Acid-Base Titration and pH

Chapter 16

chemistry chapter 16 2

Self-Ionization of water Two water molecules produce a

hydronium ion and a hydroxide ion by transfer of a proton

chemistry chapter 16 3

Pure water Concentrations of hydronium and

hydroxide ions of 1.0 x 10-7 mol/L at 25 °C.

chemistry chapter 16 4

Expressing concentrations Brackets indicate concentration in

mol/L [H3O+] means

Hydronium ion concentration in moles per liter

or Molar hydronium ion concentration

chemistry chapter 16 5

Ionization constant of water

1.0 x 10-14 M2 or (mol/L)2

Constant over ordinary room temperatures

For pure water or dilute aqueous solutions

OHOHKw 3

chemistry chapter 16 6

Solutions Neutral

[H3O+]=[OH-] Acidic

[H3O+]>[OH-] Basic

[H3O+]<[OH-]

chemistry chapter 16 7

Strong bases Ionize completely in solution Molar concentration of hydroxide

ions is the same as the molarity of the solution times the subscript of hydroxide.

Example: A 1.0 x 10-3 M LiOH solution has [OH-] of 1.0 x 10-3 M

Example: A 1.0 x 10-3 M Ca(OH)2 solution has [OH-] of 2.0 x 10-3 M

chemistry chapter 16 8

Strong Acids Ionize completely in solution Molar concentration of hydronium ions

is the same as the molarity of the solution times the subscript of hydrogen.

Example: A 1.0 x 10-4 M HCl solution has [H3O+] of 1.0 x 10-4 M

Example: A 1.0 x 10-4 M H2SO4 solution has [H3O+] of 2.0 x 10-4 M

chemistry chapter 16 9

Using Kw

If you know the concentration of hydronium or hydroxide ions, you can use Kw to find the concentration of the other ion.

See page 484

OHOHKw 3

chemistry chapter 16 10

pH The negative of the common

logarithm of the hydronium ion concentration

OHpH 3log

chemistry chapter 16 11

pOH The negative of the common

logarithm of the hydroxide ion concentration

OHpOH log

chemistry chapter 16 12

relationship0.14 pOHpH

chemistry chapter 16 13

chemistry chapter 16 14

Discuss What is the concentration of hydronium

and hydroxide ions in pure water at 25 °C?

For each of the following properties, is the solution acidic or basic? [H3O+] = 1.0 x 10-3 M [OH-] = 1.0 x 10-4 M pH = 5.0 pH = 8.0

chemistry chapter 16 15

Acid-Base indicators Used to obtain an approximate

value for pH. Compounds whose colors are

sensitive to pH. Weak acids or weak bases

chemistry chapter 16 16

Transition interval The pH range over which an

indicator changes color See page 495

chemistry chapter 16 17

Universal indicators Use a combination of several

different indicators. pH paper has been soaked in a

universal indicator.

chemistry chapter 16 18

pH meters Used to find the exact pH Measures the voltage between two

electrodes placed in solution. Changes with hydronium ion

concentration

chemistry chapter 16 19

Titration The controlled addition and

measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration.

chemistry chapter 16 20

Equivalence point When the two solutions used in a

titration are present in chemically equivalent amounts Not always neutral

chemistry chapter 16 21

End point The point in a titration at which an

indicator changes color. Can be used to find equivalence

point. If the indicator changes color at the

equivalence point

chemistry chapter 16 22

Strong acid titrated with strong base

chemistry chapter 16 23

Weak acid titrated with strong base

chemistry chapter 16 24

Discuss P. 503 section review 1 and 2.

chemistry chapter 16 25

Standard solution The “known” solution Its concentration is known

precisely

chemistry chapter 16 26

Primary standard Highly purified solid compound Used to check the concentration of

the known solution

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Titration process See pages 500 - 501

chemistry chapter 16 28

Calculating the unknown concentration1. Write the balanced chemical

equation.2. Determine the moles of the

known solute.3. Determine the moles of the

unknown solute.4. Determine the molarity of the

unknown solution.

chemistry chapter 16 29

Example A 25.00 mL sample of a solution of

RbOH is neutralized by 19.22 mL of a 1.017 M solution of HBr. What is the molarity of the RbOH solution?

0.7820 M

chemistry chapter 16 30

You try If 29.96 mL of a solution of Ba(OH)2

requires 16.08 mL of a 2.303 M solution of HNO3 for complete titration, what is the molarity of the Ba(OH)2 solution?

0.6182 M

chemistry chapter 16 31

You try You have a 0.83 M vinegar

solution. You are going to titrate 20.00 mL of it with a 0.519 M NaOH solution. At what volume of added NaOH solution would you expect to see an end point?

37 mL