MicrosoftPowerPoint-AqueousReactionsnoteswithoutcomesv2.pdf

Any given substance at a certain

temperature can dissolve to only a certain

maximum in a given solvent.

A saturated solution contains the maximum

amount of solute that it can hold at a given

amount of solute that it can hold at a given

temperature. This maximum amount is

known as a substance's solubility and is a

characteristic property of that substance.

Substances that contain less than the

If a saturated solution is heated, more solute will

dissolve. If it is then slowly cooled without being

disturbed it will contain more solute than it can

normally hold at that temperature. Such solutions

are said to be supersaturated

are said to be supersaturated

When liquids dissolve in liquids, different

descriptors are used. Two liquids are said to be

miscible if they can dissolve in each other

(eg. methanol and water). Liquids that are

A solution is a homogeneous mixture of

substances. If there is much more of one substance than any others, then that substance is referred to as

the solvent, all other substances in the mixture are

called solutes.

An aqueous solution is one whose solvent is water.

An aqueous solution is one whose solvent is water.

Many properties of an aqueous solution are similar

to the properties of water1 (e.g. density, viscosity,

melting point, boiling point). Most properties will be slightly changed by the presence of solutes, and some

The properties of the solutes are greatly changed and

we define the aqueous state as distinct from the solid, liquid and gaseous states of matter. The solute

molecules no longer interact with each other, as they are spread out in the solution.

The solutes are solvated by water molecules. That is,

they are surrounded by solvent molecules, usually with some degree of order, imposed by the polarity of the some degree of order, imposed by the polarity of the water molecules and the polarity or charge of the

Electrolytes

Some solutes remain molecular (e.g. sugar, ethanol). In

order to be soluble in water they must be somewhat polar molecules. These solutes have no effect on the electrical properties of the solution and are classified

as non-electrolytes.

Some solutes are dissociated into ions when they Some solutes are dissociated into ions when they

dissolve in water, (e.g. NaCl, HBr).

These solutes increase the electrical conductivity of

water and are classified as electrolytes. Ions increase the conductivity because electrical current is

carried by the highly mobile and electrically charged

We can further subdivide electrolytes into strong and weak. Strong Electrolytes: completely dissociate into ions

when in aqueous solution.

The resulting solution is a strong conductor of electricity. Weak Electrolytes: partially dissociate into ions when Weak Electrolytes: partially dissociate into ions when

in aqueous solution.

The resulting solution is a weak conductor of electricity. Non-Electrolytes: do not dissociate into ions when in

aqueous solution.

1. All ionic compounds are

strong

electrolytes.

2. Some acids and bases are strong

electrolytes; many others are

weak.

electrolytes; many others are

weak.

3. Most other molecules are

Negative ions Positive Ions Solubility

essentially all alkali ions (Li+_{, Na}+_{, K}+_{, Rb}+_{, Cs}+_{) soluble}

essentially all hydrogen ion H+ _soluble

essentially all ammonium ion (NH4+_{) soluble}

nitrate, NO₃- _{essentially all soluble}

Solubility Chart

acetate, CH₃COO- _{essentially all (EXCEPT Ag}+_{) soluble}

chloride, Cl- _{bromide, Br}

-iodide, I

-Ag+_,Pb2+_,H

g22+,Cu+,Tl+ low solubility

all others soluble

sulfate, S0₄2- _{2+ 2+ 2+ 2+ 2+}

Ca , Sr , Ba , Pb , Ra

low solubility

Negative ions Positive Ions Solubility

sulfide, S

2-alkali ions, H+

(aq) , NH4+, Be2+,

Mg2+_,Ca2+_,Sr 2+ _Ba2+_,Ra2+

soluble

all others low solubility hydroxide, OH~ _{Alkali ions, H}+

(aq) , NH4+,

Sr 2+ _Ba2+_,Ra2+_Tl+

soluble

all others low solubility

phosphate, PO4

3-carbonate, CO₃2-_sulfite,

SO₃

2-alkali ions, H+

(aq) , NH4+, soluble

all others low solubility

chromate, CrO42- _Ba2+_,Sr2+_,Pb2+_,Ag+ _{low solubility}

Acid-Base Reactions

Some common acids and bases in your

kitchen or bathroom are: aspirin,

vinegar, citric

acid, bleach, ammonia, and baking soda.

What makes a substance an acid or a

What makes a substance an acid or a

base?

Earliest classifications were based on

Taste sour (don’t try this at home).

Conduct electricity.

Some are strong, others are weak electrolytes.

React with metals to form hydrogen gas.

14

Change indicators (blue litmus to red).

React with acids to form water and a salt. Taste bitter.

Feel slippery (don’t try this either). Can be strong or weak electrolytes.

15

An acid is a chemical that produces hydrogen ions (H1+_{) when dissolved in water}

Thus, general formula = HX, where X is a monatomic or polyatomic anion

HCl_(g) named hydrogen chloride

16

HCl_(g) named hydrogen chloride HCl_(aq) is named as an acid

Naming Acid

Hydrogen _______ide becomes hydro____ic

acid

Hydrogen_______ate becomes _________ic

chlor chlor

17

Hydrogen_______ate becomes _________ic

acid

1.

When anion ends with -ide, the acid starts

with

hydro-,

and the stem of the anion has

the suffix

-ic

followed by the word

acid

2. When anion ends with -ite, the anion has the

18

2. When anion ends with -ite, the anion has the

suffix

-ous

, then

acid

A base produces hydroxide ions (OH

1-) when dissolved in water.

Named the same way as any other

ionic compound

19

ionic compound

name the cation, followed by anion

To write the formula: write symbols;

Swedish chemist (1859-1927) - Nobel prize winner in

chemistry (1903)

One of the first chemists to explain the chemical theory

20

Acids produce hydrogen ions (H1+) in aqueous solution.

Bases produce hydroxide ions (OH1-) when dissolved in

water.

HCl H+ _{+ Cl}

-H₂O

H₂O

21 Limited to aqueous solutions.

Only one kind of base (hydroxides)

NH₃ (ammonia) would not be an Arrhenius base.

Some compounds have more than 1 ionizable hydrogen.

HNO₃ nitric acid – monoprotic

H₂SO₄ sulfuric acid - diprotic - 2 H+

22 H₂SO₄ sulfuric acid - diprotic - 2 H

H₃PO₄ phosphoric acid - triprotic - 3 H+

Having more than one ionizable hydrogen does not mean

However, not all compounds that have hydrogen are acids

Also, not all the hydrogen in an acid may be released as ions

NH

or H

O

23

as ions

CH3COOH CH3COO- + H+

only those that have very polar bonds are ionizable - this

Consider HCl

What about CH₄

(methane)?

24

CH₃COOH

(ethanoic acid, or acetic acid) - it has 4

A proton is a positively charged subatomic particle

(no neutrons, no electrons)

A hydrogen atom is 1 proton(+) and 1 electron (-)

25

A hydrogen ion or proton (H

) is a hydrogen atom

that has lost its electron leaving only the proton

Broader definition than Arrhenius

Acid is hydrogen-ion donor (H+ or proton); base is hydrogen-ion

acceptor.

Acids and bases always come in pairs

26

HCl is an acid.

When it dissolves in water, it gives it’s proton to water.

A conjugate base is the remainder of the

original acid, after it donates it’s hydrogen ion

A conjugate acid is the particle formed when

27

A conjugate acid is the particle formed when

the original base gains a hydrogen ion

Indicators are weak acids or bases that have a

General equation is:

HA_(aq) + H₂O_(l) H₃O+_(aq) + A-_(aq)

Acid Base Conjugate acid Conjugate base

28

Acid Base Conjugate acid Conjugate base

NH₃ + H₂O NH₄1+ + OH

HCl + H

HCl + H

O H

O H

O

O

+ Cl

+ Cl

11--acid base c.a. c.b.

acid base c.a. c.b.

Amphoteric

Amphoteric -- acts as acid or base

acts as acid or base

29

Amphoteric

Amphoteric -- acts as acid or base

acts as acid or base

(H

(H

0, HSO

0, HSO

, H

, H

22

PO

PO

) must be able to give a H

) must be able to give a H

Gilbert Lewis focused on the donation or acceptance of

a pair of electrons during a reaction

Lewis Acid - electron deficient

Lewis Base - electron rich

30 Lewis Base - electron rich

Most general of all 3 definitions; acids don’t even need

Several categories of substances can be considered Lewis acids:

Electron Poor

1) positive ions

2) having less than a full octet in the valence shell 3) polar double bonds (one end)

4) expandable valence shells

31

4) expandable valence shells

Several categories of substances can be considered Lewis bases:

Electron Rich

1) negative ions

2) one of more unshared pairs in the valence shell 3) polar double bonds (the other end)

Name the metal and then add hydroxide

OBJECTIVES:

Convert hydrogen-ion concentrations

33

Water ionizes, or falls apart into ions:

H₂O → H1+ + OH

Called the “self ionization” of water

Occurs to a very small extent:

[H1+ _{] = [OH}1-_{] = 1 x 10}-7 _M

34

[H ] = [OH ] = 1 x 10 M

Since they are equal, a neutral solution results from water

K_w = [H1+ ] x [OH1-] = 1 x 10-14

(

H₂O H+ + OH

K_w is constant in every aqueous solution: [H+] x

[OH-] = 1 x 10-14

If [H+] >1x 10-7 then [OH-] < 1x10-7 If [H+] < 1x10-7 then [OH-] > 1x10-7

If we know one,the other can be determined

35

If we know one,the other can be determined

If [H+] > 10-7 , it is acidic and [OH-] < 10-7 If [H+] < 10-7 , it is basic and [OH-] > 10-7

Logarithms are powers of ten.

Know how to use the log buttons on your calculator

definition: pH = -log[H+]

in neutral pH = -log(1 x 10-7) = 7

+ -7

36

in acidic solution [H+] > 10-7

pH < 7 (from 0 to 7 is the acid range)

pOH = -log [OH-]

[H+] x [OH-] = 1 x 10-14 M2

pH + pOH = 14

37

[H

]

10

10

10

10

10

10

10

10

10

Acidic

Neutral

Basic

39

[OH

]

Acidic

Neutral

Basic

Kw = [H₃O+_{] [OH}-_{] = 1 x 10}-14

pH = - log[H₃0+]

[H₃O+] = antilog (-pH)

Acid Equations Ion Product Constant Ion Product Constant

40

pOH = -log [OH-]

pH + pOH = 14

3

[OH-] = antilog (-pOH)

Base Equations

pH Scale Equation

Why measure pH?

Everything from swimming pools,

soil conditions for plants, medical

diagnosis, soaps and shampoos, etc.

41

diagnosis, soaps and shampoos, etc.

Sometimes we can use indicators, other

An indicator is an acid or base that

undergoes dissociation in a known pH

range, and has different colors in solution

(more later in chapter)

42

(more later in chapter)

HIn

H

+ In

Examples: litmus, phenolphthalein,

Although useful, there are limitations to indicators:

usually given for a certain temperature

(25 o_{C), thus may change at different temperatures}

what if the solution already has color? ability of human eye to distinguish colors

A

pH meter

(

simulation

)may give

more definitive results

some are large, others portable

works by measuring the voltage

44

works by measuring the voltage

between two electrodes

Reactions (ionizations/neutralizations) of

strong

acids and bases (acid/base) in water go

to

completion.

HCl (

aq) à H+ (aq) + Cl- (aq)

NaOH (

aq) + HCl (aq) à NaCl (aq) + H2O (l)

Reactions (ionizations/neutralizations) of

weak

Reactions (ionizations/neutralizations) of

weak

acids and bases (acid/base) in water are

reversible and reach an

equilibrium state16.

HF (

aq)

+ (aq) + F- (aq)

OXIDATION AND REDUCTION

Just from the sound of the title, you can infer that oxidation has something to do with oxygen. In fact, the original definition was " to combine with oxygen".

E.g. A burning match… C + O₂→CO

2 + heat

E.g. A burning match… C + O₂→CO

2 + heat

Rusting iron…..Fe + O₂→Rust (iron oxide)

Reduction, therefore, meant to remove O₂.

E.g. Fe₂O₃ + 3C →4Fe + 3CO

E.g. Fe

O

+ 3C

→

4Fe + 3CO

2

Today, the terms

oxidation

and

reduction

have a much broader definition.

To

understand the modern definition of

oxidation and reduction we must first

understand how to define oxidation

understand how to define oxidation

numbers.

Oxidation Numbers

In a binary ionic compound, such as CaO, we

can separate the elements and assign them

definite charges,

e.g. Ca2+O2-, and so we

know how many electrons are transferred in

each

half reaction. For polar covalent compounds,

half reaction. For polar covalent compounds,

e.g. HCl and SO2, each atom does not have

You must learn the rules for assigning oxidation numbers. You should be able to

assign oxidation numbers, and be familiar with the most

common oxidation states of elements up to argon. You should then be able to use changes in oxidation numbers to

identify the atoms oxidized and reduced as well as the oxidizing agent and reducing agent.

Note that the oxidizing and reducing agents may be the same Note that the oxidizing and reducing agents may be the same compound or element.

An atom is oxidized when its oxidation number increases.

(It is the reducing agent.)

An atom is reduced when its oxidation number is

reduced. (It is the oxidizing agent.)