Acids-Bases I.pptx

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Acids & Bases

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A. Properties

 electrolytes _ electrolytes

 turn litmus red

 sour taste

 react with metals

to form H₂ gas

 slippery feel

 turn litmus blue

 bitter taste

ChemASAP

 vinegar, milk, soda,

apples, citrus fruits

 ammonia, lye,

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B. Definitions

 Arrhenius - In aqueous solution…

HCl

+ H

₂

O



H

₃

O

+

+ Cl

–

• Acids form hydronium ions (H₃O+)

H

H H H

H

Cl O O Cl

–

+

(4)

B. Definitions

 Arrhenius - In aqueous solution…

• Bases_{form hydroxide ions (OH}-)

NH

₃

+ H

₂

O



NH

₄+

+

OH

-H

H

H H H

H

N O N + O –

H

H H

(5)

B. Definitions

 Brønsted-Lowry

HCl + H

₂

O



Cl

–

+ H

3

O

+

• Acids _{are proton (H}+) donors.

• Bases_{are proton (H}+) acceptors.

conjugate acid

conjugate base

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B. Definitions

H

₂

O + HNO

₃



H

₃

O

+

+ NO

3–

CB

CA

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B. Definitions

 Amphoteric - can be an acid or a base.

NH

₃

+ H

₂

O



NH

₄+

+ OH

-CA

CB

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B. Definitions

F

-H

₂

PO

₄

-H

₂

O

HF

H

₃

PO

₄

H

₃

O

+

 _{Give the conjugate base for each of the following:}

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B. Definitions

Br

-HSO

₄

-CO

₃

2-HBr

H

₂

SO

₄

HCO

₃

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B. Definitions

 Lewis

• Acids _{are electron pair acceptors.} • Bases_{are electron pair donors.}

Lewis

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C. Strength

 Strong Acid/Base

• _{100% ionized in water} • _{strong electrolyte}

- +

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C. Strength

 Weak Acid/Base

• _{does not ionize completely} • _{weak electrolyte}

- +

HF

CH3COOH H3PO4

H₂CO₃ HCN

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D. Ionization of Water

H

₂

O + H

₂

O H

₃

O

+

+ OH

-K

_w

= [H

₃

O

+

][OH

-

] = 1.0



10

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D. Ionization of Water

 Find the hydroxide ion concentration of 3.0  10-2 M HCl.

[H₃O+][OH-] = 1.0  10-14 [3.0  10-2][OH-] = 1.0  10-14

[OH-] = 3.3  10-13 M

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pH = -log[H

₃

O

+

]

E. pH Scale

0

7

INCREASING

ACIDITY NEUTRAL

INCREASING BASICITY

14

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E. pH Scale

pH of Common Substances

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E. pH Scale

pH = -log[H

₃

O

+

]

pOH =

-log[OH

-

]

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E. pH Scale

 What is the pH of 0.050 M HNO₃?

pH = -log[H₃O+]

pH = -log[0.050]

pH = 1.3

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E. pH Scale

 What is the molarity of HBr in a solution that has a pOH of 9.6?

pH + pOH = 14 pH + 9.6 = 14

pH = 4.4

Acidic

pH = -log[H₃O+]

4.4 = -log[H₃O+]

-4.4 = log[H₃O+]

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F. pH of Weak Acids/Bases

 Weak Acids/Bases

 Calculations are done the same way except that you must do an ICE chart equilibrium problem to get the [H+] or [OH-]

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F. pH of Weak Acids/Bases

 What is the pH of a 1.00 M solution of HF?

 HF = H+ + F - 0.10 0 0  -x +x +x  1.00-x x x  [H+]= x= 0.025M

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 Does the “easy” way work?

 5% rule…is our approximation valid to 5%?

 If: x/[HA] * 100 ≤%5, then the

approximation is valid; if not, then you have to use equation solver…

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Percent Dissociation

(ionization)

Percent Dissociation

(ionization)

 % dissociation = amt dissociated x 100 initial concen.

Example: the amount of 1.00M HF that dissociated was 0.025M, what is the % dissociation?

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 Let’s check…

 0.025/1.00*100 =

 2.5%, so our approximation is valid.  What is the pH? -log(0.025)

 pH= 1.60

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You Try

Calculate the pH of a 0.100M aqueous solution of hypochlorous acid (HClO). K_a= 3.5x10-8

pH = 4.23

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G. Calculating the pH of a

Mixture of Acids

G. Calculating the pH of a

Mixture of Acids

 The acid with the larger K_a is the

stronger acid and will be the dominate producer of [H+].

 Of the following which will dominate?

 HCN K_a= 6.2x10-10

 HNO₂ K_a= 4.0x10-4

 H₂O K_a= 1.0x10-14

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G. You try…

 Calculate the pH of a solution that

contains 1.00M HCN and 5.00M HNO₂.

 pH= 1.35

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G. Further Thinking…

 How could we find the [CN-]?

 [CN-]= 1.4x10-8M

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14.8 Acid-Base Properties

of Salts

 Salt: another name for ionic compound

• _{When dissolved in water it breaks}

apart into ions, which move about independently.

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Salts that Produce Basic

Solutions

Salts that Produce Basic

Solutions

 What are the major species in a 1.0M aqueous solution of sodium acetate?  Na+, C₂H₃O₂-1, and H₂O

 Which has either acidic or basic properties?

 Write the equation for the equilibrium which occurs.

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Con’t

 C₂H₃O₂-

(aq)+H2O HC2H3O2(aq) +OH-1(aq)

 Determine the K_b from the K_a and set up the

equilibrium expression. (K_a * K_b= K_w)

• K_b= 5.6x10-10

 _{Calculate the [OH}-1]

• _{= 2.4x10}-5M

 _{Calculate the pH}

• _9.37

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You Try…

 Calculate the pH of a 0.30M NaF solution. The K_a for HF is 7.2x10-4.

 pH= 8.31

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Salts as Weak Acids

 Calculate the pH of a 0.10M NH₄Cl solution. The K_b for NH₃ is 1.8x10-5.  Identify the species in the solution.

Which is acidic/basic?

 Write the equation for the reaction.  Set up the equilibrium expression.

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Con’t

 Plug info into equilibrium expression  Solve for [H+]

• _7.5x10-6M  Calculate pH

• _5.13

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You Try…

 Calculate the pH of a 0.010M AlCl₃. The K_a value for Al(H₂O)+6 is 1.4x10-5.

 pH= 3.43

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The Acid-Base Properties

of Salts

The Acid-Base Properties

of Salts

 K_a> K_b, pH< 7, acidic

 K_a< K_b, pH> 7, basic

 K_a= K_b, pH= 7, neutral

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Predictions…

 Acid, Base or Neutral?

A. Ammonium acetate B. Ammonium cyanide C. Aluminum sulfate

a. Neutralb. basic c. acidic

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Study…

 Make sure you study the properties summarized on p. 700.

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14.9 Effect of Structure

on Acid-Base Properties

 Stronger bonds = weaker acid  Higher polarity = stronger acid

• _{Polarity increases as the difference in}

electronegativity increases.

 Why is it that HF is a weak acid?

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14.9 Effect of Structure

 Oxyacids: acids containing oxygen

• _{Strength increases as the number of}

oxygens increase

• oxygen is very electronegative and

pulls the electrons away from the other atom and weakens the bond.

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14.10 Acid-Base Properties

of Oxides

 When covalent oxides dissolve in water, acidic solutions form. Known as acidic oxides.

 SO₂ (g)+ H₂O (l) H₂SO₃ (aq)

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of Oxides

 When ionic oxides dissolve in water, basic solutions form. Known as basic oxides.

 CaO (s) + H₂O (l)  Ca(OH)₂ (aq)