Acid-Base Equilibrium Learning Goal: I will understand the Bronsted-Lowry Theory of acids and bases, be able to identify conjugate acid/base pairs, understand.

Acid-Base Equilibrium

Learning Goal: Learning Goal:

I will understand the Bronsted-Lowry Theory of acids and bases, I will understand the Bronsted-Lowry Theory of acids and bases, be able to identify conjugate acid/base pairs, understand what the be able to identify conjugate acid/base pairs, understand what the

autoionization of water means, and understand the difference autoionization of water means, and understand the difference between strong and weak acids/bases.between strong and weak acids/bases.

I will be able to perform calculations to solve for the equilibrium I will be able to perform calculations to solve for the equilibrium constant (Kw) of the autoionization of water.constant (Kw) of the autoionization of water.

I will understand what the pH scale really means, and use this I will understand what the pH scale really means, and use this knowledge to convert between pH, pOH and the concentration of knowledge to convert between pH, pOH and the concentration of

[H+] and [OH-] ions in solution.[H+] and [OH-] ions in solution.

Acids and BasesArrheniusArrhenius

acids:acids: generate Hgenerate H++ in water in water

bases:bases: generate OHgenerate OH-- in water in water

BrBrønsted-Lowryønsted-Lowry

acids:acids: HH++ donors donors

bases:bases: HH++ acceptors acceptors

HCl + HHCl + H22O O Cl Cl + H + H33OO++

acidacid base base

H3O+ = H+(aq) = proton in water

Conjugate acid-base pairsConjugate base:Conjugate base:

remains after Hremains after H++ is lost is lost

acid: HClacid: HCl conj. base:conj. base: ClCl--

Conjugate acid:Conjugate acid:

remains after Hremains after H++ is gained is gained

base: NHbase: NH33 conj. acid:conj. acid: NHNH44++

A- HB+HA B-+

Conjugate Pair

Conjugate Pair

A- HB+HA B-+

Conjugate Pair

Conjugate Pair

Label the Conjugate Acid Base Pairs for Each of the Following:

Strong and Weak Acids

Strong:Strong: 100% dissociation100% dissociation

good Hgood H++ donor donor

equilibrium lies far to right (HNOequilibrium lies far to right (HNO33))

generates weak base (NOgenerates weak base (NO33--))

Weak:Weak: <100% dissociation<100% dissociation

not-as-good Hnot-as-good H++ donor donor

equilibrium lies far to left (CHequilibrium lies far to left (CH33COOH)COOH)

generates strong base (CHgenerates strong base (CH33COOCOO--))

Strong Acids and Bases

Very strong

Strong

Weak

Very weak

Relative Acid Strength

Relative Conj. Base Strength

Very weak

Weak

Strong

Very strong

The stronger the acid, the weaker its conjugate base, and conversely, the weaker

the acid, the stronger its conjugate base

AcidAcid Base Base Conj. Acid Conj. Base Conj. Acid Conj. Base

Water is amphoteric/amphiprotic) meaning it can act as an acid (donates a proton)or a base (accepts a proton)

Even pure water conducts electricity, which means it exists as an equilibrium between H2O (l), H3O+ (aq) and OH-(aq)

OHaq)(OH (l) OH 32

Scientists often omit the water molecule that carries the H+ ion, so the autoionization of water can be changed from:

Water equilibrium obeys equilibrium law, and can be written as (H2O is excluded because it’s in liquid state):

OHaq)(OH (l) OH 32

to:

OHaq)(H (l) OH 2

STPat14-3w 101]][OHO[H K

Equilibrium Equation for

Autoionization of Water:

Therefore:

neutral solutions: [H [H++(aq)(aq)] = [OH] = [OH--

(aq)(aq)]] =1.0 x10-7 mol/L

(pure water)

acidic solutions: [H[H++(aq)(aq)] > [OH] > [OH--

(aq)(aq)]] >1.0 x10-7 mol/L

basic solutions: [H[H++(aq)(aq)] < [OH] < [OH--

(aq)(aq)]] <1.0 x10-7 mol/L

[H+(aq)] vs [OH-

(aq)]

STPat14w 101K

Since:

Strength of Acids/Bases

Strong:Strong:

100% dissociation100% dissociation

Ex: Strong Base:Ex: Strong Base:

NaOHNaOH(s)(s) Na Na++(aq)(aq) + OH + OH--

(aq)(aq)

Weak:Weak:

<100% dissociation<100% dissociation

Ex: Weak BaseEx: Weak BaseCHCH33NHNH2(aq)2(aq) + H + H22OO(l) (l) CHCH33NHNH2(aq)2(aq) + OH + OH--

(aq)(aq)

Example #1: Calculating Unknown Concentrations of [H+

(aq)] or [OH-(aq)]

Calculate the hydrogen ion concentration in a 0.25mol/L aqueous Calculate the hydrogen ion concentration in a 0.25mol/L aqueous barium hydroxide (a strong base) solution.barium hydroxide (a strong base) solution.

You Try #1: Calculating Unknown Concentrations of [H+

(aq)] or [OH-(aq)]

A 0.15M solution of hydrochloric acid (a strong acid) at SATP has a A 0.15M solution of hydrochloric acid (a strong acid) at SATP has a hydrogen ion concentration of 0.15M. Calculate the concentration of hydrogen ion concentration of 0.15M. Calculate the concentration of hydroxide ions. Assume STP conditions.hydroxide ions. Assume STP conditions.

Let’s Try Together: Calculating Unknown Concentrations of [H+

(aq)] or [OH-(aq)]

Determine the hydrogen ion and hydroxide ion concentration in Determine the hydrogen ion and hydroxide ion concentration in 500mL of an aqueous solution containing 2.6g of dissolved NaOH.500mL of an aqueous solution containing 2.6g of dissolved NaOH.

What Does pH Really Mean?A measure of the hydronium/hydrogen ion

The hydrogen concentration can range anywhere from 10mol/L The hydrogen concentration can range anywhere from 10mol/L to 1x10to 1x10-15-15mol/L. The pH scale must be able to cover a large mol/L. The pH scale must be able to cover a large range, so a logarithmic scale that covers factors of 10 is used. range, so a logarithmic scale that covers factors of 10 is used.

The “p” in pH stands for log.The “p” in pH stands for log.

A solution with a pH of 1 has [HA solution with a pH of 1 has [H33OO++] or [H] or [H++] of 0.1 mol/L or 10] of 0.1 mol/L or 10-1-1

— a pH of 3 has [Ha pH of 3 has [H33OO++]/ [H]/ [H++] of 0.001 mol/L or 10] of 0.001 mol/L or 10-3-3

— a pH of 7 has [Ha pH of 7 has [H33OO++]/ [H]/ [H++] of 0.0000001 mol/L or 10] of 0.0000001 mol/L or 10-7-7

pH = - log [H3O+]

Or

pH = - log [H+]

The pH scale

The pH scale ranges from 1 to 1x 10The pH scale ranges from 1 to 1x 10-14-14 mol/L or from 1 mol/L or from 1

to 14.to 14.

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

1 2 3 4 5 61 2 3 4 5 6 77 8 9 10 11 12 13 148 9 10 11 12 13 14

acidacid neutral neutral basebase

Manipulating pH

Algebraic manipulation of:

pH = - log [HpH = - log [H33OO++]]

allows for:

[H[H33OO++] = 10] = 10-pH-pH

If pH is a measure of the hydronium ion concentration then the same equations could be used to describe the hydroxide (base) concentration.

[OH[OH--] = 10] = 10-pOH-pOH pOH = - log [OHpOH = - log [OH--]] thus:

pH + pOH = 14 pH + pOH = 14 ; the entire pH range!; the entire pH range!

pH and pOH Formula Summary

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

[H[H++] = 10] = 10-pH-pH

pOH = - log [OHpOH = - log [OH--]]

[OH[OH--] = 10] = 10-pOH-pOH

pH + pOH = 14 pH + pOH = 14 (at SATP)(at SATP)

Example #1Calculate the pH of a solution with a hydrogen ion Calculate the pH of a solution with a hydrogen ion

concentration of 4.7 x10concentration of 4.7 x10-11 -11 mol/Lmol/L

You Try #1Calculate the pOH of a solution with a hydroxide ion Calculate the pOH of a solution with a hydroxide ion

concentration of 3.0x10concentration of 3.0x10-6 -6 mol/Lmol/L

Example # 2What is the hydrogen ion concentration of a solution with a pH What is the hydrogen ion concentration of a solution with a pH

of 10.33?of 10.33?

You Try # 2What is the hydroxide ion concentration of a solution with a What is the hydroxide ion concentration of a solution with a

pOH 6.2?pOH 6.2?

Let’s Try TogetherWhat is the pOH of a solution whose pH is 8.4?What is the pOH of a solution whose pH is 8.4?

Let’s Throw Another Equation into the Mix

Recap:

In neutral solutions: [H+(aq)] = [OH-

(aq)] =1.0 x10-7 mol/L

That means, at Kw= 1.0 x10-7 mol/L

Therefore, pKw=-logKw

And pH + pOH =pKw =14 (at STP)

Example #3Calculate the pH, pOH and [OH-] Calculate the pH, pOH and [OH-]

of a 0.042 mol/L HNOof a 0.042 mol/L HNO33 (aq) solution. (aq) solution.

You Try #3Calculate the pH, pOH and [OH-] Calculate the pH, pOH and [OH-]

of a 0.0020M HBr (aq) solution.of a 0.0020M HBr (aq) solution.

Acid-Base Equilibrium

Learning Goal: Learning Goal:

I will understand the Bronsted-Lowry Theory of acids and bases, I will understand the Bronsted-Lowry Theory of acids and bases, be able to identify conjugate acid/base pairs, understand what the be able to identify conjugate acid/base pairs, understand what the

autoionization of water means, and understand the difference autoionization of water means, and understand the difference between strong and weak acids/bases.between strong and weak acids/bases.

I will be able to perform calculations to solve for the equilibrium I will be able to perform calculations to solve for the equilibrium constant (Kw) of the autoionization of water.constant (Kw) of the autoionization of water.

I will understand what the pH scale really means, and use this I will understand what the pH scale really means, and use this knowledge to convert between pH, pOH and the concentration of knowledge to convert between pH, pOH and the concentration of

[H+] and [OH-] ions in solution.[H+] and [OH-] ions in solution.