Acids and Bases: Define and Acids and Bases: Define and Calculate pH/pOHCalculate pH/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. Define pH and pOH2. Explain the pH scale and what it means3. Change any pH reading to pOH4. Convert pH to concentration of

hydronium ion concentrations, hydronium ion concentrations to pH

Law of ProbabilityLaw of Probability

-The probability of  being watched is -The probability of  being watched is directly proportional to the stupidity of your directly proportional to the stupidity of your  act act

What is pH???What is pH???

p = countp = count H = Hydronium ionH = Hydronium ion (H(H33OO++)) In 1 Liter of water, (55+ moles of water), In 1 Liter of water, (55+ moles of water),

how many moles of hydronium ions are how many moles of hydronium ions are there???there???

Understanding pH gives me this Understanding pH gives me this number!!!number!!!

If there was 1 mole of HIf there was 1 mole of H33OO++ in 1 Liter of in 1 Liter of

water, (55+ moles of water), this count water, (55+ moles of water), this count would be 1 mole.would be 1 mole.

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

pH = -log[1]pH = -log[1] Therefore, by definition, the pH of this Therefore, by definition, the pH of this

solution is solution is = 0= 0

HH22O + HO + H22O O ---> ---> HH33OO++ + OH + OH--

<===<=== This equation indicates that most water This equation indicates that most water

molecules stay as molecules, very few will form molecules stay as molecules, very few will form hydronium ionshydronium ions

If we count the number of hydrogen ions in one If we count the number of hydrogen ions in one liter of water (pH) we would get:liter of water (pH) we would get:

.0000001 moles of H.0000001 moles of H33OO++/liter of water/liter of water

or 10or 10-7-7 moles of H moles of H33OO++/liter of water/liter of water

What is the pH of water??What is the pH of water?? pH = 7pH = 7

HH22O + HO + H22O O ---> ---> HH33OO++ + OH + OH--

<===<=== This equation indicates that most water This equation indicates that most water

molecules stay as molecules, very few will form molecules stay as molecules, very few will form hydroxide ionshydroxide ions

If we count the number of hydroxide ions in If we count the number of hydroxide ions in one liter of water (pOH) we would get:one liter of water (pOH) we would get:

.0000001 moles of OH.0000001 moles of OH--/liter of water/liter of water or 10or 10-7-7 moles of OH moles of OH--/liter of water/liter of water What is the pOH of water??What is the pOH of water?? pOH = 7pOH = 7

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

And the pH and pOH of water is 7 or neutral,And the pH and pOH of water is 7 or neutral, Therefore, the pH of a strong base with a Therefore, the pH of a strong base with a

pOH of 0 would be?pOH of 0 would be? pH = 14pH = 14 Therefore, the pH scale goes from 0-14Therefore, the pH scale goes from 0-14 Also, any pH can be converted to pOH by?Also, any pH can be converted to pOH by? Subtracting from 14.Subtracting from 14.

pH- The Amount Of H+ Ions In A Solution.

ACID extra H+1 ions (protons)

BASE fewer H+1 ions.

extra OH-1 ions.

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Where Do You Find a Dog With No Legs?Where Do You Find a Dog With No Legs?

Right Where You Left Him.Right Where You Left Him.

Let’s Try Some Calculations by Not UsingLet’s Try Some Calculations by Not UsingCalvin’s Approach to Math in Chemistry:Calvin’s Approach to Math in Chemistry:

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 = 10pH = 10

Example: If [HExample: If [H++] = 1.80 X 10] = 1.80 X 10-5-5

pH = - log 1.80 X 10pH = - log 1.80 X 10-5-5

pH = 4.7pH = 4.7

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 solution M solution of Nitric acidof Nitric acid

pH = 0.82

pH = 6.5

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

pH = 6.5

Remember, we are working with logarithms. Therefore, we will use the pHAD principle. Add significant figures after the Decimal Point for pH.

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++]]

Divide both sides by log orDivide both sides by log or

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

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

1010-3.12-3.12 = [H = [H++] = 7.6 x 10] = 7.6 x 10-4-4 M M

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

A solution has a pH of 3.78. What is the A solution has a pH of 3.78. What is the concentration of hydrogen ions in the concentration of hydrogen ions in the solution? (#1 on handout)solution? (#1 on handout)

pH = -log [H+] 3.78 = -log [H+]-3.78 = log [H+]Inverse log -3.78 = inverse log (log [H+])10-3.78 = [H+]1.66 x 10-4 = [H+]

If an acid has a pH of 3.78, what would be If an acid has a pH of 3.78, what would be the pOH? (#1 on handout)the pOH? (#1 on handout)

14 – 3.78 = 14 – 3.78 = 10.2210.22

A solution has a pH of 3.78. What is the A solution has a pH of 3.78. What is the concentration of hydroxide ions in the concentration of hydroxide ions in the solution? (#1 on handout)solution? (#1 on handout)

pOH = - log [OH-] 10.22 = - log [OH- ]- 10.22 = log [OH- ]Inverse log -10.22 = inverse log (log [OH- ])10-10.22 = [OH-]6.03 x 10-11 = [OH-]

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

Problem 1: What is the [H3O+], [OH-], and pOH of a solution with pH = 3.78? Is this an acid, base, or neutral?

[H3O+] = 1.66 x 10-4 MpOH = 10.22[OH-] = 6.03 x 10-11 MAcid

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

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

Example #4 on handout: Example #4 on handout:

If [OHIf [OH--] = 4.88 x 10] = 4.88 x 10-6-6

pOH = - log (4.88 x 10pOH = - log (4.88 x 10-6-6))

pOH = 5.31pOH = 5.31

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

Problem 2: A chemist dilutes concentrated hydrochloric acid to make:

0.000 389 M HCl. Calculate the pH, [OH-], and pOH

pH = 3.41pOH = 10.59[OH-] = 2.57 x 10-11 MAcid

[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

++ ]]

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

Acids and Bases: Define and Acids and Bases: Define and Calculate pH/pOHCalculate pH/pOHLet’s see if you can:Let’s see if you can:

1. Define pH and pOH2. Explain the pH scale and what it means3. Change any pH reading to pOH4. 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:

Get Your Clicker!!!

The “p” in pH stands for?The “p” in pH stands for?

1.1. PriorityPriority

2.2. CountCount

3.3. NumberNumber

4.4. MolarityMolarity

5.5. Not listedNot listed

The “H” in pH stands for?The “H” in pH stands for?

1.1. HouseHouse

2.2. Hydrogen ionsHydrogen ions

3.3. AcidAcid

4.4. ConcentrationConcentration

5.5. Not listedNot listed

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?

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

6.6. Not listedNot listed

If a solution has a pH of 6.2, what is the If a solution has a pH of 6.2, what is the [H[H++] of that solution?] of that solution?

1.1. 6.26.2

2.2. 6.3 x 106.3 x 10-7-7

3.3. 1.0 x 101.0 x 106.26.2

4.4. 1.0 x 101.0 x 107.87.8

5.5. 7.87.8

6.6. Not listedNot listed

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?

1.1. 0.980.98

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

6.6. Not listedNot listed

Let’s kick back and relax!!Let’s kick back and relax!!

Acids and Bases: Strength and Acids and Bases: Strength and IndicatorsIndicators

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. Determine the relative strength of acids and bases and the reason for the strengths

2. List the 3 basic types of indicators3. Explain each indicator’s strengths and

weaknesses4. Use an appropriate indicator to

determine the pH of a substance

HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.

Strong or Weak Acids/BasesStrong or 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 Generally divide acids and bases into STRONG or WEAK ones.STRONG or WEAK ones.

STRONG ACID: HNOSTRONG ACID: HNO3 3 (aq) + H(aq) + H22O (l) --->O (l) --->

HH33OO+ + (aq) + (aq) +

NONO33- - (aq)(aq)

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

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 = CHOne of the best known is acetic acid = CH33COCO22HH

Weak AcidsWeak AcidsWeak AcidsWeak Acids

Weak ACID

Strong ACID

HCl Hydrochloric acidH2SO4 Sulfuric acidHNO3 Nitric acid

CH3COOH Acetic acidH2CO3 Carbonic acid

Citric acid

pHpH HH22OO HH++

00 5555 11

11 550550 11

22 55005500 11

Strong BasesStrong Bases

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

Weak base: less than 100% ionized in waterWeak base: less than 100% ionized in water

One of the best known weak bases is One of the best known weak bases is ammoniaammonia

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

Weak BasesWeak BasesWeak BasesWeak Bases

Strong acids and bases dissolve in water

Hydrochloric, Hydrobromic, Hydroiodic, (All Binaries)

Nitric, Sulfuric, Perchloric Acids(Ternary Acids with 2 more O than H)

Group I hydroxides

Strong or Weak Acids/Bases Strong or Weak Acids/Bases SummarySummary

Maybe Our Goals Aren’t the Exact Same, But They’re Similar!!

There are three basic types:There are three basic types: PaperPaper pH meterpH meter Liquid indicatorsLiquid indicators (Some are natural liquid indicators like (Some are natural liquid indicators like

red cabbage, radishes)red cabbage, radishes)

Paper tests like litmus paper and pH Paper tests like litmus paper and pH paperpaper Put a stirring rod into the solution Put a stirring rod into the solution

and stir.and stir. Take the stirring rod out, and Take the stirring rod out, and

place a drop of the solution from place a drop of the solution from the end of the stirring rod onto a the end of the stirring rod onto a piece of the paperpiece of the paper

Read and record the color Read and record the color change. Note what the color change. Note what the color indicates.indicates.

Use a small portion of the paper. Use a small portion of the paper. You can use one piece of paper You can use one piece of paper for several tests.for several tests.

pH Paper

Blue Litmus paper

Red Litmus paper

Tests the voltage of the Tests the voltage of the electrolyteelectrolyte

Converts the voltage to pHConverts the voltage to pH Expensive, but very Expensive, but very

accurateaccurate Must be calibrated with a Must be calibrated with a

buffer solutionbuffer solution

Indicators are dyes that can Indicators are dyes that can be added that will change be added that will change color in the presence of an color in the presence of an acid or base.acid or base.

Some indicators only work Some indicators only work in a specific range of pHin a specific range of pH

Once the drops are added, Once the drops are added, the sample is ruinedthe sample is ruined

Some dyes are natural, like Some dyes are natural, like radish skin or red cabbageradish skin or red cabbage

We’ll Chip Away at this a Little at a Time!!

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

Acids and Bases: Strength and Acids and Bases: Strength and IndicatorsIndicators

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

1. Determine the relative strength of acids and bases and the reason for the strengths

2. List the 3 basic types of indicators3. Explain each indicator’s strengths and

weaknesses4. Use an appropriate indicator to

determine the pH of a substance

Get Your Clicker!!!

Red litmus paper will turn what color in Red litmus paper will turn what color in an acid?an acid?

1.1. BlueBlue

2.2. WhiteWhite

3.3. RedRed

4.4. ClearClear

5.5. Not listedNot listed

Which of the following would be the most Which of the following would be the most accurate way to test for pH?accurate way to test for pH?

1.1. pH meterpH meter

2.2. Litmus paperLitmus paper

3.3. Phenylthalein Phenylthalein

4.4. Cabbage juiceCabbage juice

5.5. Universal indicatorUniversal indicator

6.6. Not listedNot listed

Several liquids are tested for pH. Which Several liquids are tested for pH. Which of these liquids would be the weakest of these liquids would be the weakest

acid?acid?

1.1. Liquid a, pH = 1.0Liquid a, pH = 1.0

2.2. Liquid b, pH = 4.5Liquid b, pH = 4.5

3.3. Liquid c, pH = 6.5Liquid c, pH = 6.5

4.4. Liquid d, pH = 8.5Liquid d, pH = 8.5

5.5. Liquid e, pH = 10.5Liquid e, pH = 10.5

6.6. Liquid f, pH = 13.0Liquid f, pH = 13.0

So – What did you think of today’s So – What did you think of today’s class??class??

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?

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

6.6. Not listedNot listed

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?

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

6.6. Not listedNot listed

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 0.0001 M NaOH solution? 0.0001 M NaOH solution?

[OH[OH--] = 0.0001 (or 1.0 X 10] = 0.0001 (or 1.0 X 10-4-4 M) M)

pOH = - log 0.0001pOH = - log 0.0001

pOH = 4pOH = 4

pH = 14 – 4 = 10pH = 14 – 4 = 10

The pOH of rainwater collected in a certain region of the northeastern United States on a particular day was 9.94. What is the H+ ion concentration of the rainwater?

The OH- ion concentration of a blood sample is 2.88 x 10-6 M. What is the pH of the blood?

pH = 4.068.91 x 10-5

pOH = 5.5414.0 – 5.54 = 8.46 pH

I wouldn’t do that if I were

you!!!