CH 4 AP

Reactions in

Aqueous Solutions

Water Aqueous means dissolved in H2O Moderates the Earth’s temperature because

of high specific heat H-bonds cause strong cohesive and adhesive

properties Polar, therefore dissolves many substances

both ionic and polar Solutions: with solvent (dissolving medium)

and solute (being dissolved)

Electrolyte is a solution which will conduct electricity (solute makes ions in solution allow the flow of e-) Ion Dissociation Solvated is when an ionic compound dissolves in H2O and the ions become surrounded by the H2O molecules.

Non-electrolyte is a solutions which will NOT conduct electricity (no ions present to permit flow of e-)

Strong Electrolytes are made with substances which completely ionize in H2O, they have large equilibrium constants.

1. Soluble salts NaCl(s) Na+1

(aq) + Cl-1(aq)

2. Strong acids HCl H+

(aq) + Cl-1(aq)

Arrhenius acids product H+1 when dissolved in H2O

3. Strong bases NaOH(s) Na+1

(aq) + OH-1(aq)

Weak electrolytes exhibit small amounts of

ionization when dissolved in H2O, have small

equilibrium constants.

1. Weak acids HC2H3O2(aq) H+1

(aq) + C2H3O2-1

(aq)

2. Weak bases NH3 (aq) + H2O (L) NH4

+1(aq) + OH-1

(aq)

Non-electrolytes produce NO ions upon

dissolving in H2O

Writing half reactions

Ag Ag+1

Ba Ba+2

F F-1

S S-2

Fe+2 Fe+3

Do you know the subatomic particles?

e- p+ e- p+

Ag Ag+1

Ba Ba+2

F F-1

S S-2

Fe+2 Fe+3

Do you remember how to write formulas? Oxide

O-2

Iodide

I-1

Sulfate

SO4-2

Phosphate

PO4-3

Cyanide

CN-1

Hydrogen

H+1

Barium

Ba+2

Chromium

Cr+3

Molarity (M): concentration of solution expressed as moles of solute per volume of solution in liters.

Molarity = moles/liter

Calculate the molarity of a solution prepared by dissolving 17.5 g of solid NaOH in enough H2O to make 1.75 L of

solution.

Volumetric flask

To use:

Fill ½ full of distilled H2O

Add solute

Cap and invert to mix

Add H2O until close to line on neck

Cap and invert to mix

Carefully, add H2O until meniscus is at the line on neck

Calculate the concentration of each type of ion in the following:

0.50 M AlCl3

2 M (NH4)2CO3

Calculate the moles of Cl-1 ions in 1.3 L of 0.05 M MgCl2.

Typical blood serum is about 0.14 M NaCl. What volume of blood contains 1.0 mg NaCl?

How many grams of AgCl must be used to make 75 mL of

0.1 M AgCl solution?

Dilutions: moles = moles M1 V1 = M2 V2

What volume of 0.25 M K2CrO4 must be used to prepare 1.0 L of 0.05 M K2CrO4?

What volume of 12.0 M HCl must be used to prepare 2.5 L of 0.1 M HCl?

Types of Chemical Reactions

1. Precipitation Reaction is when 2 solutions are mixed resulting in an insoluble substance.

(Insoluble & slightly soluble are used interchangeably here. Any substance that is less soluble than .01 mol

/L is considered insoluble.)

When writing the formula for the precipitate:

a. Precipitate has a net charge of zero

b. Contains a cation (+ ion) and an anion (- ion)

c. Write cation first, anion second

Solubility Rules Soluble: the following are always soluble

1. Nitrates (NO3-1) and Acetates (C2H3O2

-1)

2. Alkali Metals (Li+1 Na+1 K+1 Cs+1 Rb+1) and

Ammonium (NH4+1)

3. Halides (Cl-1 Br-1 I-1) (except with Ag+1 Pb+2 Hg2

+2 are insoluble)

4. Sulfates (SO4-2)

(except with Ba+2 Pb+2 Hg2+2 Sr+2 Ca+2 are insoluble)

Mostly Insoluble

1. Hydroxides (OH-1) (except with Alkali metals or ammonium are soluble) (except with Ca+2 Sr+2 Ba+2 are slightly soluble) 2. Sulfides (S-2) (except with Alkali metals, ammonium are soluble ) (except with Alkali Earth metals Be+2 Mg+2 Ca+2 Sr+2 Ba+2 are slightly soluble) 3. Carbonates (CO3

-2) and Phosphates (PO4-3) are slightly

soluble (except with alkali metals and ammonium are soluble) Chromates are insoluble except with alkali metals or ammonium

Write the net ionic equation for all precipitates that can be made mixing the following chemicals:

Ba(NO3)2 KCl Na2CO3 Ag2SO4 Mg(C2H3O2)2 NaOH

Writing chemical equations Formula equation: shows everything involved K2CrO4 (aq) + Ba(NO3)2 (aq) BaCrO4 (s) + 2 KNO3 (aq)

Complete ionic equation: includes all spectator ions, those

ions which are not involved in the chemical reaction 2K+1

(aq) + CrO4+2

(aq) + Ba+2(aq) + 2NO3

-1(aq) BaCrO4 (s) + 2 K+1

(aq) + 2 NO3-1

(aq)

Net ionic equation: only shows chemicals involved in the reaction, no spectator ions Ba+2

(aq) + CrO4-2

(aq) BaCrO4 (s)

All of the above are the same reaction shown in different

types of equations.

Try writing all 3 types of equations for: Aqueous potassium chloride is added to aqueous silver nitrate

Aqueous potassium hydroxide is mixed with aqueous iron(III) nitrate

To calculate ion concentrations after reactions

1. Identify species present as reactants and products (the complete ionic equation)

2. Change to moles

3. Find the Limiting reactant

4. ICE chart

I = initial concentration

C = change in concentration

E = ending concentration

5. Use stoichiometric relations

6. Calculate moles of ions for any soluble chemicals (or excess chemicals)

7. Change to Molarity using total volume

Calculate the concentrations of all ions and mass of precipitate after 100 mL of 1.0 M Mg(NO3)2 reacts with 200 mL of 1.0 M NaOH.

Mg(NO3)2(aq) + 2 NaOH

I

C

E

1.0 L of 0.1 M Ba(NO3)2 is mixed with 500 mL of 0.1 M Na2SO4. What are the final concentrations of ions in solution and mass of precipitate?

Ba(NO3)2 (aq) + Na2SO4 (aq)

I

C

E

How many grams of silver chloride can be produced by the reaction of 100 mL of .20 M silver nitrate with 100 mL of .15 M calcium chloride. Calculate the concentration of all ion at the end of the reaction.

Reaction Type 2 Acid – Base Reaction

Theories: Acid Base

Arrhenius H+ OH-

Bronsted – Lowry proton donor proton acceptor

(proton = H+ , a hydrogen without and e-)

Lewis e- pair acceptor e- pair donor

Strong:ionize 100 % Need to memorize strong Acids & Bases both HCl & NaOH strong: H+1 + Cl-1 + Na+1 + OH-1

spectator ions

Net ionic equation: H+1 + OH-1 H2O(L)

Weak: ionize some weak acid (HC2H3O2 stays mainly as molecule) & strong base(KOH ionizes 100 %) Net ionic equation: HC2H3O2 + OH- H2O + C2H3O2

- Non – electrolyte: ionize 0% We will start with only strong acids and bases, therefore ionize 100%

strong acid + strong base salt + water HA + BOH BA + H2O (net) H+ + OH- H2O Neutralization Reactions with gas formation: (Acid) 2 H+1 + S-2 H2S(g)

H+1 + HCO3

-1 H2CO3

H2CO3 H2O + CO2(g)

When calculating acid base equations, remember that moles A = moles B MA VA = MB VB

What volume of 0.100 M HCl solution is needed to neutralize 25.0 mL of 0.35 M NaOH?

moles A = moles B MA VA = MB VB

This works using M x Liters = moles

mole/Liter = M

This also works using

M x milliliters = millimoles

millimole/milliliter = M

28.0 mL of 0.25 M HNO3 reacts with 53.0 mL of 0.32 M KOH. Calculate the amount of H2O formed in the resulting reaction. What concentration of H+1 or OH-1 is in excess?

KOH(aq) + HNO3(aq)

I

C

E

Volumetric Analysis: Titration delivers a given amount of known concentration (titrant) to a given amount of unknown concentration (analyte). Equivalence point is the stoichiometric point when the moles = moles. An indicator chemical is added which changes color at the equivalence point (end point). Standardizing is using a solution of a very stable chemical to determine the M of an unknown.

A student standardizes an NaOH solution using Potassium Hydrogen Phthalate (KHC8H4O4 KHP) (m=204.22). The student dissolves 1.3009 g KHP in H2O, adds phenolphthalein and titrates with 41.20 mL NaOH of unknown concentration. Find the concentration. H+1 + OH-1 H2O HC8H4O4

-1 + OH-1 H2O + C8H4O4-2

Reaction Types #3 Oxidation – Reduction (Redox) A reaction in which one or more e- are transferred.

Oxidation Reduction

Increase in os

therefore Reducing Agent

Loss of e-

Gain of oxygen

Loss of hydrogen

Decrease in os

therefore Oxidizing Agent

Gain of e-

Loss of oxygen

Gain of hydrogen

0 Oxidation Reduction

Oxidation State (o.s.) (oxidation number)

*Is an imaginary charge.

*It is a way to arbitrarily assign e- to atoms especially in covalent bonds

*The e- are often not shared equally, one atom may have a stronger e- affinity or attraction.

Rules for assigning o.s. Whenever 2 rules appear to contradict one another, follow the rule that appears higher on the list!

1. The oxidation state (os) of an atom in the free (uncombined) element is zero (o).

2. The total of the os of all the atoms in a molecule is zero (o). For an ion, the total is equal to the charge on the ion.

3. In their compounds, Alkali metals (Li, Na, K, Rb, Cs, Fr) have os = +1 Alkali Earth metals (Be, Mg, Ca, Sr, Ba, Ra) have os = +2 4. In their compounds, Hydrogen has os = +1

Fluorine has os = -1 5. In it’s compounds, Oxygen has os = -2 6. In 2 element compounds, Halogens (Cl, Br, I) have os = -1 (O, S, Se, Te, Po) have os = -2 (N, P, As, Sb, Bi) have os = -3

Determine the os for the following underlined elements.

S8

Cr2O7-2

Cl2O

KO2

S2O3-2

KMnO4

H2CO3

Write the formulas for the oxides with the following charges.

Cr+3

Cr+4

Cr+6

N+1

N+2

N+3

N+4

N+5

Activity Series of Metals see page 144

A list of metals arranged in order of decreasing ease of oxidation.

The higher on the chart, the more active the metal.

Any metal on the list can be oxidized by the ions of elements below it.

Will an aqueous solution of iron (II) chloride oxidize Mg(s)

Metal Activity Series – Any metal on the list can be oxidized by the ions of elements below it.