Chem I Unit 8

Acids and Bases

&

Gas Laws

Properties of Acids and Bases

Acids

Taste Sour

Mild solutions feel like water on skin, but sting cuts

Concentrated solutions are corrosive to skin

React vigorously with many metals

Electrolytes

pH < 7

Bases

Taste Bitter

Mild solutions feel smooth, soothing and slippery

Concentrated solutions are corrosive to skin

Do not react with most metals

Electrolytes

pH > 7

Neutralization Reactions

When an acid is added to a base, they neutralize

each other, resulting in a solution that has none of

the distinctive properties of an acid or base

Acid + Base � Salt + Water

HCl + NaOH � NaCl + H2O

H2SO4 + Al(OH)3 � Al2(SO4)3 + H2O

Salt – the neutral product of an acid/base rxn

Write Balanced Chemical Equations

for the following Reactions.

Sulfuric acid and Calcium hydroxide

Hydrobromic acid and Aluminum hydroxide

Phosphoric acid and sodium hydroxide

�Name the salt formed in each reaction.

Properties of Salts

Ionic

High melting point – solids at room T

Good conductors of electric current when molten

or dissolved in water

Bronsted-Lowry Definitions

An acid is any substance that can donate H+ ions

Acid = proton donator

A base is any substance that can accept H+ ions

Base = proton acceptor

H has only 1 electron and 1 proton, Thus, an H+ ion

is simply a proton!

Water

H3O+ is the hydronium ion, formed when water

accepts a protonHCl + H2O -> Cl - + H3O

+

OH- is the hydroxide ion, formed when water donates a proton

NH3 + H2O -> NH4+ + OH -

Amphoteric substances (such as water) donate protons in the presence of strong bases and accept protons in the presence of strong acids

Strong vs. Weak

Strong acids and bases completely dissociate in water –

break into ions

This makes them strong electrolytes

The acid dissociation constant, Ka, is a measure of acid

strength – stronger acids have larger Ka’s.

The base dissociation constant, Kb, is a measure of base

strength – strongerbases have larger Kb’s.

Weak acids and bases only partly dissociate in water.

They have dissociation constants < 1

pH Indicators

A substance that turns one color in an acid

solution and another color in a basic solution

pH paper; has a range of colors depending on pH

Litmus paper: turns Red in acid and Blue in Base

pH Scale

Numeric scale that shows the acidity or basicity

(alkalinity) of substances.

0 7 14Strong Acid Weak Acid Neutral Weak Base Strong Base

Buffers

Buffers: a mixture that is able to release or

absorb H+ ions, keeping the solution at a

constant pH.

Buffers neutralize acids and bases.

You can add a lot of acid or base to a buffered

solution with little or no change in pH

Titration

An Acid-Base Titration is a carefully controlled neutralization reaction. Titrations are used to determine the concentration of an unknown solution.

Standard Solution: an acid or base of known concentration

Equivalence Point: The point at which a reaction is neutralized.

End Point: The point at which an indicator changes color

See Sample problem p. 638

Titrations Continued

Strong Acid with a Strong Base

Very steep curve at equivalence point

A lot of Flexibility in choosing indicator

Weak Base with Strong Acid

Much smaller range for the steep part of the curve

Less flexibilthy in choosing indicator

Weak Acid with Strong Base

Also has smaller range for the steep part of the curve

Also have less flexibility in choosing indicator

pH = 7

pH < 7

pH > 7

Equivalence Point

Gas Properties

Have mass

Easy to compress

Fill their containers completely

Move through other gases quite rapidly

Exert pressure

Gas pressure depends on temperature

Kinetic Molecular TheoryExplains gas properties

1. Assumes gas consists of small particles that have mass

Particles are usually molecules but are atoms for the Noble gases

2. Gas particles are separated by relatively large distances

Thus they can be pushed together – compressed

3. Particle must be in constant rapid motion

4. Gases exert pressure because their particles frequently collide with other particles and container walls

5. The average kinetic energy of gas molecules depends only on temperature

6. Gas particles exert no force on one another

Boyles LawThe pressure and volume of a sample of gas at constant temperature are inversely proportional to each other

P1V1 = P2V2

Pressure Increases, Volume Decreases

Charles LawAt constant pressure, the volume of a fixed amount of gas is directly proportional to its absolute temperature

If T increases then V increases.

V1 = V2

T1 T2

The Ideal Gas Law

Describes the physical behavior of an ideal gas

A gas whose behavior is described by the

Kinetic Molecular Theory

Many real gases behave like ideal gases under

many ordinary conditions

Ideal Gas Law

PV = nRT, where

P = Pressure

V = Volume

n = number of moles

T = Temperature

R = the gas constant – calculated based on the fact that

1 mole of gas at STP occupies 22.4 L

R = 0.0821 atm-L/mol-K = 8.314 Pa-m3/Mol-K = 8.314 J/mol-K