1

2 Acid and Bases

3

4

5 Some Household Acids and Bases

6 Acids Have a sour taste. Vinegar is a solution of acetic acid. Citrus fruits contain citric acid. Will react with certain metals to produce hydrogen gas. Will react with carbonates and bicarbonates to produce carbon dioxide gas. Have a bitter taste. Feel slippery. Many soaps contain bases. Bases

7 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 Electrolytes þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red (red = acid)

8 Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue “Base = Blue”

9 Some Common Bases NaOHsodium hydroxidelye 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) Al(OH) 3 aluminum hydroxideMaalox (antacid)

10 Reactions of acids and bases HNO 3 + KOH -> KNO 3 + H 2 O A reaction between an acid and a base is a type of double replacement reaction called neutralization. In a neutralization reaction, water and a salt are produced.

11 Some Properties of Salts A salt is the combination of an anion (- ion) and a cation (+ ion). Salts are products of the reaction between acids and bases. Solid salts are usually crystalline. If a salt dissolves in water, it usually breaks up into the ions that make up the salt.

12 Strong Acids and Bases Strong acids are those that break apart (dissociate) completely in water. What does the diagram on the right show about how strong acids break apart?

13 7 Strong Acids HNO 3 - nitric acid HCl - hydrochloric acid HBr - hydrobromic acid HI - hydroiodic acid H 2 SO 4 - sulfuric acid HClO 4 - perchloric acid HClO 3 - chloric acid Strong acids are assumed to ionize completely (100%) in water. They exist as H 3 O + ions in water. This is known as “the leveling effect”.

14 Strong Bases LiOH - lithium hydroxide NaOH - sodium hydroxide KOH - potassium hydroxide RbOH - rubidium hydroxide CsOH - cesium hydroxide Ba(OH) 2 - barium hydroxide Sr(OH) 2 - strontium hydroxide Ca(OH) 2 - calcium hydroxide GROUP 1 hydroxides Some GROUP 2 hydroxides In most cases, strong bases will also ionize completely in water.

15 Weak Acids and Bases Some acids and bases ionize only slightly in water. These are considered weak. The most important weak base is ammonia.

16 Balance of ions in acidic solutions Acidic Neutral Solution

17 ANIMATION LINKS Acid ionization equilibrium demo

18 The pH scale is a way of expressing the strength of acids and bases instead of using very small numbers. It ranges from Under 7 = acid 7 = neutral Over 7 = base

19 pH of Common Substances

20 pH testing There are several ways to test pHThere are several ways to test pH –Blue litmus paper (red = acid) –Red litmus paper (blue = base) –pH paper (multi-colored) –pH meter (7 is neutral, 7 base) –Universal indicator (multi-colored) –Indicators like phenolphthalein –Natural indicators like red cabbage, radishes

21 Indicators

22 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.

23 pH and Flowers For most big leaf hydrangeas, blue flowers will be produced in acidic soil (pH 5.5 and lower), whereas neutral to alkaline soils (pH 6.5 and higher) will usually produce pink flowers. Between pH 5.5 and pH 6.5, the flowers will be purple (see image at right) or a mixture of blue and pink flowers will be found on the same plant.

24 Conjugate acid-base pairs Neutralization reaction example: HCl + HOH ↔ H 3 O + + Cl¯ Notice that each pair (HCl and Cl¯ as well as HOH and H 3 O + differ by one hydrogen ion (H + ). These pairs are called conjugate pairs. Example: HNO 3 + HOH ↔ H 3 O + + NO 3 ¯ What is the conjugate base to the acid HNO 3 ? What is the conjugate acid to the base HOH? What are the pairs?

25 WHAT IS A BUFFER? A buffer solution is one which resists changes in pH when small quantities of an acid or a base are added to it. How do buffer solutions work? A buffer solution has to contain things which will remove any hydrogen ions or hydroxide ions that you might add to it - otherwise the pH will change. buffer demo

26 Definition of Acid Rain Precipitation that has a pH less than that of natural rainwater (which is about 5.6 due to dissolved carbon dioxide). It is formed when sulfur dioxides and nitrogen oxides (gases or fine particles in the atmosphere) combine with water vapor and precipitate as sulfuric acid or nitric acid in rain, snow, or fog.

27 What Causes Acid Rain? Natural Sources -Emissions from volcanoes and from biological processes that occur on the land, in wetlands, and in the oceans contribute acid-producing gases to the atmosphere -Effects of acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe The principal cause of acid rain is from human sources -Industrial factories, power-generating plants and vehicles -Sulfur dioxide and oxides of nitrogen are released during the fuel burning process (i.e. combustion)

28 How Does Acid Rain Form?

29 Formation of Acid Rain When water vapor condenses, or as the rain falls, the gases and particles dissolve in the water to form sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ). While the air is cleansed of the pollutants in this way, it also causes precipitation to become acidic, forming acid rain.

30 Formation of Acid Rain

31 What Areas Are Most Affected? Canada -Water and soil systems lack natural alkalinity such as lime base and cannot neutralize acid Industrial acid rain is a substantial problem in China, Eastern Europe and Russia and areas down-wind from them. Acid rain from power plants in the Midwest United States has also harmed the forests of upstate New York and New England. NOTE: This shows that the effects of acid rain can spread over a large area, far from the source of the pollution

32

33 Effects of Acid Rain Harmful to aquatic life –Increased acidity stops eggs of certain organisms (e.g. fish) from hatching –Changes population ratios and affects the tissues of sensitive organisms Harmful to vegetation - Increased acidity in soil –Removes nutrients from soil, slowing plant growth –Dissolves toxins from soil, poisoning plants –Creates brown spots in leaves of trees, impeding photosynthesis –Allows pests to infect vegetation through broken leaves

34 Effects of Acid Rain Harmful to buildings -Accelerates weathering in metal and stone structures, and roads -Ex: Parthenon in Athens, Greece; Taj Mahal in Agra, India Harmful to human health –Respiratory problems, asthma, dry coughs, headaches and throat irritations –Leeching of toxins from the soil by acid rain can be absorbed by plants and animals. When consumed, these toxins affect humans.

35

36 Effects of Acid Rain

37 What can we do? Reduce amount of sulfur dioxide and oxides of nitrogen released into the atmosphere –Use less energy (less fuel burned) –Use cleaner fuels that contain less sulfur –Remove oxides of sulfur and oxides of nitrogen before releasing –Use other sources of energy such as solar, geothermal, nuclear, wind, etc… (more expensive) –Liming: powdered limestone or limewater added to water and soil to neutralize acid (expensive)

38 CAPT Activity: Brownfields Link to North Haven Pharmacia and Upjohn LLC site: d.phphttp:// d.php