Acids and Bases

Strong Acid (SA)•an acid that dissociates completely into

ions in water

Ex. All molecules of HCl(aq) dissociate into

H+ and Cl- ions▫H+ ions that are formed bond with H2O to

form H3O+

HCl(aq) + H2O(l) H3O+(aq) + Cl-

(aq)

Dissociation (Strong Acid)100% of hydrogen chloride molecules

dissociate

Strong Acid Examples

HBrHIHNO3

H2SO4

HClO4

Weak Acid (WA)

• an acid that dissociates very slightly into ions in waterEx. not all molecules of CH3COOH(aq)

break apart, some remain intact• only about 1% of acetic acid molecules

dissociate

Dissociation (Weak Acid)1% of acetic acid molecules dissociate. In solution there are mostly acetic acid molecules and only some ions.

Concentration

•the concentration of H3O+(aq) ions,

[H3O+], in a dilute solution of a SA is equal to the concentration of the acid, [acid]

[H3O+] = [strong acid]

•Ex. In a sample of 1.0 mol/L HCl(aq)

[H3O+] = 1.0 mol/L square bracketMolar Concentration

Recall: C = n V

Concentration

•the concentration of H3O+(aq) ions,

[H3O+], in a dilute solution of a WA is much less than the concentration of the acid, [acid]

• Ex. In a sample of 1.0 mol/L CH3COOH

(aq)

[H3O+] <<< 1.0 mol/L

• That is, [H3O+] < [weak acid]

Strong Base (SB)

• a base that dissociates completely into ions in waterEx. all molecules of NaOH(aq) dissociate

into Na+ and OH- ions• other SB’s are…

KOHCa(OH)2

Ba(OH)2

Weak Base (WB)

•most bases are weak•WB dissociates very slightly into ions

in water▫Ex. Ammonia [OH1-] < [weak base]

Concentration

•the concentration of OH1-(aq) ions,

[OH1-], in a dilute solution of a SB is equal to the conc. of the base, [base]

[OH1-] = [strong base]

Ex. In a sample of 1.0 mol/L NaOH(aq)

[OH1-] = 1.0 mol/L

pH

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pH [H3O+ ] [OH- ] pOH

Measuring Strength – pH Scale•In pure water,

[H3O+] = [OH-] = 1.0 x 10-7 mol/L

•In acidic solution, [H3O+] > [OH-]

•In basic solution, [H3O+] < [OH-]

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pH and acidity

The pH values of several common substances are shown at the right.

Many common foods are weak acids

Some medicines and many household cleaners are bases.

Indicators

• An acid-base indicator is a substance that changes colour in acid and base solutions. It is used to determine if neutralization is complete.

• ex. litmusphenolphthalein (phth)bromothymol blue (BTB)universal indicator

pH Scale Review• Now that we know when an acid or base is

dissolved in water it will produce either:▫ OH-▫ H+

• pH measures the concentration (how many) of H+ in the solution

• When pH is 7 that means the concentration of OH- is equal to H+

• When pH is less than 7 we have a higher concentration of H+

• When pH is bigger that 7 we have a higher concentration of OH-

Acid-Base Reactions

Neutralization

•Adding a base to an acid neutralizes the acid’s acidic properties.

•This is called a neutralization reaction.▫Ex. for an upset stomach, use an ANTACID

Neutralization

•In general:

ACID + BASE SALT + WATER

H2SO4(aq) + Ca(OH)2(aq) CaSO4(aq) + 2H2O(l)

Example1. In an experiment, 15.85 mL of HCl(aq)

completely neutralizes 25.00 mL of 0.125 mol/L KOH(aq). Calculate the concentration of this acid.

Example 22. What volume of 0.185 mol/L H2SO4(aq) will

react completely with 25.00 mL of 0.225 mol/L KOH(aq)?

Learning Check3. What mass of aluminum hydroxide will react

completely with 27.50 mL of 0.255 mol/L H2SO4(aq)?

Learning Check 2

4. What is the molar concentration of phosphoric acid if 17.50 mL of this acid reacted with 3.22 g of magnesium hydroxide?

Titration• lab procedure involving neutralization, used to

determine an unknown concentration• progressive addition of a solution (called

titrant) from a graduated tube (called burette) to a known volume or mass of a second solution, until the endpoint▫endpoint is indicated by a colour change of an

added indicator• at equivalence point, nH+ = nOH-

▫given the concentration of one sol’n, you can calculate the concentration of the other sol’n

Titration

•Read p468 - 469 to review procedure

Homework

•pg 457 Q 1, 4•pg 462 Q 8, 9•pg 466 Q 1, 3, 4, 10•pg 467 Q 13, 16