactions are Red-Ox? What is oxidized and what is reduced?

Zn (s) + 2NO3-(aq) + 4H+(aq)→ Zn+2(aq) + 2NO2 (g) + 2H2O (l)

Red-ox: zinc is oxidized, nitrogen is reduced

Zn(OH)2 (s) + H2SO4 (aq) → ZnSO4(aq) + 2H2O (l)

Not Red-ox

Ca (s) + 2H2O (l) → Ca(OH)2(s) + H2(g)

Red-ox: calcium is oxidized, hydrogen is reduced

4Fe(OH)2(s) + 2H2O (l) + O2(g) → 4Fe(OH)3(aq)

Red-ox: Iron is oxdized, oxygen is reduced

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

In this reaction,

silver ions oxidize

copper metal.

Cu (s) + 2 Ag+ (aq) Cu2+ (aq) + 2 Ag (s)

displacement reactions1
Displacement Reactions

The reverse reaction,

however, does not

occur.

Cu2+ (aq) + 2 Ag (s)  Cu (s) + 2 Ag+ (aq)

x

slide63

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(NO3)2(aq)
slide64
2Al(s) + 6HBr (aq)

→ 2AlBr3(aq) + 3H2(g)

2Al (s) + 6H+(aq) → 2Al3+(aq) + 3H2(g)

Aluminum is oxidized and Hydrogen is reduced.

  • Fe(s) + KI (aq)

No Reaction

  • Zn (s) + Ni(NO3)2(aq)

→ Zn(NO3)2(aq) + Ni (s)

Zn (s) + Ni2+(aq) → Zn2+(aq) + Ni (s)

Zinc is oxidized and Nickel is reduced.

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

Molarity
mixing a solution
Mixing a Solution
  • How many grams of silver nitrate are required to make 100 mL of a 0.5 M solution?
  • How many grams of NaOH are required to make 50 mL of an 8.2 M solution?
mixing a solution1
Mixing a Solution
  • How many grams of silver nitrate are required to make 100 mL of a 0.5 M solution?
  • 9 grams
  • How many grams of NaOH are required to make 50.0 mL of an 8.2 M solution?
  • 16 grams
dilution
Dilution

M1V1 = M2V2

dilution1
Dilution
  • You have 1L of a 1.00 M stock solution of hydrochloric acid. You need to make 500 mL of a 0.20M solution. How much of the stock solution is needed?
  • You need to make 100 mL of 0.50 M nitric acid. The storage bottle reads 6.0M. How much of the 6.0M nitric acid will you need?
dilution2
Dilution
  • You have 1L of a 1.00 M stock solution of hydrochloric acid. You need to make 500 mL of a 0.20M solution. How much of the stock solution is needed?

100. mL or 0.100 L

  • You need to make 100 mL of 0.50 M nitric acid. The storage bottle reads 6.0M. How much of the 6.0M nitric acid will you need?

8.3 mL

using molarities in stoichiometric calculations
Using Molarities inStoichiometric Calculations

How many grams of Ca(OH)2 are needed to neutralize 20.0 mL of a 0.150 M H2SO4 solution?

0.222 g (see board for work)

using molarities in stoichiometric calculations1
Using Molarities inStoichiometric Calculations

How many liters of 0.500 M HCl are needed to react completely with 0.100 mol Pb(NO3)2, forming the precipitate PbCl2?

0.400L (see board for work)

titration
Titration

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

titration example
Titration Example

A 1.034-g sample of impure oxalic acid (H2C2O4) is dissolved in water and an acid-base indicator is added. The sample required 34.47 mL of 0.485 M NaOH to reach the equivalence point. What is the mass of oxalic acid and what is its mass percent in the sample?

0.752 g H2C2O4 and 72.7% H2C2O4

(see board for work)

titration2
Titration

A 0.263-g sample of sodium carbonate requires 28.35 mL of aqueous HCl for titration to the equivalence point. What is the molarity of the HCl?

0.175 M HCl

slide77

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