Acids, Bases, and pH

Properties of acids 1. Sour taste

2. Contain hydrogen, react with active metals to give off H 2 gas

3. Change the color of indicators

4. React with bases to produce salts and water e.g. 2NaOH + H 2 SO 4 → 2H 2 O + Na 2 SO 4

5. Acids are electrolytes

Traditional definition of an acid • A cmpd. That contains hydrogen and ionizes in aqueous soln. to form hydrogen ions (H + )

Common acids • • • • • HCl – hydrochloric acid H 2 SO 4 – sulfuric acid HC 2 H 3 O 2 – acetic acid HNO 3 H 3 PO 4 – nitric acid – phosphoric acid

Sulfuric acid • • • #1 industrial chemical Fertilizers, petroleum refining, …… Used as a measure of a country’s economy

Acetic acid • Dilute acetic acid is vinegar

Acid Precipitation • Combustion of fossil fuels – Is the main cause of acid precipitation

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Bases

Properties of bases 1. Bitter taste

2. Feel slippery to the skin 3. Change color of indicators

4. React with acids to produce water and salts e.g.

2NaOH + H 2 SO 4 → 2H 2 O + Na 2 SO 4 5. Bases are electrolytes

Traditional definition of a base • OH producer

Neutralization reactions • Reaction of hydronium ions (H 3 O + ) and hydroxide (OH ) ions to form water H 3 O + + OH  2H 2 O HCl + NaOH  (NaCl is a salt) H 2 O + NaCl

Common bases

Sodium hydroxide • ( NaOH ), also known as lye or caustic soda, is a a strong caustic metallic chemical base base . It is widely used in many industries, mostly as in the manufacture of pulp soaps production in 1998 was around 45 million tons . and paper , textiles , drinking water , and detergents . Worldwide

pH scale

pH • • - log [H + ] e.g. if [H + ] = 1 x 10 -8 M pH = 8

If [H + ] = 3.4 x 10 -5 find pH = -[(log 3.4 + log 10 -5 )] = -[(0.53) + (-5)] = -(0.53 – 5) = 4.47

If the pH is 2 what is the [H + ] pH = -log [H + ] log [H + ] = -pH [H + ] = antilog (-pH) = antilog (-2) = 1 x 10 -2 M

If the pH is 6.4 what is [H + ] [H + ] = antilog (-pH) = antilog (-6.4) = 4.0 x 10 -7 M

If the pH is 5.4 what is [H + ] [H+] = antilog (-pH) = antilog (-5.4) = 4.0 x 10 -6 M

[H + ] [OH ] = 1 x 10 -14 • Therefore if [OH ] = 1 x 10 -10 pH = 4 • if [OH ] = 1 x 10 -7 pH = 7

Diprotic acid • • Can donate (2) protons (H + ) per molecule e.g. H 2 SO 4

Triprotic • • Donates (3) protons e.g. H 3 PO 4

Normality ( N ) = (molarity) x (whole # factor) # equivalents solute / L of solution

What is the normality of a soln w/ 1 mol H 2 SO 4 dissolved in 1 L of soln?

2 1 equivalents mol x 1 mol H 2 SO 4 = 2 equivalents H 2 SO 4 1 L 1 L = 2 N H 2 SO 4

Titration • Controlled addition & measurement of amt. of soln. of a known conc. That is required to react completely with a measured amt. of soln. of unknown conc.

Graph of titration results

Saponification • hydrolysis of an ester conditions to form an under basic of a carboxylic acid a metallic alkali ( . Saponification is commonly used to refer to the reaction of base ) with a fat or oil to form soap . alcohol and the salt