The Chemistry The Chemistry of Acids and of Acids and BasesBases

The Chemistry The Chemistry of Acids and of Acids and BasesBases

Some Properties of Acids

Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule)

Taste sour

Corrode metals

React with bases to form a salt and water

pH is less than 7

Some Properties of Bases

Produce OHProduce OH-- ions in water ions in water

Taste bitter, chalkyTaste bitter, chalky

Feel soapy, slipperyFeel soapy, slippery

React with acids to form salts React with acids to form salts and waterand water

pH greater than 7pH greater than 7

Acid is a substance that produces H+ (H3O+) in water

Base is a substance that produces OH- in water

Calculating the pH

pH = - log [H+](the [ ] mean Molarity)

Example: If [H+] = 1 X 10-10

pH = - log 1 X 10-10

pH = - (- 10) = 10

Example: If [H+] = 1.8 X 10-5

pH = - log 1.8 X 10-5

pH = - (- 4.74) = 4.74

Try These!Try These!Find the pH of these:Find the pH of these:

1)1) A 0.15 M solution of Hydrochloric acidA 0.15 M solution of Hydrochloric acid

2) A 3.00 X 102) A 3.00 X 10-7-7 M solution of Nitric acid M solution of Nitric acid

pOH• Since acids and bases are opposites, Since acids and bases are opposites,

pH and pOH are opposites!pH and pOH are opposites!• pOH does not really exist, but it is pOH does not really exist, but it is

useful for changing bases to pH.useful for changing bases to pH.

• pOH looks at the perspective of a basepOH looks at the perspective of a basepOH = - log [OHpOH = - log [OH--]]

• Since pH and pOH are on opposite Since pH and pOH are on opposite ends,ends, pH + pOH = 14pH + pOH = 14

pHpH [H+][H+] [OH-][OH-] pOHpOH

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

The strength of an acid (or base) is determined by the amount of IONIZATION, that is, how many acid (or base) molecules break up into ions.

The strength of an acid (or base) is determined by the amount of IONIZATION, that is, how many acid (or base) molecules break up into ions.

STRONG ACIDSTRONG ACID

• Weak acidsWeak acids are much less than 100% ionized in are much less than 100% ionized in water… so many molecules of a weak acid stay water… so many molecules of a weak acid stay together in water!together in water!

One of the best known is acetic acid = CHOne of the best known is acetic acid = CH33COOHCOOH

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

• Strong Base:Strong Base: 100% dissociated in water.100% dissociated in water.

NaOH (aq) ---> NaNaOH (aq) ---> Na+ + (aq) + OH(aq) + OH- - (aq)(aq)

• Weak base:Weak base: less than 100% ionized in less than 100% ionized in water… so again, many molecules of a water… so again, many molecules of a weak base stay together in water!weak base stay together in water!

Strong and Weak Strong and Weak Acids/BasesAcids/Bases