Acids and Bases

Take notes on your own paper today… Write down things that are in yellow You’ll need this information to answer the lab questions

Svante Arrhenius He was a Swedish chemist (1859-1927), and a Nobel prize winner in chemistry (1903) one of the first chemists to explain the chemical theory of the behavior of acids and bases Dr. Hubert Alyea (professor emeritus at Princeton University) was the last graduate student of Arrhenius.

Hubert N. Alyea (1903-1996)

1. Arrhenius Definition - 1887 Acids produce hydrogen ions (H1+) in aqueous solution (HCl → H1+ + Cl1-) Bases produce hydroxide ions (OH1-) when dissolved in water. (NaOH → Na1+ + OH1-)

Svante Arrhenius (1859-1927)

2. Brønsted-Lowry – 1923 A broader definition than Arrhenius Acid is hydrogen-ion donor (H+ or proton); base is hydrogen-ion acceptor. Acids and bases always come in pairs. HCl is an acid. When it dissolves in water, it gives it’s proton to water. HCl(g) + H2O(l) ↔ H3O+(aq) + Cl-(aq) Water is a base; makes hydronium ion.

Johannes Brønsted Thomas Lowry (1879-1947) (1874-1936) Denmark England

Properties of Acids Acids taste sour Acids have a pH lower than 7 Acids effect indicators Blue litmus turns red Universal indicator turns red Acids are proton (hydrogen ion, H+) donors Acids react with active metals, produce H2 Acids react with carbonates Acids neutralize bases

Acids Effect Indicators Blue litmus paper turns red in contact with an acid.

Acids Have a pH less than 7

Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas. Mg + 2HCl  MgCl2 + H2(g)

Acids Neutralize Bases HCl + NaOH  NaCl + H2O Neutralization reactions ALWAYS produce a salt and water.

Sulfuric Acid Used in the production of paper Highest volume production of any chemical in the U.S. Used in the production of paper Used in production of fertilizers Used in petroleum refining

Nitric Acid Used in the production of fertilizers Used in the production of explosives Nitric acid is a volatile acid – its reactive components evaporate easily Stains proteins (including skin!)

Hydrochloric Acid Used in the pickling of steel Used to purify magnesium from sea water Part of gastric juice, it aids in the digestion of protein Sold commercially as “Muriatic acid”

Phosphoric Acid A flavoring agent in sodas Used in the manufacture of detergents Used in the manufacture of fertilizers Not a common laboratory reagent

Acetic Acid Used in the manufacture of plastics Used in making pharmaceuticals Acetic acid is the acid present in vinegar

Organic Acids Organic acids all contain the “carboxyl” group, sometimes several of them. The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.

Examples of Organic Acids Citric acid in citrus fruit Malic acid in sour apples Deoxyribonucleic acid, DNA Amino acids, the building blocks of protein Lactic acid in sour milk and sore muscles Butyric acid in rancid butter

Acids are Proton Donors Monoprotic acids Diprotic acids Triprotic acids HCl H2SO4 H3PO4 HC2H3O2 H2CO3 HNO3

Ionization of HCl and formation of hydronium ion, H3O+ H2O + HCl  H3O+ + Cl- Proton acceptor Proton donor

Strong Acids vs. Weak Acids Strong acids are assumed to be 100% ionized in solution (good proton donors). HCl H2SO4 HNO3 Weak acids are usually less than 5% ionized in solution (poor proton donors). H3PO4 HC2H3O2 Organic acids

Effects of acid on the Environment Rainwater is naturally acidic WHY? When CO2 (gas) + H2O H2CO3 (aqueous) react they form Carbonic acid Carbon dioxide (from the air) dissolves in rainwater, producing carbonic acid, a weak acid The normal pH of rainwater is about 5.6

Effects of acid on the Environment Acid rain is rain with a pH less than 5. Forms when air-polluting gases dissolve in Rainwater Sulfur dioxide (SO2) Further lowers the pH of rain.

Effects of acid on the Environment Environmental Impact of Acid Rain Dependent on local geology Hill Country soil is rich in limestone (CaCO3), which is basic Limestone neutralizes the effect of acid rain on lakes

Damages Caused by Acid Rain 1) Damage to aquatic life In some sensitive lakes and streams, acidification has completely eradicated fish species, such as the brook trout, leaving these bodies of water barren. Hundreds of the lakes in the Adirondacks have acidity levels unsuitable for the survival of fish

Damages Caused by Acid Rain (Cont.) 2.) Damage to vegetation

Damages Caused by Acid Rain (Cont Damages Caused by Acid Rain (Cont.) 3) Damage to outdoor artwork (monuments & statues)

Properties of Bases Bases taste bitter Bases have a pH greater than 7 Bases effect indicators Red litmus turns blue Universal indicator turns blue Phenolphthalein turns purple Bases are proton (H+) acceptors and usually have hydroxide ions- OH- Solutions of bases feel slippery Bases neutralize acids

Examples of Bases Sodium hydroxide (lye), NaOH Potassium hydroxide, KOH Magnesium hydroxide, Mg(OH)2 Calcium hydroxide (lime), Ca(OH)2

Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns purple in a base.

Bases have a pH greater than 7

Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O

Products of Neutralization HCl + NaOH  NaCl + H2O H2SO4 + Ca(OH)2  CaSO4 + 2 H2O HNO3 + KOH  KNO3 + H2O The products of neutralization are always a ______ and _______. salt water