Chapter 15

Acids and Bases

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TEKS• 10 (H) understand and differentiate among acid-

base reactions, precipitation reactions, and oxidation-reduction reactions;

• 10 (I) define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution; and

• 10 (J) distinguish between degrees of dissociation for strong and weak acids and bases.

Some Properties of Acids

Produce H+ (as H3O+) ions in water (the hydronium ion is a

hydrogen ion attached to a water molecule)

Taste sour

Corrode metals

Electrolytes

React with bases to form a salt and water

pH is less than 7

Turns blue litmus paper to red “Blue to Red A-CID”

Some Properties of Bases

Produce OHProduce OH-- ions in water ions in water

Taste bitter, chalkyTaste bitter, chalky

Are electrolytesAre electrolytes

Feel soapy, slipperyFeel soapy, slippery

React with acids to form salts and waterReact with acids to form salts and water

pH greater than 7pH greater than 7

Turns red litmus paper to blue “Turns red litmus paper to blue “BBasic asic BBlue”lue”

Anion Ending Acid Name

-ide hydro-(stem)-ic acid

-ate (stem)-ic acid

-ite (stem)-ous acid

Acid Nomenclature Review

No OxygenNo Oxygen

w/Oxygen w/Oxygen

An easy way to remember which goes with which…An easy way to remember which goes with which…

““In the cafeteria, youIn the cafeteria, you ATEATE somethingsomething ICICky”ky”

Arrhenius acid is a substance that produces H+ (H3O+) in water

Arrhenius base is a substance that produces OH- in water

4.3

Acid/Base definitionsDefinition 1: Arrhenius

Acid/Base Definitions

• Definition #2: Brønsted – LowryDefinition #2: Brønsted – Lowry

Acids – proton donorAcids – proton donor

Bases – proton acceptorBases – proton acceptor

A “proton” is really just a hydrogen A “proton” is really just a hydrogen atom that has lost it’s electron!atom that has lost it’s electron!

A Brønsted-Lowry acid is a proton donorA Brønsted-Lowry base is a proton acceptor

acidconjugate

basebase conjugate

acid

ACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIES

The Brønsted definition means NHThe Brønsted definition means NH33 is a is a BASE BASE in in

water — and water is itself anwater — and water is itself an ACIDACID

BaseAcidAcidBaseNH4

+ + OH-NH3 + H2OBaseAcidAcidBase

NH4+ + OH-NH3 + H2O

Conjugate PairsConjugate Pairs

Learning Check!

Label the acid, base, conjugate acid, and Label the acid, base, conjugate acid, and conjugate base in each reaction:conjugate base in each reaction:

HCl + OHHCl + OH--   Cl   Cl-- + H + H22OO HCl + OHHCl + OH--   Cl   Cl-- + H + H22OO

HH22O + HO + H22SOSO44   HSO   HSO44-- + H + H33OO

++ HH22O + HO + H22SOSO44   HSO   HSO44-- + H + H33OO

++

AcidAcidAcidAcid

AcidAcidAcidAcid

BaseBaseBaseBase

BaseBaseBaseBase

Conj.Conj.BaseBaseConj.Conj.BaseBase

Conj.Conj.BaseBaseConj.Conj.BaseBase

Conj.Conj.AcidAcidConj.Conj.AcidAcid

Conj.Conj.AcidAcidConj.Conj.AcidAcid

The The pH scalepH scale is a way of is a way of expressing the strength of expressing the strength of acids and bases. Instead of acids and bases. Instead of using very small numbers, using very small numbers, we just use the NEGATIVE we just use the NEGATIVE power of 10 on the Molarity power of 10 on the Molarity of the Hof the H++ (or OH (or OH--) ion.) ion.

Under 7 = acidUnder 7 = acid7 = neutral7 = neutral

Over 7 = base Over 7 = base

Calculating the pH

pH = - log [H+](Remember that the [ ] mean Molarity)

Example: If [H+] = 1 X 10-10

pH = - log 1 X 10-10

pH = - (- 10)

pH = 10

Example: If [H+] = 1.8 X 10-5

pH = - log 1.8 X 10-5

pH = - (- 4.74)

pH = 4.74

Try These!Try These!

Find the pH of these:Find the pH of these:

1)1) A 0.15 M solution of A 0.15 M solution of Hydrochloric acidHydrochloric acid

2) A 3.00 X 102) A 3.00 X 10-7-7 M M solution of Nitric solution of Nitric acidacid

pH = - log [HpH = - log [H++]]

pH = - log 0.15pH = - log 0.15

pH = - (- 0.82)pH = - (- 0.82)

pH = 0.82pH = 0.82

pH = - log 3 X 10pH = - log 3 X 10-7-7

pH = - (- 6.52)pH = - (- 6.52)

pH = 6.52pH = 6.52

pH calculations – Solving for H+pH calculations – Solving for H+pH calculations – Solving for H+pH calculations – Solving for H+

If the pH of Coke is 3.12, [HIf the pH of Coke is 3.12, [H++] = ???] = ???

Because pH = - log [HBecause pH = - log [H++] then] then

- pH = log [H- pH = log [H++]]

Take antilog (10Take antilog (10xx) of both) of both sides and get sides and get

1010-pH -pH == [H[H++]]

[H[H++] = 10] = 10-3.12-3.12 = 7.6 x 10 = 7.6 x 10-4-4 M M

*** to find antilog on your calculator, look for “Shift” *** to find antilog on your calculator, look for “Shift” or “2or “2nd nd function” and then the log buttonfunction” and then the log button

More About WaterMore About WaterHH22O can function as both an ACID and a BASE.O can function as both an ACID and a BASE.

In pure water there can beIn pure water there can be AUTOIONIZATIONAUTOIONIZATION

Equilibrium constant for water = KEquilibrium constant for water = Kww

KKww = [H = [H33OO++] [OH] [OH--] =] = 1.00 x 101.00 x 10-14-14 at 25 at 25 ooCC

More About WaterMore About Water

KKww = [H = [H33OO++] [OH] [OH--] = 1.00 x 10] = 1.00 x 10-14-14 at 25 at 25 ooCC

In a neutral solution [HIn a neutral solution [H33OO++] = [OH] = [OH--]]

and so [Hand so [H33OO++] = [OH] = [OH--] = 1.00 x 10] = 1.00 x 10-7-7 M M

OH-

H3O+

OH-

H3O+

AutoionizationAutoionization

pOH• Since acids and bases are Since acids and bases are

opposites, pH and pOH are opposites, pH and pOH are opposites!opposites!

• pOH does not really exist, but it is pOH does not really exist, but it is useful for changing bases to pH.useful for changing bases to pH.

• pOH looks at the perspective of a pOH looks at the perspective of a basebase

pOH = - log [OHpOH = - log [OH--]]Since pH and pOH are on opposite Since pH and pOH are on opposite

ends,ends,pH + pOH = 14pH + pOH = 14

pHpH [H+][H+] [OH-][OH-] pOHpOH

[H[H33OO++], [OH], [OH--] and pH] and pHWhat is the pH of the What is the pH of the

0.0010 M NaOH solution? 0.0010 M NaOH solution?

[OH-] = 0.0010 (or 1.0 X 10[OH-] = 0.0010 (or 1.0 X 10-3-3 M) M)

pOH = - log 0.0010pOH = - log 0.0010

pOH = 3pOH = 3

pH = 14 – 3 = 11pH = 14 – 3 = 11

OR KOR Kww = [H = [H33OO++] [OH] [OH--]]

[H[H3OO++] = 1.0 x 10] = 1.0 x 10-11-11 M M

pH = - log (1.0 x 10pH = - log (1.0 x 10-11-11) = 11.00) = 11.00

What is the pH of a 2 x 10-3 M HNO3 solution?

HNO3 is a strong acid – 100% dissociation.

HNO3 (aq) + H2O (l) H3O+ (aq) + NO3- (aq)

pH = -log [H+] = -log [H3O+] = -log(0.002) = 2.7

Start

End

0.002 M

0.002 M 0.002 M0.0 M

0.0 M 0.0 M

What is the pH of a 1.8 x 10-2 M Ba(OH)2 solution?

Ba(OH)2 is a strong base – 100% dissociation.

Ba(OH)2 (s) Ba2+ (aq) + 2OH- (aq)

Start

End

0.018 M

0.018 M 0.036 M0.0 M

0.0 M 0.0 M

pH = 14.00 – pOH = 14.00 + log(0.036) = 12.5615.4

HNO3, HCl, HBr, HI, H2SO4 and HClO4 are the strong acids.

Strong and Weak Acids/BasesStrong and Weak Acids/Bases

The strength of an acid (or base) is determined by the amount of IONIZATION.

The strength of an acid (or base) is determined by the amount of IONIZATION.

• Generally divide acids and bases into STRONG or Generally divide acids and bases into STRONG or WEAK ones.WEAK ones.

STRONG ACID:STRONG ACID: HNOHNO3 3 (aq) + H(aq) + H22O (l) O (l) HH33OO+ + (aq) + NO(aq) + NO33

- - (aq)(aq)

HNOHNO33 is about 100% dissociated in water. is about 100% dissociated in water.

Strong and Weak Acids/BasesStrong and Weak Acids/Bases

• Weak acidsWeak acids are much less than 100% ionized in are much less than 100% ionized in

water.water.

*One of the best known is acetic acid = CH*One of the best known is acetic acid = CH33COCO22HH

Strong and Weak Acids/BasesStrong and Weak Acids/Bases

• Strong Base:Strong Base: 100% dissociated in water.100% dissociated in water.

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

Other common strong Other common strong bases include KOH andbases include KOH and Ca(OH)Ca(OH)22..

CaO (lime) + HCaO (lime) + H22O -->O -->

Ca(OH)Ca(OH)22 (slaked lime) (slaked lime)

CaOCaO

Strong and Weak Acids/BasesStrong and Weak Acids/Bases

Strong bases are the group I hydroxidesStrong bases are the group I hydroxides

Calcium, strontium, and barium hydroxides are Calcium, strontium, and barium hydroxides are strong, but only soluble in water to 0.01 Mstrong, but only soluble in water to 0.01 M

• Weak base:Weak base: less than 100% ionized in waterless than 100% ionized in water

One of the best known weak bases is ammoniaOne of the best known weak bases is ammonia

NHNH3 3 (aq) + H(aq) + H22O (l) O (l) ↔↔ NH NH44+ + (aq) + OH(aq) + OH- - (aq)(aq)

Strong and Weak Acids/BasesStrong and Weak Acids/BasesStrong and Weak Acids/BasesStrong and Weak Acids/Bases

Weak BasesWeak Bases