Chapter 17 – Acids and Bases

Properties of Acids:

1. Taste Sour

2. Cause certain dyes to change color

3. Acids are neutralized by bases to form neutral salt solutions

4. Acids react with carbonates to form CO 2, salt and water.

5. Form electrolyte solutions in water.

6. Contain H and something else.

Properties of bases.

1. Taste bitter

2. Feel slippery

3. Cause certain dyes to change color.

4. Form electrolyte solutions in water.

5. React with acids to form neutral solutions of salts .

6. All metal hydroxides are bases. Not all bases are metal hydroxides.

Definitions:

Svante Arrhenius Definition:

Acid: produces H +(aq) ions in water

Base: produces OH -(aq) ions in water

Na2CO3 neutralizes acids, but doesn’t contain OH - ions. Need a new definition.

Bronsted – Lowry Definition:

Acid: Hydrogen ion (proton) donor

An acid and its conjugate base differ by 1 hydrogen ion. A base and its conjugate acid differ by 1 hydrogen ion.

Problem: Write the conjugate base of: (subtract H +)

HFNH4

+

H2OH3PO4H2PO4

-

Problem: Write the conjugate acid of the following bases:(add H+)

OH-

NH3HPO4

-2

HCO3-

Base: Hydrogen ion (proton) acceptor

The products in this definition are not always � salt + water

Is water an acid or base?

Problem: Write an acid/base equation for: (acid) (base)HCl + H2O �

Amphoteric: A substance that can act like an acid or a base

(base) (acid)NH3 + H2O �

Write acid/base equations for the following reactan ts:

H2SO4 + H2O �

CH3NH2 + H2O �

Strength of Acids:

Strength is measured by an acids ability to donate H+ ions.

Strong Acid Properties:1. Good electrolyte

2. Completely ionize in water

3. Big equilibrium values

4. HClO4, HI, HCl, HBr, HNO 3, H2SO4 are the strong acids.

Weak Acid Properties:1. Poor Electrolytes

2. Don’t completely ionize in water

3. Small equilibrium values

4. All other acids are weak KHF = 7 x 10-4

HCN = 4 x 10-10

H2SO4 is both a strong and weak acid, or a diprotic acid.

Strong Base Properties:

1. Good electrolyte2. Soluble in water, producing lots of OH -

3. Alkali metal hydroxides, Ca(OH) 2, Sr(OH)2 and Ba(OH) 2 are the strong bases.

Weak Base Properties:

1. weak electrolyte2. Produce very little OH - in water3. All other bases are weak, and have small equili brium constants.

Autoionization of water:

H2O(l) + H2O(l) ↔ H3O+(aq) + OH-

(aq)

b) 2.5 x 10 -4 M H+

c) 10.0 M H+

Is this solution acidic, basic or neutral? [H +] = [OH -] = 0.0010

Calculate the [H +] and the [OH -] in the following solutions, and state whether the solution is acidic or basic.

a) 1.0 x 10-5 M OH-

If [H+] = [OH -] the solution is neutral

If [H+] > [OH -] the solution is acidic

If [H+] < [OH -] the solution is basic

The p scale…pH and pOH

( where p means (-1)log )

pH = (-1) log [H +] pOH = (-1) log [OH -]

1) Problem: [H +] = 1 x 10 -7 Determine pH, then pOH

Is this solution acidic, basic or neutral?

2) Problem: Calculate the [H +] , [OH -] , pH and pOH of a .10 M H + solution.

Is this solution acidic, basic or neutral?

3) Problem: A solution has [OH -] = .020 M Calculate the [H 3O+], [OH -], pH and pOH.

Is this solution acidic, basic or neutral?

What is the sum of pH + pOH in problem 1 – 3?

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

pOH 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Acidic Basic

Problem: Coke has a pH of 3.15 Calculate the pOH , [H3O+] and [OH -]

pH of some commonsubstances

Strong Acid and Base pH calculations - (recall that strong acids and basesionize or dissociate 100% in water.)

1. Problem: Determine the pH of a 0.020 M HCl Sol ution

2. Problem: Determine the pH of a 3.2 x 10 -4 M HNO3 solution.

3. Problem: Determine the pH of a .25 M NaOH solu tion

Weak Acid and base pH calculations:

Write an equation for the reaction of acetic acid (HC2H3O2) in water.

Determine the pH of a 0.20 M HC 2H3O2 w/ Ka = 1.8 x 10-5

1. Problem: Determine the pH of a .35 M HOCl solut ion with Ka = 3.5 x 10 -8

Weak bases have the same type of reaction with wate r:

NH3(aq) + H2O ↔ complete the equation

Kb = ?

3. Problem: Calculate the pH of a 0.75 M NH 3 solution with K b = 1.8 x 10-5

2. Write an equation of the weak base, methylamine , CH3NH2, added to water.

1. Determine the pH of a .13 M caffeine solution, a weak base (C 8H10N4O2) where

Kb = 5.8 x 10-4

Buffer – a solution that a) resists a change in pH when an acid and a base are added to the

buffered solution.

b) contains either : 1) weak acid and salt of tha t acid (conjugate base)2) weak base and the salt of that base (conjugate acid)

Are the following solutions buffers?

1. H2CO3 and NaHCO3

2. H2CO3 and Na2CO3

3. HCl and KCl

4. NaH2PO4 and Na2HPO4

Problem: A buffer consists of HC 2H3O2 and NaC2H3O2

What component of buffer will react with added HCl?

Blood is buffered to a pH = 7.40. If pH drops belo w 7.3 or rises above 7.5, this will be fatal within a short period of t ime.

Blood buffer system is mainly H 2CO3 and HCO3-

CO2(lungs) ↔ CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- ↔ HCO3

-(urine)

NaOH?

Problem: A buffer consists of an aqueous solution of HF and NaF.

Which part of the buffer would be neutralized if Na OH were added to the buffer?

Which part of the buffer would be neutralized if HC l were added to the buffer?

A buffer contains both an acid and a base, but this combination of acid and basedoesn’t neutralize itself, but will neutralize any other added acid or base.

Problem: 21.0 mL .20 M H 3PO4 are titrated with 17.0 mL Ca(OH) 2Determine the molarity of Ca(OH) 2

Titration: Technique used to determine molarity of a substance.Endpoint – signaled by a color change of an indicato r, when an acid and a base have neutralized each other .

Acid Anhydride – a non-metallic oxide

e.g. CO2N2O5SO3

Acid Anhydride + Water → Acid

CO2 + H2O →

SO3 + H2O →

Acid Rain – acid anhydrides combine with water moist ure, acidic rain drops arethe result.

Sulfur oxide from coal burning power plants is a ma jor contributor to acid rain

The effects of acid rain.

Teeth Chemistry:

Tooth Enamel Ca 5(PO4)3OH(s) + H+(aq) → H2O + soluble tooth enamel (aq)