1 The Chemistry of Acids and Bases

2 Acids

3 Acids and Bases

4 Acid and Bases

5 Acid/Base definition Arrhenius (traditional) Acids – substances that produce H + ions (or hydronium ions H 3 O + ) in water

6 Acid/Base definition Bases – substances that produce OH - ions in water (problem with definition: some bases don’t have hydroxide ions!)

7 Some Properties of Acids Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) HC 2 H 3 O 2 ). Taste sour – vinegar is a solution of acetic acid (HC 2 H 3 O 2 ). Citrus fruits contain citric acid. Corrode metals React with certain metals to produce hydrogen gas React with carbonates and bicarbonates to produce React with carbonates and bicarbonates to produce carbon dioxide gas Electrolytes- conduct electricity React with bases to form a salt and water pH is less than 7 Turns blue litmus paper to red “Blue to Red A-CID”

8 Some Common Acids HCl hydrochloric aciddigestive juices in stomach HNO 3 nitric acidFertilizer production H 2 SO 4 sulfuric acidCar batteries H 2 CO 3 carbonic acidCarbonated beverages HC 2 H 3 O 2 acetic acidVinegar HC 2 H 3 O 2 acetic acidVinegar H 3 PO 4 Phosphoric acidFertilizer production

9 Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Are electrolytes - conduct electricity  Feel soapy, slippery. Many soaps contain bases.  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue “Basic Blue”

10 Some Common Bases NaOHsodium hydroxidelye, drain cleaner, soap production KOHpotassium hydroxideliquid soap Ba(OH) 2 barium hydroxidestabilizer for plastics Mg(OH) 2 magnesium hydroxide“MOM” Milk of magnesia Al(OH) 3 aluminum hydroxideMaalox (antacid) and deodorant Al(OH) 3 aluminum hydroxideMaalox (antacid) and deodorant

11 The pH scale is a way of expressing the strength of acids and bases. Over 7 = base 7 = neutral Under 7 = acid

12 pH of Common Substances The “bar” is colored red at one end and blue at the other. These are the colors of litmus paper, commonly used in the laboratory to decide if a solution is acidic (litmus is red) or basic (litmus is blue).

13 pH indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Once the drops are added, the sample is ruined Some dyes are natural, like radish skin or red cabbage

14 pH testing There are several ways to test pHThere are several ways to test pH –Blue litmus paper (red = acid) –Red litmus paper (blue = basic) –pH paper (multi-colored) –Universal indicator (multi-colored) –Indicators like phenolphthalein (colorless = acid, pink = base) –Natural indicators like red cabbage, radishes

15 Paper testing Paper tests like litmus paper and pH paperPaper tests like litmus paper and pH paper –Put a stirring rod into the solution and stir. –Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper –Read and record the color change. Note what the color indicates. –You should only use a small portion of the paper. You can use one piece of paper for several tests.

16 Neutralization A reaction between an acid and a baseA reaction between an acid and a base An acid-base mixture is not as acidic or basic as the individual starting solutions were.An acid-base mixture is not as acidic or basic as the individual starting solutions were.

17 Neutralization A neutralization reaction produces water and a salt.A neutralization reaction produces water and a salt. A salt is made from the positive ion of a base and the negative ion of an acid.A salt is made from the positive ion of a base and the negative ion of an acid. HCl + NaOH  H 2 O + NaCl * *Is this reaction balanced? yes *What type of reaction is this? double replacement +-

18 Neutralization What salt would form from a reaction between hydrochloric acid, HCl, and calcium hydroxide, Ca(OH) 2 ?What salt would form from a reaction between hydrochloric acid, HCl, and calcium hydroxide, Ca(OH) 2 ? Finish the equation! HCl + Ca(OH) 2 

19 Neutralization Finish the equation! HCl + Ca(OH) 2  Steps to solve: 1.Write down the ions and charges for each element in both compounds. H + Ca 2+ H + Ca 2+ Cl - OH - Cl - OH - The product will be a salt and water.

20 Neutralization Finish the equation! HCl + Ca(OH) 2  2.“Criss cross” the ions to find the products. H + Ca 2+ Cl - OH - 3.Complete the equation. H + + OH -  H 2 O Ca 2+ + Cl -  CaCl 2 HCl + Ca(OH) 2  H 2 O + CaCl 2 The salt formed is calcium chloride!

21 Acid Rain Normal rainfall is slightly acidic with a pH of approximately 5.5.Normal rainfall is slightly acidic with a pH of approximately 5.5. Acidity comes from carbon dioxide in the air.Acidity comes from carbon dioxide in the air. Carbon dioxide dissolves in rainwater, producing carbonic acid, a weak acid.Carbon dioxide dissolves in rainwater, producing carbonic acid, a weak acid. H 2 O + CO 2  H 2 CO 3 H 2 O + CO 2  H 2 CO 3

22 Acid Rain Acid rain is more acidic than normal rainwater.Acid rain is more acidic than normal rainwater. It has a pH as low as 3.5 to 3.0.It has a pH as low as 3.5 to 3.0. The extra acidity comes from nitrogen oxides and sulfur oxides—gases released into the air as pollutants from industry and motor vehicles.The extra acidity comes from nitrogen oxides and sulfur oxides—gases released into the air as pollutants from industry and motor vehicles. –Form nitric acid and sulfuric acid –Acid rain can damage statues and buildings, destroy forests, kill fish in lakes

23 Acid Rain Effects

24 Acidity of precipitation measured by the National Atmospheric Deposition Program. Notice that precipitation is most acidic downwind of the large concentration of power plants in the Ohio Valley.

25 Acid Rain and Lakes The damaging effects of acid rain do not appear in bodies of fresh water lined with calcium carbonate, which acts to neutralize any acidity. Lakes and rivers lined with inert materials are not so protected.