ObjectivesObjectivesProperties of acids and basesProperties of acids and basesThe pH scaleThe pH scaleDistinguish between strong and weak Distinguish between strong and weak acids and list the uses of these acidsacids and list the uses of these acidsDistinguish between strong and weak Distinguish between strong and weak bases and list the uses of these basesbases and list the uses of these basesUnderstand neutralization and Understand neutralization and applications of neutralizationapplications of neutralization

An An acidacid (from the Latin (from the Latin acidusacidus meaning meaning soursour) is traditionally considered any ) is traditionally considered any chemical chemical compound that, when compound that, when dissolved in water, gives a solution dissolved in water, gives a solution with a hydrogen ion activity greater with a hydrogen ion activity greater than in pure waterthan in pure water, i.e. a , i.e. a pH less than pH less than 7.0. 7.0.

In chemistry, a In chemistry, a basebase is most commonly is most commonly thought of as an thought of as an aqueous substance that aqueous substance that can accept hydrogen ionscan accept hydrogen ions. Bases . Bases are are also the oxides or hydroxides of also the oxides or hydroxides of metals. metals.

Acids and Bases

Solutions can be sorted by whether they are: acid, basic (alkali) or neutral.

When a substance dissolves in water it makes a solution.

Acids & BasesAcids

Taste sour Turns litmus red Neutralizes bases Acids are made of one

or more H+ ions and one negative ion

Ex. HCl Produces H+ ions when

dissolved in water Are corrosive

Bases Taste bitter Turns litmus blue Neutralizes acids Bases are made of

metals combined with hydroxide ions (OH-)

Ex. NaOH Produces OH- when

dissolved in water Feel slippery or

“soapy”

Are corrosive

General propertiesGeneral properties

ACIDSACIDS

Taste sourTaste sour

Turn litmusTurn litmus

React with active metals – React with active metals – Fe, ZnFe, Zn

React with basesReact with bases

BASESBASES

Taste bitterTaste bitter

Turn litmusTurn litmus

Feel soapy or slippery Feel soapy or slippery (react with fats to (react with fats to make soap)make soap)

React with acidsReact with acids

blue to red red to blue

DefinitionsDefinitions

Acids – produce HAcids – produce H++

Bases - produce OHBases - produce OH--

Acids – donate HAcids – donate H++

Bases – accept HBases – accept H++

Arrehenius

Bronsted-Lowry

only in water

any solvent

NeutralizationNeutralization

In general: Acid + Base Salt + Water

All neutralization reactions are double displacement reactions.

HCl + NaOH NaCl + HOH

HCl + Mg(OH)2

H2SO4 + NaHCO3

Acids & Bases

STRONG vs WEAKSTRONG vs WEAK_ _ completely ionizedcompletely ionized _ partially ionized_ partially ionized_ strong electrolyte_ strong electrolyte _ weak electrolyte_ weak electrolyte

Strong AcidsStrong Acids:: Strong Bases:Strong Bases:HClOHClO44 LiOHLiOHHH22SOSO44 NaOHNaOHHIHI KOHKOHHBrHBr Ca(OH)Ca(OH)22

HClHCl Sr(OH)Sr(OH)22

HNOHNO33 Ba(OH)Ba(OH)22

Examples

Strong AcidsStrong Acids:: Strong Bases:Strong Bases:

HClOHClO44 LiOHLiOH

HH22SOSO44 NaOHNaOH

HIHI KOHKOH

HBrHBr Ca(OH)Ca(OH)22

HClHCl Sr(OH)Sr(OH)22

HNOHNO33 Ba(OH)Ba(OH)22

HA

Let’s examine the behavior of an acid, HA, in aqueous solution.

What happens to the HA molecules in solution?

HA

H+

A-

Strong Acid

100% dissociation of HA

Would the solution be conductive?

HA

H+

A-

Weak Acid

Partial dissociation of HA

Would the solution be conductive?

Marieb, Fig 26.11

Strong and Weak Acids/BasesStrong and Weak Acids/BasesStrong acids/bases – 100% dissociation into ions

HCl NaOHHNO3 KOHH2SO4

Weak acids/bases – partial dissociation, both ions and molecules

CH3COOH NH3

pH

2 3 4 5 6 7 8 9 10 11 12

neutral @ 25oC(H+) = (OH-)

distilled water

acidic(H+) > (OH-)

basic or alkaline(H+) < (OH-)

natural waters pH = 6.5 - 8.5

normal rain (CO2)pH = 5.3 – 5.7

acid rain (NOx, SOx)pH of 4.2 - 4.4 in Washington DC area

0-14 scale for the chemists

fish populationsdrop off pH < 6 and to zero pH < 5

On the pH scale, values below 7 are acidic, a value of 7 is neutral, and values above 7 are basic.

Marieb, 2.12

You are

here!

http://nadp.sws.uiuc.edu/isopleths

pH of Rainwateracross United States in 2001

Incre

asin

g a

cidity

Why is the eastern US more acidic?

air masses

What is acid rain?What is acid rain?

CO2 (g) + H2O H2CO3 H+ + HCO3-

Dissolved carbon dioxide lowers the pH

Atmospheric pollutants from combustion

NO, NO2 + H2O … HNO3

SO2, SO3 + H2O … H2SO4

bothstrong acids

pH < 5.3

VocabularyVocabularyHydronium ionHydronium ion -is the common name for -is the common name for the aqueous cation Hthe aqueous cation H33OO+ +

Hydroxide ionHydroxide ion – common name for the – common name for the aqueous anion OHaqueous anion OH--

IndicatorIndicator –is a chemical compound that is –is a chemical compound that is added in small amounts to a solution so added in small amounts to a solution so that the pH (acidity or basicity) of the that the pH (acidity or basicity) of the solution can be determined visually. solution can be determined visually.

BuffersBuffers - make the pH of the solution - make the pH of the solution change very little when a small amount of change very little when a small amount of strong acid or base is added to it. strong acid or base is added to it.

VocabularyVocabularySoapsSoaps -a cleansing agent created by the -a cleansing agent created by the chemical reaction of a fatty acid with an alkali chemical reaction of a fatty acid with an alkali metalmetal hydroxide. (KOH) hydroxide. (KOH)

DetergentsDetergents -developed in response to the -developed in response to the shortage of the animal and vegetable fats used shortage of the animal and vegetable fats used to make soap during World War I and World War to make soap during World War I and World War II. Detergents are primarily surfactants, which II. Detergents are primarily surfactants, which could be produced easily from petrochemicals.could be produced easily from petrochemicals.

TitrationTitration -one solution (solution #1) is added to -one solution (solution #1) is added to another solution (solution #2) until a chemical another solution (solution #2) until a chemical reaction between the components in the reaction between the components in the solutions has run to completion. solutions has run to completion.

1.1. What does pH stand for?What does pH stand for?2.2. Define acid.Define acid.3.3. Define base.Define base.4.4. List the properties of acidsList the properties of acids5.5. List the properties of basesList the properties of bases6.6. Define indicatorDefine indicator7.7. Define soap (how are they made)Define soap (how are they made)8.8. What do we mean by neutralizationWhat do we mean by neutralization

pH CalculationspH Calculations

pH

pOH

[H+]

[OH-]

pH + pOH = 14

pH = -log[H+]

[H+] = 10-pH

pOH = -log[OH-]

[OH-] = 10-pOH

[H+] [OH-] = 1.0 x10-14

pH and pOH calculationspH and pOH calculations

1.1. What is the pOH of a solution whose pH is 3.45?

2. What is the [OH-] of a solution whose pOH = 2.86 ?

3. The pH of a softdrink is determined to be 4.0. What is the [OH-] of the drink?

4. What is the pOH of a solution whose [H+] is 2.75 x 10-4 M?

5. What is the [H+] of a solution whose pOH = 2.86 ?

6. What is the pH of a solution whose pOH is 11.09?

7. What is the [H+] of an acid solution that has a pH of 3?