The Chemistry of Acids and Bases

Some Properties of Acids þ Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) þ Taste sour þ Corrode metals þ React with bases to form a salt and water þ pH is less than 7

Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7

Acid is a substance that produces H + (H 3 O + ) 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 pH = - log 1 X pH = - (- 10) = 10 Example: If [H + ] = 1.8 X pH = - log 1.8 X pH = - (- 4.74) = 4.74

Try These! Find the pH of these: 1)A 0.15 M solution of Hydrochloric acid 2) A 3.00 X M solution of Nitric acid

pOH Since acids and bases are opposites, pH and pOH are opposites!Since acids and bases are opposites, pH and pOH are opposites! pOH does not really exist, but it is useful for changing bases to pH.pOH does not really exist, but it is useful for changing bases to pH. pOH looks at the perspective of a basepOH looks at the perspective of a base pOH = - log [OH - ] Since pH and pOH are on opposite ends,pH + pOH = 14Since pH and pOH are on opposite ends,pH + pOH = 14

pH [H + ] [OH - ] pOH

Strong and Weak Acids/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. STRONG ACID

Weak acids are much less than 100% ionized in water… so many molecules of a weak acid stay together in water!Weak acids are much less than 100% ionized in water… so many molecules of a weak acid stay together in water! One of the best known is acetic acid = CH 3 COOH One of the best known is acetic acid = CH 3 COOH Strong and Weak Acids/Bases

Strong Base: 100% dissociated in water.Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) NaOH (aq) ---> Na + (aq) + OH - (aq) Weak base: less than 100% ionized in water… so again, many molecules of a weak base stay together in water!Weak base: less than 100% ionized in water… so again, many molecules of a weak base stay together in water! Strong and Weak Acids/Bases