Acids and Bases: Calculate Acids and Bases: Calculate pH/pOHpH/pOH

At the conclusion of our time At the conclusion of our time together, you should be able to:together, you should be able to:

1. Change any pH reading to pOH2. Convert pH to concentration of

hydronium ion concentrations, hydronium ion concentrations to pH

Since 1 mole of OHSince 1 mole of OH-- in one Liter of water in one Liter of water would be a pOH = 0would be a pOH = 0

And the pH and pOH of water is 7 or And the pH and pOH of water is 7 or neutral,neutral,

Therefore, the pH of a strong base with a Therefore, the pH of a strong base with a pOH of 0 would bepOH of 0 would be

pH = 14pH = 14 Therefore, any pH can be converted to Therefore, any pH can be converted to

pOH by subtracting from 14.pOH by subtracting from 14.

If an acid has a pH of 3, what would be If an acid has a pH of 3, what would be the pOH?the pOH?

14 – 3 = 14 – 3 = 1111 If an base has a pOH of 2, what would be If an base has a pOH of 2, what would be

the pH?the pH? 14 – 2 = 14 – 2 = 1212

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

(Remember that the [ ] mean Molarity)(Remember that the [ ] mean Molarity)

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

pH = - log 1 X 10pH = - log 1 X 10-10-10

pH = - (- 10)pH = - (- 10)

pH = 10pH = 10

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

pH = - log 1.8 X 10pH = - log 1.8 X 10-5-5

pH = - (- 4.74)pH = - (- 4.74)

pH = 4.74pH = 4.74

If the pH of Coke is 3.55, [HIf the pH of Coke is 3.55, [H++] = ???] = ???

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

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

Take antilog/inverse log (10Take antilog/inverse log (10xx) ) of of both sides and getboth sides and get

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

[H[H++] = ] = 1010-3.55-3.55 = 2.82 x 10 = 2.82 x 10-4-4 M M

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

If an acid has a pH of 3.55, what would be If an acid has a pH of 3.55, what would be the pOH?the pOH?

14 – 3.55 = 14 – 3.55 = 10.4510.45 What is the concentration of OHWhat is the concentration of OH--??

[OH[OH--] = 10] = 10-10.45-10.45 = = 3.55 x 103.55 x 10-11-11 M M

A solution has a [OHA solution has a [OH--] of 4.25 x 10] of 4.25 x 10-4-4. .

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

pOH = - log [4.25 x 10pOH = - log [4.25 x 10-4-4]]

pOH = 3.37pOH = 3.37

pH = 14 – 3.37 =pH = 14 – 3.37 =

10.6310.63

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

pOH = - log [4.25 x 10pOH = - log [4.25 x 10-4-4]]

pOH = 3.37pOH = 3.37

pH = 14 – 3.37 =pH = 14 – 3.37 =

10.6310.63

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

A Former Student Trying to Apply His A Former Student Trying to Apply His Knowledge of Chemistry!!Knowledge of Chemistry!!

[OH[OH--]]

[H[H++]] pOHpOH

pHpH

1010 -pOH

-pOH

1010 -pH-pH-Log[H

-Log[H++]]

-Log[OH

Log[OH

--]]

14 -

pOH

14 -

pOH

14 -

pH

14 -

pH

1.0

x 10

1.0

x 10-1

4-14

[OH[O

H-- ]]

1.0

x 10

1.0

x 10-1

4-14

[H[H

++ ]]

Acids and Bases: Calculate Acids and Bases: Calculate pH/pOHpH/pOH

Let’s see if you can:Let’s see if you can:

1. Change any pH reading to pOH2. Convert pH to concentration of

hydronium ion concentrations, hydronium ion concentrations to pH

The American Medical Association The American Medical Association announced today that the Universal announced today that the Universal

Choking Sign has been revised:Choking Sign has been revised:

Old Sign:Old Sign:

New Sign:New Sign:

Calvin’s Approach to Math in Chemistry:Calvin’s Approach to Math in Chemistry:

Get Your Clicker!!!

If a solution has a pH of 6.5, what is the If a solution has a pH of 6.5, what is the pOH of that same solution?pOH of that same solution?

4.5 7.5 6.5 012.5

20% 20% 20%20%20%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

1.1. 4.54.5

2.2. 7.57.5

3.3. 6.56.5

4.4. 0.00.0

5.5. 12.512.5

If a solution has a pH of 8.6, what is the If a solution has a pH of 8.6, what is the [H[H++] of that solution?] of that solution?

8.6

2.51 x 10-9

1.0 x 108.6

1.0 x 105.4 5.4

20% 20% 20%20%20%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

1.1. 8.68.6

2.2. 2.51 x 102.51 x 10-9-9

3.3. 1.0 x 101.0 x 108.68.6

4.4. 1.0 x 101.0 x 105.45.4

5.5. 5.45.4

If a solution has a pOH of 9.44, what is If a solution has a pOH of 9.44, what is the [OHthe [OH--] of that same solution?] of that same solution?

.975

1.00 x 109.44

3.63 x 10-10

4.569.44

20% 20% 20%20%20%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

1.1. 0.9750.975

2.2. 1.00 x 101.00 x 109.449.44

3.3. 3.63 x 103.63 x 10-10-10

4.4. 4.564.56

5.5. 9.449.44

If a solution has a [HIf a solution has a [H33OO++] of 6.20 x 10] of 6.20 x 10-8-8, ,

what is the pH of that solution?what is the pH of that solution?

6.798.79

5.214.56

7.21

20% 20% 20%20%20%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

1.1. 6.796.79

2.2. 8.798.79

3.3. 5.215.21

4.4. 4.564.56

5.5. 7.217.21

If a solution has a [OHIf a solution has a [OH--] of 1.05 x 10] of 1.05 x 10-3-3, , what is the pH of that solution?what is the pH of that solution?

11.022.98 1.

3.0210.98

20% 20% 20%20%20%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

1.1. 11.0211.02

2.2. 2.982.98

3.3. 1.001.00

4.4. 3.023.02

5.5. 10.9810.98

pH = 12.40, what would be the pOH?pH = 12.40, what would be the pOH? 14 – 12.40 = 14 – 12.40 = 1.601.60

What is the concentration of OHWhat is the concentration of OH--??

[OH[OH--] = 10] = 10-1.60-1.60 = = 0 0251 M0 0251 M

pOH? of 0.00162 M KOHpOH? of 0.00162 M KOH pOH = - log 0.00162pOH = - log 0.00162 = 2.79= 2.79 pH = 14 – 2.79 = pH = 14 – 2.79 = 11.2111.21

If an acid has a pH of 6, what would be If an acid has a pH of 6, what would be the pOH?the pOH?

14 – 6 = 14 – 6 = 88

What is the pH of the What is the pH of the 0.0010 M NaOH solution? 0.0010 M NaOH solution?

[OH[OH--] = 0.0010 (or 1.0 X 10] = 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

The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H+ ion concentration of the rainwater?

The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood?

1.51 x 10-5

pOH = 6.614.0 – 6.6 = 7.4 pH

Calculating [H3O+], pH, [OH-], and pOH

Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 3.0 M and (b) 0.0024 M. Calculate the [H3O+], pH, [OH-], and pOH of the two solutions at 25°C.

[H3O+] = 3.0 MpH = -0.47[OH-] = 3.388 x

10-15 MpOH = 14.47

[H3O+] = 0.0024 MpH = 2.6[OH-] = 3.98 x

10-12 MpOH = 11.4

Calculating [H3O+], pH, [OH-], and pOH

Problem 2: What is the [H3O+], [OH-], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral?

[H3O+] = 2.14 x 10-4 MpH = 3.67[OH-] = 4.677 x 10-11 MpOH = 10.33