Acids and bases: Properties and definition

We encounter acids in our daily lives acetic acid (CH 3 CO 2 H) citric acid (C 6 H 8 O 7 ) hydrochloric acid (HCl)

We encounter bases in our daily lives ammonia (NH 3 ) sodium hydroxide (NaOH)

An acid is a substance that produces H + when dissolved in water HX H + (aq) + X - (aq) H2OH2O HCl H + (aq) + Cl - (aq) H2OH2O Aqueous (or aq) is a solution wherein water is the solvent Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill. CH 3 CO 2 H H + (aq) + CH 3 CO 2 - (aq) H2OH2O The double-headed arrow signifies that the reaction goes forward and reverse

A base is a substance that produces OH - when dissolved in water MOH M + (aq) + OH - (aq) H2OH2O NaOH Na + (aq) + OH - (aq) H2OH2O Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd. Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill. NH 3 NH 4 + (aq) + OH - (aq) H2OH2O The double-headed arrow signifies that the reaction goes forward and reverse

Acids and bases have the following properties Acids taste sour aqueous acid conducts electricity Bases taste bitter feel slippery aqueous base conducts electricity Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill.

Ions cause aqueous solutions to be good conductors to light the bulb, electric current must flow between the two wires ions carry electrical charge from one wire to another, thereby completing the circuit copper wire

Acid-base reaction (aka neutralization reaction)

An acid-base reaction is a reaction between an acid and a base to form salt and water acid + base  salt + water salt is an ionic compound made of a cation other than H + and an anion other than OH - or O 2- HCl + NaOH  NaCl + H 2 O CH 3 CO 2 H + KOH  KCH 3 CO 2 + H 2 O Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill.

When vinegar reacts with baking soda, water and carbon dioxide are produced CH 3 CO 2 H + NaHCO 3  NaCH 3 CO 2 + H 2 CO 3 H 2 CO 3  H 2 O + CO 2

Acid-base indicators

An indicator is a substance that is added to a solution. It turns one color in an acidic medium and turns another color in a basic medium litmus paper phenolphthalein Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd.

Litmus paper contains various organic compounds. It changes color depending on the acidity/basicity of a solution red to blue: base blue to red: acid

Phenolphthalein is colorless in acidic and neutral solutions but reddish pink in basic solutions Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. Skoog, D., D. West, and F.J. Holler Fundamentals of Analytical Chemistry 7 th ed. USA: Saunders College Publishing. colorlessreddish pink

pH

pH is a logarithmic scale that indicates the amount of H + in solution pH = - log [H + ] where [H + ] = concentration of H + in units of molarity = moles H + / L of solution

An HCl solution has [H + ] = 1.00 x M. Calculate for the pH of the solution pH = - log [H + ] pH = - log [1.00 x ] = 6.00

pH values indicate if a solution is acidic, neutral, or basic If pH < 7.00, solution is acidic If pH = 7.00, solution is neutral If pH > 7.00, solution is basic

Schedule Feb 29 –deadline for the submission of outline Mar 7 (4:30-6:00 pm) – LT # 3 Mar 9-16 –group reports Mar 21 (11:30-1:30, C-109) –finals

pH of some familiar aqueous solutions Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill.

Acid rain

Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill. The effect of industrial society on the environment is especially apparent in the problem of acid rain major substances involved in acid rain

SO 2 is converted to H 2 SO 4 SO 2 SO 3 Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill. oxidation SO 3 + H 2 O  H 2 SO 4 from power plant emissions

SO 2 is converted to H 2 SO 4 SO 2 + H 2 O  H 2 SO 3 from coal H 2 SO 3 + H 2 O 2  H 2 SO 4 + H 2 O air pollutant Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill.

Nitrogen oxides (NO x ) are converted to HNO 3 N 2 + O 2  NO x NO x  N 2 O 5 at night, N 2 O 5 + H 2 O  HNO 3 Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill.

NO is converted to NO 2 and HNO 3 NO  NO 2 + HNO 3 Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill. from combustion in car engines and electric power plants

The pH of rain and snow has adversely declined in many parts of the world Much of the United States –as early as 1984, average rainfall pH = 4.2 Sweden –rain with pH = 2.7 (about the same as vinegar) has been observed West Virginia –rain with pH = 1.8 (between lemon juice and stomach acid) has been observed Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill.

Acid rain is harmful to marble buildings and sculptures Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill.

Acid rain is harmful to the ecosystem

Honey, I told you not to leave your bike out in the rain!

Antacids

It is natural to have HCl in the stomach, but the problem occurs when the amount of HCl is too high Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. CO 2 + H 2 O H 2 CO 3 H 2 CO 3 H + + HCO 3 - in the blood plasma, by-product of metabolism

To temporarily reduce the amount of HCl in the stomach, an antacid may be taken. The HCl and the antacid undergo an acid-base reaction Kremil-S and Maalox contain Al(OH) 3 and Mg(OH) 2 3HCl +Al(OH) 3  AlCl 3 + 3H 2 O 2HCl +Mg(OH) 2  MgCl 2 + 2H 2 O Chang, R Chemistry 7th ed. Singapore: McGraw-Hill. Silberberg, M Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill.

Acid inhibitors prevent the production of gastric acids by acting on acid-producing cells in the lining of the stomach