08AcidsandBasesP2properties.pptx

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8.2 Properties of acids and Bases

Base and Alkalis

A base is any metal oxide or hydroxide.

Hence, a base contains either oxide ions, O2–, or hydroxide ions, OH–.

For example: Na₂O, ZnO, CuO, Mg(OH)₂ and Al(OH)₃

An alkali is a base that is soluble in water. It produces hydroxide ions when dissolved in water.

Some common examples of alkalis:

• _{Sodium hydroxide NaOH(aq)}__Na+_{+ OH}

-• _{Potassium hydroxide KOH (aq)}_K+_{+ OH}

-• _{Calcium hydroxide Ca(OH)}

2 (aq)  Ca2+ + 2OH

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-Acids and bases can be distinguished using indicators

Indicators: Are used to determined whether a solution is Acidic ore base

Acids react with metals, bases and carbonates to from salts 1 Acids + Metal  Salt + Hydrogen

2HCl (aq)+ Zn(s)  ZnCl₂(aq) + H₂(g) H₂SO₄(aq) + Mg(s)  MgSO₄(s) + H₂(g)

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2 Acid + Base  Salt + Water

HCl(aq) + NaOH(aq)  NaCl(aq) + H₂O(l) H₂SO₄(aq) + 2KOH(aq)  K₂SO₄(aq) + H₂O(l) 2HNO₃(aq) + Ca(OH)₂(aq)  Ca(NO₃)₂ +H₂O(l)

CH₃COOH(aq) + NaOH(aq)  NaOOCCH₃(aq) + H₂O(l)

Neutralization reaction used in titration to determine the PH of a solution

3 Acid + Carbonate  Salt + Carbon dioxide

2HNO(aq)₃ + Na₂CO₃(s)  2NaNO₃(aq) + CO₂(g) + H₂O(l) H₂SO₄(aq) + CaCO₃(s)  CaSO₄(s) + CO₂(g) + H₂O(l)

2HCl + CaCO₃ (s) CaCl₂(aq) + CO₂(g) + H₂O(l)

4 Acids + Metal oxide  Salt + water

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HA (aq) + H₂O (l) « H₃O+ _{(aq) + A}-_(aq)

An acid in water will donate a proton to a water molecule

Strong acid: K_ais large, the equilibrium lies far toward products 8.3 Strong and weak acids and 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.

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Weak acid: K_ais small, the equilibrium lies toward reactants

Weak acid: Are much less than 100% Ionized in water HA (aq) + H₂O (l) « H₃O+ _{(aq) + A}-_(aq)

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Strong base: K_bis large, the equilibrium lies toward products B (aq) + H₂O (l) « OH- _{(aq) + BH}+_(aq)

A base in water will receive a proton from a water molecule

Strong base: 100% dissociated in water

NaOH (aq)  Na+ _{(aq) + OH}- _(aq)

common strong bases include KOH, CA(OH)_2, CaO (lime)

CaO

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Weak base: K_bis small, the equilibrium lies toward reactants

Weak base: Are much less than 100% Ionized in water One of the most common weak bases is Ammonia

NH

₃

(aq) + H

₂

O (l)



NH

₄+

(aq) + OH

-

(aq)



+

Electrical conductivity: As strong Acids/bases dissociates more than weak Acids/bases, they conduct better electricity (higher conductivity)

Rate of reactions : Reactions with acids depend on H+_{, therefore they will}

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Strength and concentration are NOT the same!

Strong acid – High concentration Weak acid – High concentration

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Non-Acids

Weak Acids

Strong Acids

Strengths of Acids at 1.0M

10

-8

₁₀

-6

10

-4

₁₀

-2

₁₀

2

10

4

10

6

0

20

40

60

80

100 K

_a

P

er

ce

n

t

D

is

so

ci

at

io

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10

-8

₁₀

-6

10

-4

₁₀

-2

₁₀

2

10

4

10

6

0.01

0.1

1

10

100 K

_a

P

er

ce

n

t

D

is

so

ci

at

io

n

Variation in Acid Strength with Concentration

1M

10

-1

_M

10

-2

M

10

-3

M

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10

6

10

5

10

4

10

3

10

2

10

1

10

-1

10

-2

10

-3

10

-4

10

-5

10

-6

10

-7

10

-8

100%

60%

0%

80%

40%

20%

HA

H

₃

O

+

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Acid/Base Strength is Relative

A

-

B

H

O

H

O

H H

O

H

_O

H

+

-+

Acid Strength

Base Strength

HA

H

₂

O

B

H

A

-H

₃

O

+

BH

+

OH

-H

+

H

-A

-BH

+

HA + B

«

+ BH

+

A

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Cl

-NO

₃

-H

₂

O

OH

-F

-HS

-CN

-NH

₃

O

2-HCO

₃

-H

₂

PO

₄

-S

2-HCl

HNO

₃

H

₃

O

+

H

₂

O

HF

H

₂

S

HCN

NH

₄+

OH

-H

₂

CO

₃

H

₃

PO

₄

HS

-HCl

HNO

₃

H

₃

O

+

Cl

-NO

₃

-H

₂

O

H

₂

O

OH

-HF

F

-H

₂

S

HS

-HCN

CN

-NH

₄+

NH

3

OH

-

O

2-H

₂

CO

₃

HCO

3

-H

₃

PO

₄

H

₂

PO

₄

-A

ci

d

S

tr

en

gt

h

B

as

e S

tr

en

gt

h

HS

-

S

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Water is both an acid AND a base

In water, one water molecule can donate a proton to another

H

O

H

O

H

-

H

+

H

₂

O (l) + H

₂

O (l)

« O

H

-

(aq) + H

3

O

+

(aq)

Autoionization

K

_eq

= [H

₃

O

+

_][OH

-

_{] = K}

w

=

10

-14

at 25

°

C

The value of K

_w

will change with temperature!

In ANY aqueous solution at 25

°

C

[H

3

O

+

] [OH

-

] = 10

-14

When you change one of the concentrations, the other must

change to preserve the equality

If [H

₃

O

+

] > [OH

-

]

_{Solution is acidic}

Solution is neutral

If [H

₃

O

+

] = [OH

-

] = 10

-7

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Hold on….

These numbers that we’re dealing with are pretty small (10

-14

)

Lets put our variables on a base-10 logarithmic scale!

and they vary over a very wide range (10

-14

- 10)!

log

₁₀

(10

-14

_{) = -14}

…while we’re at it, let’s make all of our numbers positive

-log

₁₀

(10

-14

_{) = 14}

Let’s work with -log [H

+

]

This is the PH scale!

pH = -log [H

+

]

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In aqueous solution:

0

2

4

6

7

8

10

12

14

1

10

-14

10

-2

10

-4

10

-6

10

-8

10

-10

10

-12

[H

₃

O

+

]

[OH

-

]

1

10

-14

10

-2

10

-4

10

-6

10

-8

10

-10

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14 1 x 10-14 1 x 10-0 0

13 1 x 10-13 1 x 10-1 1

12 1 x 10-12 1 x 10-2 2

11 1 x 10-11 1 x 10-3 3

10 1 x 10-10 1 x 10-4 4

9 1 x 10-9 1 x 10-5 5

8 1 x 10-8 1 x 10-6 6

6 1 x 10-6 1 x 10-8 8

5 1 x 10-5 1 x 10-9 9

4 1 x 10-4 1 x 10-10 10

3 1 x 10-3 1 x 10-11 11

2 1 x 10-2 1 x 10-12 12

1 1 x 10-1 1 x 10-13 13

0 1 x 100 1 x 10-14 14

7 1 x 10-7 1 x 10-7 7

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The pH of an aqueous solution is 3.85. What is the [H₃O+] of the solution?

pH = -log [H+] so [H+] = 10-pH = 10-3.85 = 1.41 x 10-4 M

Example

Procedure to find pH

1 Find the Molarity of the hydrogen ions, which is the H+_{concentration}

Example: A 0.01 M solution of HCl has a concentration of H+_{ions equal to 0.01 mol/L.}

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Two pH calculation methods:

“Longhand” or “Calculator”

1. “Longhand” method:

a. Write molarity in exponential form.

.01 = 10

-2

b. The logarithm of 10

-2

_{is -2.}

c. The negative of -2 is 2

d. The pH is 2.

(Use for molar concentrations that are in powers of ten:

10

-6

, 10

-12

)

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2a. Method #1 (Casio Classroom calculator):

a. enter molarity (.01) in your calculator: .01

b. press the key that says “log” : read “-2”

c. press the +/- key to change the sign = 2

d. read the pH as 2

2b. Method #2 (Casio fx-3000MS calculator): a. Press the log button

b. Enter the number “.01”

c. Press the “=“ key and read “-2”

d. Change the sign and read the pH as 2

(Use for molar concentrations that are in other than powers of ten.)

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Calculate the pH of 0.10 M HCl

Calculate: pH for [H+] = 1.67•10-5

Exercise

What is the pH of 0.050 M HNO₃?

pH = -log[H₃O+], pH = -log[0.050], pH = 1.3

What is the pH of 3.33•10-2M HCl solution

[H₃O+_{] =3.33•10}-2_{M, pH = 1.48}

pH = -log[H+], pH = -log[0.1], pH = 1

pH = -log[H₃O+], pH = -log[_1.67•10-5], pH = 4.78

What is the pH of 5.68•10-8_{M HNO} 3?