Auto-ionization of Water

Auto- Auto -ionization of Water ionization of Water

This is the fundamental concept of This is the fundamental concept of

all acid

all acid--base chemistrybase chemistry

Auto- Auto - ionization of Water ionization of Water

Q:Q: But how often But how often does this happen?

does this happen?

In pure water, how much In pure water, how much of it is water and how of it is water and how

much is ions?

much is ions?

2H

2H₂₂O O  HH₃₃OO⁺⁺ + + OH OH ^–– Hydronium ion

Hydronium ion hydroxide ionhydroxide ion

Auto

Auto- -ionization of Water ionization of Water

A:

A: In pure water, the In pure water, the concentration of H concentration of H₃₃OO^{+ +} is is

1.0 x 1.0 x ^1010--77M.M.

That That’’s onlys only 0.0000001 M ! 0.0000001 M ! In pure water, the concentration of OH

In pure water, the concentration of OH^--is alsois also1.0 x 1.0 x ^1010--77M.M.

2H

2H₂₂O O  HH₃₃OO⁺⁺ + + OH OH ^––

In pure water, In pure water,

[H

[H₃₃OO⁺⁺]] = = [OH[OH^--]]

Hydronium Ion Concentration

Hydronium Ion Concentration = = Hydroxide Ion ConcentrationHydroxide Ion Concentration

Auto

Auto- - ionization of Water ionization of Water

In

In pure waterpure water, the , the concentration of H concentration of H₃₃OO^{+ +} is is

1.0 x 1.0 x ^1010--77M.M.

pH = 7.00 pH = 7.00 What happens if I add some more H What happens if I add some more H₃₃OO⁺⁺?? Let

Let’’s increase the concentration to s increase the concentration to 1.0 x 1.0 x ^10-10-66M M that

that’’s 0.000001 M Hs 0.000001 M H₃₃OO⁺⁺ ……. now the . now the pH = 6.00pH = 6.00 Now,

Now, [H[H₃₃OO⁺⁺]] > > [OH[OH^--]]

Hydronium Ion Concentration

Hydronium Ion Concentration >> Hydroxide Ion ConcentrationHydroxide Ion Concentration

Auto- Auto -ionization of Water ionization of Water

In

In pure waterpure water, the , the concentration of H concentration of H₃₃OO^{+ +} is is

1.0 x 1.0 x ^1010--77M.M.

pH = 7.00 pH = 7.00 What happens if I add some more H What happens if I add some more H₃₃OO⁺⁺??

Let’Let’s increase the Hs increase the H₃₃OO⁺⁺concentration to 1.0 x concentration to 1.0 x ^10-10-55MM (that

(that’’s 0.00001 M Hs 0.00001 M H₃₃OO⁺⁺)…)…. now the . now the pH = 5.00pH = 5.00

Auto- Auto - ionization of Water ionization of Water

In

In pure waterpure water, the , the concentration of H concentration of H₃₃OO^{+ +} is is

1.0 x 1.0 x ^1010--77M.M.

pH = 7.00 pH = 7.00 What happens if I add some more H What happens if I add some more H₃₃OO⁺⁺??

LetLet’’s increase the Hs increase the H₃₃OO⁺⁺concentration to 1.0 x concentration to 1.0 x ^10-10-44MM (that

(that’’s 0.0001 M Hs 0.0001 M H₃₃OO⁺⁺))……. now the . now the pH = 4.00pH = 4.00

Auto- Auto -ionization of Water ionization of Water

In

In pure waterpure water, the , the concentration of H concentration of H₃₃OO^{+ +} is is

1.0 x 1.0 x ^1010--77M.M.

pH = 7.00 pH = 7.00 What happens if I add some more H What happens if I add some more H₃₃OO⁺⁺?? Let

Let’’s increase the Hs increase the H₃₃OO⁺⁺concentration to 1.0 x concentration to 1.0 x ^10-10-33MM (that

(that’’s 0.001 M Hs 0.001 M H₃₃OO⁺⁺))……. now the . now the pH = 3.00pH = 3.00

[H[H₃₃OO⁺⁺]] > > [OH[OH^--]]

Hydronium Ion Concentration

Hydronium Ion Concentration >> Hydroxide Ion ConcentrationHydroxide Ion Concentration

pH pH = a measure of how acidic or

ACIDS BASES

The Nature of Acids and The Nature of Acids and

Bases Bases

  pH = - pH = - log [H log [H _{3 3} O O ^{+ +} ] ]



 pH = - pH = - log [H log [H ^{+ +} ] ]

…where … where [

O

] means the

concentration

of Hydronium Ions of

.

…

…where [H where [H

] is a simplification of what ] is a simplification of what really exists, [H

really exists, [H

O O

] ions. ] ions.

pH and hydronium ions pH and hydronium ions





pH means the power of hydronium pH means the power of hydronium



The amount of H The amount of H

O O

in a substance in a substance determines the acidity.

determines the acidity.



The amount of OH The amount of OH

determines the determines the basisity

basisity. .

pH equation pH equation





To calculate pH: To calculate pH:

pH =

pH = - - log[H log[H

O O

] ] What is a

What is a logarithm logarithm? ? On the Ti

On the Ti- -83, push 83, push - - log,then the log,then the number and you will get the pH.

number and you will get the pH.

Round to .1 place. NO UNITS!!

Round to .1 place. NO UNITS!!  

Indicators Indicators





There are many kinds of acid/base There are many kinds of acid/base indicators.

indicators.





One of these is One of these is phenolphthalein

which which turns at about a pH of 8.

turns at about a pH of 8.



It is It is CLEAR in acids and pink in acids and

in bases. in bases.

How Indicators Work How Indicators Work





Indicators are substances that reflect one Indicators are substances that reflect one color of light in acidic solutions and a color of light in acidic solutions and a different color in basic solutions.

different color in basic solutions.

Various indicators, basic solutions on left and acidic solutions on right.

Indicators, Continued Indicators, Continued

Different indicators react Different indicators react to different levels of to different levels of acidity.

acidity.



Different indicators Different indicators display different colors.

display different colors.

Not all indicators react Not all indicators react the same way to identical the same way to identical acid or base solutions.

acid or base solutions.

Acids Acids or or bases

bases cause cause the

the indicator indicator molecule molecule to to

change change shape and shape and reflect a reflect a different color different color

of light.

of light.

Titration Titration

Titration Titration

= A procedure for determining the

= A procedure for determining the

concentration

of a solution. of a solution.

Acid

Acid- -Base Titration Base Titration

= A titration that uses an acid

= A titration that uses an acid- -base base neutralization reaction.

neutralization reaction.

Acid

Acid - - Base Titration Base Titration

•• We neutralize a solution of unknown concentration with a We neutralize a solution of unknown concentration with a solution of known concentration.

solution of known concentration.

•• Add acid to base, or base to acid Add acid to base, or base to acid

•• Use an indicator or a pH meter to find the Use an indicator or a pH meter to find the endpoint.endpoint.

When a solution is neutral When a solution is neutral

[H[H₃₃OO⁺⁺]] = = [OH[OH^--]]

Hydronium Ion Concentration

Hydronium Ion Concentration = = Hydroxide Ion ConcentrationHydroxide Ion Concentration

When a solution is neutral When a solution is neutral

n n

n n

moles of acid

moles of acid = = moles of basemoles of base

this occurs at the

this occurs at the endpointendpointor or equivalence pointequivalence pointin a titration.in a titration.

At the

At the endpoint endpoint: :

Neutralization has occurred, and so Neutralization has occurred, and so

M M

V V

= = M M

V V

(Acid)

(Acid) (Base) (Base) Can be used to calculate the Can be used to calculate the concentration of the unknown.

concentration of the unknown.

Acid

Acid- -Base Base Titration:

Titration:

Titration Calculations Practice Titration Calculations Practice

Find the Molarity of 50.0 mL an unknown acid solution if only 75.0 mL of 0.125 M

NaOH is needed for neutralization.

At the endpoint:

At the endpoint:

n n_AA = = nn_BB

(Acid) (Acid) (Base(Base))

MM_AAVV_AA = M= M_BBVV_BB Key Idea:

Key Idea:

Titration Calculations Practice Titration Calculations Practice

If it takes 18.7 mL of a 1.0 M If it takes 18.7 mL of a 1.0 M NaOH solution to neutralize NaOH solution to neutralize 10.0 mL of HCl, what is the 10.0 mL of HCl, what is the concentration of the HCl ? concentration of the HCl ?

At the endpoint:

At the endpoint:

nn_AA = = nn_BB

(Acid) (Acid) (Base(Base))

MM_AAVV_AA = M= M_BBVV_BB Key Idea:

Key Idea:

Titration Calculations Practice Titration Calculations Practice

How much of a 0.275 M HCl How much of a 0.275 M HCl will be needed to neutralize will be needed to neutralize 25.0 mL of 0.15 M NaOH?

25.0 mL of 0.15 M NaOH?

At the endpoint:

At the endpoint:

nn_AA = = nn_BB

(Acid) (Acid) (Base(Base))

MM_AAVV_AA = M= M_BBVV_BB Key Idea:

Key Idea:

Another one Another one





.05 moles of HCl is dissolved in 500 mL of .05 moles of HCl is dissolved in 500 mL of water. If 25 mL of the acid is added to a water. If 25 mL of the acid is added to a .05 molar solution of NaOH. How many .05 molar solution of NaOH. How many mL of base will be needed to titrate the mL of base will be needed to titrate the acid to the end point?

acid to the end point?

Strong and Weak Acids Strong and Weak Acids

Strong acids are strong electrolytes Strong acids are strong electrolytes

––they completely ionize in solutionthey completely ionize in solution

There are 6 strong acids:There are 6 strong acids:



 HCl HCl hydrochloric acid hydrochloric acid



 HNOHNO₃₃ nitric acid nitric acid

HH₂₂SOSO₄₄sulfuric acid sulfuric acid



 HBrHBr hydrobromic acid hydrobromic acid

HI HI hydroiodichydroiodicacid acid



 HClOHClO₄₄perchloricperchloricacid acid



Weak acids are weak electrolytes Weak acids are weak electrolytes –

–they only partially ionize in solutionthey only partially ionize in solution Examples: any other acid

Examples: any other acid

••acetic acid vinegaracetic acid vinegar

Strong and Weak Bases



Strong bases are strong electrolytes Strong bases are strong electrolytes –

–they dissociate completely into ions in solution.they dissociate completely into ions in solution.



 LiOHLiOH lithium hydroxide lithium hydroxide



 NaOH NaOH sodium hydroxide sodium hydroxide

 KOH KOH potassium hydroxide potassium hydroxide



 RbOHRbOHrubidium hydroxide rubidium hydroxide

 CsOHCsOH cesium hydroxide cesium hydroxide



Weak bases are weak electrolytes Weak bases are weak electrolytes –

–they only partially ionize in solution they only partially ionize in solution

Ex. NH

Ex. NH

H H

O O

Strength and Concentration Strength and Concentration

The strength and concentration of an The strength and concentration of an acid or base are not the same thing!

acid or base are not the same thing!

A weak acid can A weak acid can have a dangerously have a dangerously low pH if it is highly low pH if it is highly

concentrated concentrated

A weak base can A weak base can have a dangerously have a dangerously high pH if it is highly high pH if it is highly

concentrated concentrated A strong acid can be

A strong acid can be diluted so that the pH of diluted so that the pH of the solution is not too low.

the solution is not too low.

A strong base can be A strong base can be diluted so that the pH of diluted so that the pH of the solution is not too high.

the solution is not too high.

The pH of a solution depends on its The pH of a solution depends on its

strength

strength andandits concentration.its concentration.