Acids & Bases

The ammeter measures the flow of electrons (current) through the circuit.

If the ammeter measures a current, and the bulb glows, then the solution conducts.

If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting.

Electrolytes vs. NonelectrolytesElectrolytes vs. Nonelectrolytes

An electrolyte is:

A substance whose aqueous solution conducts an electric current.

A nonelectrolyte is:

A substance whose aqueous solution does not conduct an electric current.

Try to classify the following substances as electrolytes or nonelectrolytes…

Definition of Electrolytes and Definition of Electrolytes and NonelectrolytesNonelectrolytes

1.Pure water2.Tap water3.Sugar solution4.Sodium chloride solution5.Hydrochloric acid solution6.Lactic acid solution7.Ethyl alcohol solution8.Pure sodium chloride

Electrolytes?Electrolytes?

ELECTROLYTES: NONELECTROLYTES:

Tap water (weak)

NaCl solution

HCl solution

Lactate solution (weak)

Pure water

Sugar solution

Ethanol solution

Pure NaCl

But why do some compounds conduct electricity insolution while others do not…?

Answers to ElectrolytesAnswers to Electrolytes

Electrolytes

• Ionization– Formation of ions caused by a reaction

between water molecules

• Strong– Large amount of ionization occurs

• Weak– Small amount of ionization occurs

Arrhenuis Definition

• A substance that produces hydrogen ions (hydronium ions) as the only + ion when mixed with water

• H+ = Hydrogen ion

• H3O+ = Hydronium ion

• The greater the # of H3O+ ions the stronger the acid and the stronger the electrolyte

Strong Acids vs. Weak AcidsStrong Acids vs. Weak Acids

Strong acids are assumed to be 100% ionized in solution (good proton donors).

Weak acids are usually less than 5% ionized in solution (poor proton donors).

HCl

H2SO4 HNO3

H3PO4 HC2H3O2 Organic acids

Strong Acid IonizationStrong Acid Ionization

Weak Acid IonizationWeak Acid Ionization

Organic AcidsOrganic AcidsOrganic acids all contain the “carboxyl” group, sometimes several of them.

The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.

Examples of Organic AcidsExamples of Organic Acids

Citric acid in citrus fruitCitric acid in citrus fruit Malic acid in sour applesMalic acid in sour apples Deoxyribonucleic acid, DNADeoxyribonucleic acid, DNA Amino acids, the building blocks of Amino acids, the building blocks of

proteinprotein Lactic acid in sour milk and sore musclesLactic acid in sour milk and sore muscles Butyric acid in rancid butterButyric acid in rancid butter

Properties of AcidsProperties of Acids Acids taste sour

Acids effect indicators Blue litmus turns red Methyl orange turns red

Acids have a pH lower than 7

Acids are proton (hydrogen ion, H+) donors

Acids react with active metals, produce H2

Acids neutralize bases

Acids you SHOULD know:Acids you SHOULD know:

Strong Acids Weak Acids

Hydrochloric acid, HCl

Nitric acid, HNO3

Sulfuric acid, H2SO4 Phosphoric acid, H3PO4

Acetic acid, HC2H3O2

Sulfuric AcidSulfuric Acid Highest volume production of any chemical in Highest volume production of any chemical in

the U.S.the U.S. Used in the production of paperUsed in the production of paper Used in production of fertilizersUsed in production of fertilizers Used in petroleum refiningUsed in petroleum refining

Thick clouds of sulfuric acid are a feature of the atmosphere of Venus.

(image provided by NASA)

Nitric AcidNitric Acid• Used in the production of Used in the production of

fertilizersfertilizers

• Used in the production of Used in the production of explosivesexplosives

• Nitric acid is a volatile acid Nitric acid is a volatile acid

– its reactive components– its reactive components evaporate easilyevaporate easily

• Stains proteins (including Stains proteins (including skin!)skin!)

Nitric AcidNitric Acid

• Used in the production of fertilizersUsed in the production of fertilizers• Used in the production of Used in the production of

explosivesexplosives• Nitric acid is a volatile acid – its Nitric acid is a volatile acid – its

reactive componentsreactive components evaporate evaporate easilyeasily

• Stains proteins (including skin!)Stains proteins (including skin!)

Hydrochloric AcidHydrochloric Acid• Used in the pickling of Used in the pickling of

steelsteel

• Used to purify Used to purify magnesium from sea magnesium from sea waterwater

• Part of gastric juice, it Part of gastric juice, it aids in the digestion of aids in the digestion of proteinprotein

• Sold commercially as Sold commercially as “Muriatic acid”“Muriatic acid”

Phosphoric Phosphoric AcidAcid

o A flavoring agent in A flavoring agent in sodassodas

o Used in the manufacture Used in the manufacture of detergentsof detergents

o Used in the manufacture Used in the manufacture of fertilizersof fertilizers

o NotNot a common a common laboratory reagentlaboratory reagent

Acetic AcidAcetic AcidUsed in the manufacture of Used in the manufacture of

plasticsplasticsUsed in making Used in making

pharmaceuticalspharmaceuticalsAcetic acid is the acid Acetic acid is the acid

present in vinegarpresent in vinegar

Acids are Proton DonorsAcids are Proton Donors

Monoprotic acidsDiprotic acids Triprotic acids

HCl

HC2H3O2

HNO3

H2SO4

H2CO3

H3PO4

Acids Effect IndicatorsAcids Effect Indicators

Blue litmus paper turns red in contact with an acid.

Acids Acids Have a Have a pH less pH less than 7than 7

Acids React with Active Acids React with Active MetalsMetals

Acids react with active metals to form salts and hydrogen gas.

Mg + 2HCl MgCl2 + H2(g)

Zn + 2HCl ZnCl2 + H2(g)

Mg + H2SO4 MgSO4 + H2(g)

Effects of Acid Rain on MarbleEffects of Acid Rain on Marble(calcium (calcium carbonatecarbonate))

George Washington:BEFORE

George Washington:AFTER

Arrhenuis Base

• A base is any Hydroxide that dissolves in water to yield hydroxide ions as the only negative ion

• NaOH

• KOH

• Mg(OH)2

Properties of BasesProperties of Bases Bases taste bitter

Bases effect indicators Red litmus turns blue Phenolphthalein turns hot pink

Bases have a pH greater than 7

Bases are proton (hydrogen ion, H+) acceptors

Solutions of bases feel slippery

Bases neutralize acids

Examples of BasesExamples of Bases

Sodium hydroxide (lye), NaOHSodium hydroxide (lye), NaOH Potassium hydroxide, KOHPotassium hydroxide, KOH Magnesium hydroxide, Mg(OH)Magnesium hydroxide, Mg(OH)22

Calcium hydroxide (lime), Ca(OH)Calcium hydroxide (lime), Ca(OH)22

Bases Effect IndicatorsBases Effect Indicators

Red litmus paper turns blue in contact with a base. Phenolphthale

in turns purple in a base.

Bases Bases have a pH have a pH

greater greater than 7than 7

Bases Neutralize Bases Neutralize AcidsAcids

Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl.

2 HCl + Mg(OH)2

MgCl2 + 2 H2O

Acids Neutralize BasesAcids Neutralize Bases

HCl + NaOH NaCl + H2O

Neutralization reactions ALWAYS produce a salt and water.

H2SO4 + 2NaOH Na2SO4 + 2H2O

2HNO3 + Mg(OH)2 Mg(NO3)2 + 2H2O

Acid-Base Acid-Base Titration Titration and pHand pH

Self-Ionization of WaterSelf-Ionization of Water

H2O + H2O H3O+ + OH-

Though pure water is considered a non-conductor, there is a slight, but measurable conductivity due to “self-ionization”

Ion Concentration in SolutionsIon Concentration in Solutions

pH pH ScalScal

ee

Interpreting pH

• The term “pH” means power of hydrogen

• Refers to the H+ ions released by the acids to form H3O+ ions

• The more H+ released the more H3O+ and the lower the pH and stronger the acid

• The lower the pH the greater the power of Hydrogen

pH

• The negative logarithm , to the base 10, of the H+ concentration

• The log to the base 10 of a power 10 is equal to the power

• -log [10-7] = 7

H+, OH-, and pHH+, OH-, and pH

Calculating pH, pOHCalculating pH, pOH

pH = -log10(H3O+)

pOH = -log10(OH-)

Relationship between pH and Relationship between pH and pOHpOH

pH + pOH = 14

Finding [HFinding [H33OO++], [OH], [OH--] from pH, pOH] from pH, pOH

[H3O+] = 10-pH

[OH-] = 10-pOH

KKww – Ionization Constant for – Ionization Constant for

WaterWaterIn pure water at 25 C:

[H3O+] = 1 x 10-7 mol/L

[OH-] = 1 x 10-7 mol/L

Kw is a constant at 25 C:

Kw = [H3O+][OH-]

Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-

14

Titrations

• The molarity of an acid (or base) of unknown concentration can be determined by slowly combining it with a base(or acid) of known molarity(standard solution) until neutralization occurs

• A method of determining the concentration of an acid or base by neutralizing it with a solution of known concentration

• The end point is determined by the use of indicators. ( endpoint – when the right amount of standard solution has been added and neutralization as occurred)

Titration

• Moles = Volume x Molarity

• naVaMa = nbVbMb

• na = # of H+ ions Ma = Molarity of acid

• nb = # of OH- ions Mb = Molarity of base

• Va = Volume of acid

• Vb = Volume of base

pH CalculationspH Calculations

H + O H -

pH pO H

[O H -] = 1 x 10 - 1 4

[H + ]

[H + ] = 1 x 10 - 1 4

[O H -]

p O H = 14 - p H

p H = 14 - p O H

pOH

= -l

og[O

H- ]

pH =

-log

[H+

]

[OH

- ] = 1

0-pO

H

[H+

] = 1

0-pH

Measuring pH with wide-range Measuring pH with wide-range paperpaper

Narrow-Range pH PaperNarrow-Range pH Paper

Indicators

• An indicator is a weak acid (or base) that changes its color in a known pH range when it gains or loses a H+ ion.

• Phenolphthalein is a common indicator that is colorless when it is protonated (contains a H+) when it reacts with a base it loses it H+ and turns pink

Measuring pH

• Phenolphthalein changes from colorless to pink at pH 7–9.

Measuring pH19.2

pH pH IndicatorIndicator

s s and theirand theirrangesranges

Measuring pHAcid-Base Indicators

• Universal Indicators

19.2

1

2

3

4

5

6

7

8

9

10

11

12

13

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00m illiliters NaOH (0.10 M)

pH

Weak Acid/Strong Base TitrationWeak Acid/Strong Base Titration

A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH

Endpoint is above pH 7

1

2

3

4

5

6

7

8

9

10

11

12

13

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00

m illiliters NaOH (0.10 M)

pH

Strong Acid/Strong Base TitrationStrong Acid/Strong Base Titration

A solution that is 0.10 M HCl is titrated with 0.10 M NaOH

Endpoint is at pH 7

1

2

3

4

5

6

7

8

9

10

11

12

13

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00

m illiliters HCl (0.10 M)

pH

Strong Acid/Strong Base TitrationStrong Acid/Strong Base Titration

A solution that is 0.10 M NaOH is titrated with 0.10 M HCl

Endpoint is at pH 7 It is important to

recognize that titration curves are not always increasing from left to right.

1

2

3

4

5

6

7

8

9

10

11

12

13

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00

m illiliters NH3 (0.10 M)

pH

Strong Acid/Weak Base TitrationStrong Acid/Weak Base Titration

A solution that is 0.10 M HCl is titrated with 0.10 M NH3

Endpoint is below pH 7