Acids, Bases and pHChapter 19

Compounds That Become Acids When Dissolved in Water

General Formula: HX

H+ X-

monatomic

or

polyatomic

anion

Naming Acids (p. 250)

Binary acids

Hydro_______ic Acid

HCl: Hydrochloric acid

HBr: Hydrobromic acid

HS: Hydrosulfuric acid

Oxyacids

ite becomes ous

Acid from chlorite:

HClO2 = chlorous acid

Acid from phosphite:

H3PO3 = phosphorous acid

ate becomes ic

Acid from sulfate:

H2SO4 = sulfuric acid

Compounds That Become Acids When Dissolved in Water

Your turn:

HBr

HNO2

HNO3

Compounds That Become Acids When Dissolved in Water

Your turn:

HBr

hydrobromic acid

HNO2nitrous acid

HNO3nitric acid

Practice

Name or write formulas for the following acids:

1. Phosphoric Acid 5. HClO42. Hydrochloric Acid 6. HI

3. Chlorous Acid 7. H2S

4. Sulfurous Acid 8. HC2H3O29. Write the balanced formula, total ionic and net

ionic equations for the acid base neutralization reaction that occurs when aqueous sulfuric acid is mixed with aqueous potassium hydroxide

Practice

Name or write formulas for the following acids:

1. phosphoric acid H3PO42. hydrochloric acid HCl

3. chlorous Acid HClO24. sulfurous Acid H2SO35. HClO4 perchloric acid

6. HI hydroiodic acid

7. H2S hydrosulfuric acid

8. HC2H3O2 acetic acid

Practice

9. Write the balanced formula, total ionic and net ionic equations for the acid base neutralization reaction that occurs when aqueous sulfuric acid is mixed with aqueous potassium hydroxide

(put answer on front whiteboard)

Properties of Acids and Bases

Acids Bases

Taste sour Taste bitter

Feel wet Feel slippery

Turn litmus RED Turn litmus BLUE

Conduct electricity Conduct electricity

React with most metals Do NOT react with most metals

Contain more H+ than OH- Contain more OH- than H+

pH between 0 and 7 pH between 7 and 14

strong acid + strong base salt + H2O

Arrhenius acids and bases

Acid: compound containing H that ionizes to yield H+ in solution

HCl(g) H+

(aq) + Cl-(aq)

HCl(g) + H2O(l) H3O+

(aq) + Cl-(aq)

Base: compound containing OH that ionizes to yield OH- in solution

NaOH(s) Na+

(aq) + OH-(aq)

*Note: Every Arrhenius acid/base is also a Brønsted-Lowry acid/base.

H2O

H2O

Autoionization of Water

In pure water :

[H3O+] = 1.0 x 10-7 M AND [OH-] = 1.0 x 10-7 M

If we add acid [H3O+] increases and [OH-] decreases.

[H3O+] = 1.0 x 10-4 M [OH-] = 1.0 x 10-10 M

If we add base, the reverse is true:

[H3O+] = 1.0 x 10-10 M [OH-] = 1.0 x 10-4 M

What is the product of [H3O+] x [OH-] in each case?

H2O + H2O H3O

++ OH-

The pH Scale

pOH = - log [OH-]

= - log (1.0 x 10-7)

= -(-7)

= 7

pH = - log [H+]

= - log (1.0 x 10-7)

= -(-7)

= 7

Pure Water

basis of neutral pH 7:[H+] = [OH-]

Concentration, pH and pOH(for strong acids and bases)

Concentration is given in terms of molarity (M)

Concentration of H+ = [H+] = = 0.0100 M

In scientific notation: [H+] = 1.00 x 10-2 M

Find pH: pH = -log[1.00 x 10-2 M] pH = 2

Find pOH: pH + pOH = 14 pOH = 12

Find [OH-]: [OH-] = 10-pOH = 10-12 [OH-] = 1.00 x 10-12 M

0.0100 moles H+

L solution

Converting between Concentration and pH

pH pOH[H+] [OH-]10-pOH

-log[H+ ]

14-pH

pHpOH [H+][OH-] 10-pH

-log[OH- ]

14-pOH

1.00 x 10-4 M 4 10 1.00 x 10-10 M

1.00 x 10-11 M 11 3 1.00 x 10-3 M

Practice

pH + pOH = 14; pH = -log[H+]; pOH = -log[OH-]

When pH = 2

[H+] = _____________M

pOH = ____________

[OH-] = ____________M

When pOH = 8

[OH-] = ___________ M

pH = _____________

[H+] = ____________ M

[H+] = 1.0 x 10-3 M What is the [OH-]?

More Practice (HW)

1. What is the pH of a solution with a [H+] of 10-8 M?

2. What is the pOH of a solution with a [OH-] of 10-11 M?

3. What is the pH of a solution with a [OH-] of 10-2 M?

4. What is the pOH of a solution with a [H+] = 10-5 M?

5. Which is more acidic, a solution with a pH of 6 or one

with a pH of 9?

6. Which is more basic, a solution with a pOH of 7 or one

with a pOH of 12?

7. Which is more acidic, a solution with a pH of 5 or one

with a pOH of 10?

8. Which is more basic, a solution with a pH of 8 or one

with a pOH of 12?

More Practice

1. What is the pH of a solution with a [H+] of 10-8 M? 8

2. What is the pOH of a solution with a [OH-] of 10-11 M? 11

3. What is the pH of a solution with a [OH-] of 10-2 M? 12

4. What is the pOH of a solution with a [H+] = 10-5 M? 9

5. Which is more acidic, a solution with a pH of 6 or one

with a pH of 9? pH of 6

6. Which is more basic, a solution with a pOH of 7 or one

with a pOH of 12? pOH of 7

7. Which is more acidic, a solution with a pH of 5 or one

with a pOH of 10? pOH of 10

8. Which is more basic, a solution with a pH of 8 or one

with a pOH of 12? pH of 8

More Practice

9. Stomach contents can have a pH of 3.

Are stomach contents acidic, basic or neutral?

10. Pure water has a pOH of 7. Is pure water acidic, basic or neutral?

11. Normal rain has a pH of approximately 6. Is normal rain strongly acidic, slightly acidic, neutral, slightly basic, or strongly basic?

12. Acid precipitation is often a problem in industrialized areas.

What might you expect the pH of acid rain to be?

More Practice

9. Stomach contents can have a pH of 3. Are stomach contents acidic, basic or neutral? acidic

10. Pure water has a pOH of 7. Is pure water acidic, basic or neutral? neutral

11. Normal rain has a pH of approximately 6. Is normal rain strongly acidic, slightly acidic, neutral, slightly basic, or strongly basic?

slightly acidic

12. Acid precipitation is often a problem in industrialized areas.

What might you expect the pH of acid rain to be? < 6

Warm up

1. Write formulas for the following acids:

a) hydroiodic acid

b) chlorous acid

c) chloric acid

d) perchloric acid (Honors)

e) hypochlorous acid (Honors)

f) phosphoric acid

g) phosphorous acid

Warm up

1. Write formulas for the following acids:

a) hydroiodic acid HI

b) chlorous acid HClO2

c) chloric acid HClO3

d) perchloric acid HClO4 (Honors)

e) hypochlorous acid HClO (Honors)

f) phosphoric acid H3PO4

g) phosphorous acid H3PO3 (Honors)

Warmup

What is the pH of a solution of nitric acid (strong acid) that has a concentration of 10-4 M?

What is its pOH?

Concentration of OH-?

Warmup

What is the pH of a solution of nitric acid (strong acid) that has a concentration of 10-4 M?

4

What is its pOH?

10

Concentration of OH-?

10-10 M

Acid-base Indicators

• Acid-base indicator = a weak acid or base that

undergoes dissociation in a known pH range.

• In this range, the acid (base) is a different

color from its conjugate base (or acid).

• Universal indicator (UI) = a mixture of

indicators that shows a range of colors over a

wide range of pH values

Intro to pH Serial Dilution Lab

• Overview: you will create a pH scale (1 to 14) by serial dilutions, then test acid-base indicators.

Serial Dilutions

1 drop 1 M HCl + 9 drops dH2O = 10X dilution

i.e. 1M 0.1 M, which is pH = 1

1 drop 0.1 M HCl + 9 drops dH2O = 10X dilution

i.e. 0.1M 0.01 M 10-2 M, which is pH = 2

Intro to pH Serial Dilution Lab

Safety: apron and goggles

Complete the pre-lab questions on the first page before you go into lab

Work on your own

Intro to pH Serial Dilution Lab

Begin with UI, then choose at least two other acid-base indicators to test.

Use dH2O dropper bottle for the 9 drops of water per well.

Be sure to rinse pipet with dH2O between dilutions.

Collect this dH2O into a beaker from the carboys by the windows.

Rinse and dry wellplates/spot plates between runs (use dH2O).

Neutralization Reactions

When a strong acid reacts with a strong base, the net ionic equation is…

HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)

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Neutralization Reactions

When a strong acid reacts with a strong base, the net ionic equation is…

HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)

H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq)

Na+ (aq) + Cl- (aq) + H2O (l)

© 2009, Prentice-Hall, Inc.

Neutralization Reactions

When a strong acid reacts with a strong base, the net ionic equation is…

HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)

H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq)

Na+ (aq) + Cl- (aq) + H2O (l)

H+ (aq) + OH- (aq) H2O (l)

© 2009, Prentice-Hall, Inc.

Titration

Titration is an

analytical

technique in

which one can

calculate the

concentration

of a solute in

a solution.

© 2009, Prentice-Hall, Inc.

Titration

= A method of volumetric analysis in which a volume of one

reagent is added to a known volume of another reagent

slowly from a buret until an end point is reached. If

one of the solutions has a known concentration, the

concentration of the other can be calculated, via

stoichiometry.

© 2009, Prentice-Hall, Inc.

Titration

Standard solution = reagent solution of knownconcentration

Titrant = reagent solution of unknownconcentration

Equivalence point = the point at which stoichiometrically equivalent quantities are brought together

End point = color change (v. close to equivalence point)

© 2009, Prentice-Hall, Inc.

Change in appearance of a solution containing

phenolphthalein as base indicator

© 2009, Prentice-Hall, Inc.

Titration

© 2009, Prentice-Hall, Inc.

Example Titration

Predict the number of mL of ~0.10 M NaOH needed to

neutralize 10.0 mL of 0.25 M HCl.

We want to know the exact molarity of the NaOH

solution.

© 2009, Prentice-Hall, Inc.

Titration Practice Problems

Remember: Moles are

central!1. In the titration of 35 mL of liquid drain cleaner

containing NaOH, 50. mL of 0.40 M HCl must be added

to reach the equivalence point. What is the molarity

of the base in the cleaner?

(0.57 M)

© 2009, Prentice-Hall, Inc.

Titration Practice Problems

Remember: Moles are

central!2. A 20.0 mL sample of an HCl solution is titrated with

27.4 mL of a standard solution of Ba(OH)2.

The concentration of the standard is 0.0154 M. What

is the molarity of the HCl?

(0.0422 M)

© 2009, Prentice-Hall, Inc.

Strength of Acids and Bases

Strong acid or base – ionizes/dissociates completely in water

[H+] or [OH-] = conc. of acid or base. e.g. HCl, NaOH.

5 units of acid – 5 out of 5 dissociated

H+ Cl- H+ Cl- H+ Cl- H+ Cl- H+ Cl-

Weak acid or base – ionizes/dissociates only partially in water

[H+] or [OH-] < conc. of acid or base. e.g. HC2H3O2, NH35 units – only 1 out of 5 dissociated

HC2H3O2 HC2H3O2 HC2H3O2 HC2H3O2 H+ C2H3O2

-

Practice

The diagrams below represent aqueous

solutions of three acids (HX, HY, and HZ)

with water molecules omitted for clarity.

Rank them from strongest to weakest.

© 2009, Prentice-Hall, Inc.

Strengths of Acids and Bases

Strong concentrated

Weak dilute

A concentrated weak acid (or base) may have the same pH as a dilute strong acid (or base).

Strong vs. Weak Demo

Strong acid:

HCl + H2O Cl- + H3O

+

1.0 x 10-2 M ? M

pH = ?

Weak acid:

HC2H3O2 + H2O ↔ C2H3O2- + H3O

+

1.0 x 10-2 M ? M

pH = ?

Strong base:

NaOH + H2O Na+ + OH-

1.0 x 10-2 M ? M

pH = ?

Weak base:

NH3 + H2O ↔ NH4+ + OH-

1.0 x 10-2 M ? M

pH = ?

Strong and Dilute vs. Weak and Concentrated

Acids:

Strong HCl Weak HC2H3O2 Weak HC2H3O2

Dilute Dilute Conc 100 x

0.01 M 0.01 M 1M

pH = pH = pH =

Bases:

Strong NaOH Weak NH3 Weak NH3

Dilute Dilute Conc 100 x

0.01M 0.10 M 1M

pH = pH = pH =

Warmup

Compare strong acids with weak acids. Use

concentration, extent of ionization, and pH in your

answer.

Warmup

Compare strong acids with weak acids. Use concentration,

extent of ionization, and pH in your answer.

Strong acids ionize completely in water, so the concentration

of H+ is the same as the compound itself. A weak acid of

equal concentration (molarity) will have a lower

concentration of H+, and thus a higher pH.

What do you think?

Table salt

Vinegar

Rubbing alcohol

Window Cleaner

Distilled water

Lemon juice

Soap

Drain cleaner

Applesauce

Blood

Are the following acidic, basic or neutral?

What is the difference between a strong acid and a concentrated acid?

A weak acid and a dilute acid?

Brønsted-Lowry Acids and Bases (1923)

Acid: H+ (proton) donor

Base: H+ (proton) acceptor

HCl + H2O H3O+ + Cl-

acid base conjugate conjugate

acid base

Brønsted-Lowry Acids and Bases (1923)

NH3 + H2O D NH4+ + OH-

ammonia water ammonium ionhydroxide ion

(B-L base) (B-L acid) (B-L acid) (B-L base)

base acid conjugate acid conjugate base

Conjugate Acid-Base Pairs

Conjugate acid = species produced when a base accepts a hydrogen ion from an acid

Conjugate base = species that results when an acid donates a hydrogen ion to a base

Identify the conjugate acid-base pairs:

HClO + H2O D ClO- + H3O

+

HS- + H2O D H2S + OH-

HPO42- + H2O D H2PO4

- + OH-

HPO42- + H2O D PO4

3- + H3O+

An amphoteric compound is able to act as either an

acid or a base. Which compounds in the above

equations are amphoteric?