Chapter 4

Types of Chemical Reactions and Solution

Stoichiometry

Parts of solutions

Solution – homogeneous mixtureSolute – part that dissolvesSolvent – causes the dissolvingSoluble – can be dissolvedMiscible – liquids dissolve in each

other

Saturation of SolutionsA solution that contains the maximum

amount of solute dissolved under existing conditions is saturated.

A solution that contains less solute than a saturated solution under existing conditions is unsaturated.

A solution that holds more solute than a saturated solution under the same conditions is supersaturated.

Aqueous SolutionsDissolved in waterWater is a polar moleculeThe oxygen atoms have a partial

negative chargeThe hydrogen atoms have a partial

positive chargeThe angle is 105o

HydrationThe process of breaking apart ions

of a salt.The “+” end of water attracts the

anionThe “-” end of water attracts the

cation

SolubilityThe ability to dissolve in a given

amount of waterUsually g/100mLVaries greatlyDepends upon ion attractionWill dissolve nonionic substances if

they have polar bonds

ElectrolytesElectrical current through a

substanceIons that are dissolved can moveSolutions are classified three ways

Types of SolutionsStrong electrolytes –Completely ionized

when dissolved in water many ions – conduct wellWeak electrolytes – partially fall apart

into ions few ions- conduct electricity slightlyNon-electrolytes – don’t fall apart no ions – don’t conduct electricity

Types of solutions continuedAcids – form H+ ion when dissolvedStrong acids fall apart completely H2SO4 HNO3 HCl HBr HI HClO4

Weak acids – do not dissociate completely

Bases – form OH- when dissolvedStrong bases – KOH NaOH

DissociationAcids

HCl H+ (aq) + Cl-(aq) HNO3 H+(aq) + NO3

- (aq) H2SO4 H+ (aq) + HSO4

- (aq)

Strong bases NaOH Na+ (aq) + OH- (aq)

KOH K+ (aq) + OH-(aq)

NonelectrolytesDissolve in water but do not

produce any ionsExample is ethanol (C2H5OH) molecules disperse in the water

but doesn’t conduct electricity

Composition of SolutionsConcentration

1. Molarity (M) – moles of solute per volume of solution in liters

2. M = moles of solute liters of solution

Preparation of Molar SolutionsCalculate the molarity of a solution prepared by dissolving 1.56 g of gaseous HCl in enough water to make 26.8 mL of solution.

1.56 g HCl

1

1 mole HCl 36.5 g HCl = 0.0427 mole HCl

26.8 mL 1

1L 1000 mL

= .0268 L

M = 0.0427 mole HCl .0268 L

= 1.60 M HCl

Concentrations of Ions Give the concentration of each type of ion in 0.50 M

Co(NO3)2Co(NO3)2 (s)

Co+2 (aq) + 2NO3- (aq)

Co+2 1 x 0.50 M = 0.50 M Co+2

NO3-

2 x 0.50 M = 1.0 M NO3

-

Calculate the number of moles of Cl- ions in 1.75 L of 1.0 x 10-3 M ZnCl2.

ZnCl2 Zn+2 (aq) + 2Cl- (aq)

2 x 1.0 x 10-3 = 2.0 x 10-3 M Cl-

1.75 L 2.0 x 10-3 mole Cl- L

= 3.5 x 10-3 mole Cl-

Standard solution – a solution where the concentration is accurately known

How much solid K2Cr2O7must by weighted out to make a solution? A chemist needs 1.00 L of an aqueous 0.200 M K2Cr2O7 solution.

Dilution1. Water is added to achieve a particular M2. Moles of solute after = moles of solute

before3. M1V1=M2V2

What volume of 16 M sulfuric acid must be used to prepare 1.5 L of a 0.10 M H2SO4 solution?

Types of Solution ReactionsPrecipitation Reactions

1. A solid forms from two solutions

2. Precipitate – the insoluble solid

KNO3 (aq) + BaCl2 (aq)

Three Types of Equations Used to Describe Reactions in a Solution

The formula equation gives the overall reaction.

The complete ionic equation represents as ions all the reactants and products that are strong electrolytes.

The net ionic equation includes only those ions that undergo a change.

Write the formula equation, complete ionic equation, and the net ionic equation for

KCl (aq) + AgNO3 (aq)

Stoichiometry of Precipitation Reactions

Calculate the mass of solid NaCl that must be added to 1.50 L of a 0.100 M AgNO3 solution to precipitate all the Ag+ ions in the form of AgCl.

When aqueous solutions of Na2SO4 and Pb(NO3)2 are mixed, PbSO4 formed when 1.25 L of 0.0500 M Pb(NO3)2 and 2.00 L of 0.0250 M Na2SO4 are mixed.

Acid-Base ReactionsAcid is a proton donor (H+)Base is a proton acceptor usually OH— accepts a H+

H+(aq) + OH− (aq)

Cations are surrounded and bound by water molecules protons are also solvated by water molecules

Two ways to show this

1. H+ (aq)2. H3O+ (aq) – hydronium ion

Types of acid donorsMonoprotic HCl, HNO3 donates ____ H+

Diprotic H2SO4 donates ____ H+

Triprotic H3PO4 donates ____ H+

Neutralization ReactionsWhat volume of a 0.100 M HCl solution is

needed to neutralize 25.0 mL of 0.350 M NaOH? HCl (aq) + NaOH (aq) NaCl(aq) + H2O (l)

H+(aq) + OH−(aq) H2O (l)

.0250 L 0.350 mole OH− =

L NaOH

Acid-Base TitrationsVolumetric analysis

Process of determining the amount of a substance by titration

Titration Process of delivering solutions to one anotherEquivalence point (stoichiometric point) Point at which the titration has occurred Endpoint

Point at which the indicator changes color

What volume of 0.812 M HCl, in milliliters, is required to titrate 1.33 g of NaOH to the

equivalence point?

Oxidation-Reduction ReactionsElectrons are transferredSpontaneous redox rxns can transfer

energy Electrons (electricity) Heat

LEO the lion says GER

Lose Electrons = OxidationGain Electrons = Reduction

Redox Reactions Examples:0 0 +1 --1

2Na + Cl2 2NaClEach sodium atom loses one electron oxidation

Each chlorine atom gains one electron: 0 -1 Cl + e__ Cl

reduction

Rules for Assigning Oxidation Numbers Rules 1 & 2

1. The oxidation number of any uncombined element is zero

2. The oxidation number of a monatomic ion equals its charge

3. The oxidation number of oxygen in compounds is -2

4. The oxidation number of hydrogen in compounds is +1

5. The sum of the oxidation numbers in the formula of a compound is 0.

6. The sum of the oxidation numbers in the formula of a polyatomic ion is equal to its charge

ex. NO3—

SO42—

Reducing Agents and Oxidizing Agents

The substance reduced is the oxidizing agentThe substance oxidized is the reducing agent

0 +1 Na Na + e --

Sodium is oxidized – it is the reducing agent0 -- 1

Cl + e-- Cl

Chlorine is reduced – it is the oxidizing agent

Oxidation-Number Changes in reactions

Can you identify what is being oxidized and what is being reduced?

2AgNO3 (aq) + Cu (s) Cu(NO3)2(aq) + 2Ag (s)

The oxidation number of Ag decreases from +1 to 0 (reduction), copper’s oxidation number increase from 0 to +2 (oxidation)

Balancing Redox EquationsLook at the reaction between solid copper and

silver ions in aqueous solution:Cu (s) + Ag+ (aq) Ag (s) + Cu+2 (aq)

Cu + Ag+ Ag + Cu+2

1 e--

gained

0 +1 0 +2

2 e- lost

Ultimately must have equal number of electrons gained and lost

Cu (s) + 2 Ag+ (aq) 2 Ag (s) + Cu+2 (aq)

Try balancing:

H+ (aq) + Cl_ (aq) + Sn (s) + NO3- SnCl6 (aq) + NO2 (g)+ H2O

(l)