Ions Charged Particles in Solution Chapter 6 You

Ions: Charged Particles in Solution Chapter 6 You have probably heard the terms sour stomach, bitter herbs, buffered aspirin, heartburn and acid rain. What do these terms describe? How are they related? We will look at charged particles in solution. You will also be defining the terms, acids, bases, and salts.

I. Defining Acids and Bases A. The ionization of water: pure water is not just a group of H 2 O molecules. At any given time a small number of molecules in a volume of water are separating into ions and then recombining. This process of forming ions is called ionization.

• When water ionizes, both hydrogen and hydroxide ions are produced

• Acids are substances that create a surplus of hydrogen ions or hydronium ions. Acids have a positive charge – H+

• Bases are substances that produce a surplus of hydroxide ions. Bases have a negative charge. Bases are also called alkalis – OH -

• If acids and bases combine to form a compound with ionic bonds, that compound is called a salt.

• A substance is neutral when it has an equal number of positive and negative charges. Pure water is neutral because it always has an equal number of hydronium and hydroxide ions.

B. Identifying Acids and Bases 1. Sensory Evaluation of Acids and Bases: a simple way to identify many acids and bases is by sensory evaluation such as taste testing.

• Acids taste sour, lemons, grapefruit, cranberries, vinegar, and yogurt contain acids that are safe. Soda and tea are acidic. So is CO 2

• Bases are bitter, milk of magnesia, and baking soda are examples of bases that are safe to taste. • You can also touch some acids and bases. If safe, bases feel slippery. Soaps and cleaners are bases.

2. Organic Dyes • Are naturally occurring color pigments that change color when exposed to acids or bases. The most widely used organic dye in science classes is litmus

• Litumus is extracted from a plant and added to paper strips. • These strips when dipped in acids turn red and when dipped in bases turn blue. • p. Hydrion paper is another indicator used in labs. It turns shades of yellow to orange red in acids and yellow green to blue green in bases.

• Acids and bases affect the colors of fruits and vegetables that contain organic dyes. They include plums, blueberries, cherries, red onions, and red cabbage. • Cooking red cabbage in an acidic mixture will help the cabbage retain its color. • Green vegetables will be brighter green if you add baking soda while cooking. It is not recommended because baking soda is a base and it will neutralize the vitamin C

II. Measuring Acids and Bases • p. H scale was developed to express the degree of concentration of hydrogen or hydronium ions present in a solution.

• The larger the number of hydronium ions in a solution, the more concentrated the acid will be. • “p” stands for “power of” and the “H” stands for “hydronium ions”

• p. H 1. 0 would be hydrochloric acid in the human stomach. Coffee is 5. 0, water is 7. 0, neutral. A base has a p. H of 7. 1 to 14. 0 • The greater the hydrogen or hydronium ion concentration is, the more concentrated the acid and the lower the p. H will be. The greater the hydroxide ion concentration is, the more concentrated the base and the higher the p. H will be.

A. Measuring p. H: there are two methods. 1. Most economical is using organic dyes called indicators. It demonstrates through color change the degree of acidity of a solution. They are not very accurate.

2. Titration: is the other method of measuring. It is the process of adding a base with a known p. H to an acid. It is also the process of adding an acid with a known p. H to a base. An indicator is added to the unknown. Using a burette, the base or acid whose p. H is known is dispensed into the unknown a drop at a time. Scientists look for a color change.

3. The point at which there an equal number of acid and base molecules is called the endpoint, also called the equivalence point. This is where neutralization has occurred.

4. Neutralization is the point at which all ions in a solution have combined chemically

B. Measuring Concentrations of Acids and Bases • Titration can work only if you have a known solution. You must know the volume and concentration. • Concentration: the measure of parts of one substance to the known volume of another.

III. Application of p. H A. p. H and digestion 1. Digestion first takes place in the mouth with saliva, which has a p. H of 6. 5.

2. To digest proteins, the stomach produces on of nature’s strongest acids – hydrochloric acid. p. H of stomach is 1. 5 -1. 7 3. Digestion continues in the small intestine where the p. H is around 7. 0 by the addition of pancreatic juice. Bile is also added.

4. The body maintains the p. H of the bloodstream at about 7. 4. 5. People who believe they have excess stomach acid may really have stomachs that are too full. 6. A full stomach can stretch the valve to the esophagus which causes stomach acid to splash up into the esophagus.

7. Bulimia: an eating disorder that involves induced vomiting. The acids from the stomach eat away to the tooth enamel and the skin of the mouth.

B. The Role of Buffers: a buffer is a compound that helps stabilize p. H by absorbing excess acids or bases in a solution. 1. It is made by combining a weak acid or base and one of its salts.

2. The stability of the blood p. H is so important the body has three buffering systems to maintain the balance. 3. Lactic acid is a byproduct of energy production; ammonia is a result of protein digestion and the third buffering agent is proteins found in blood plasma.

4. Buffers are also used to coat some aspirin tablets to make them easier to digest without damaging the digestive system.

C. Food Preservation Food spoilage is caused by microorganisms growing in and feeding on food. 1. Most bacteria thrive in an environment that has a p. H of 5. 0 to 7. 0. Preserving food and keeping it safe depend on understanding p. H.

• Botulism: deadliest food borne illness. Caused by toxin produced by the bacteria Clostridium botulinum. It is commonly found in many foods with a p. H above 4. 6. These are low acid foods. If canned, these foods need to be at a very high temperature.

• Many low acid foods can be preserved by the pickling process. This changes the texture, flavor and p. H. • Pickling involves soaking or heating foods in vinegar solution. The vinegar helps lower the p. H so harmful bacteria can’t grow. • Buttermilk and yogurt have a naturally low p. H. If stored properly these and other low p. H foods will stay fresh longer.

• Molds will grow in a wide range of p. H from 28. 5. Mold and p. H monitoring are a part of the processing of tea, coffee, chocolate, cheese and shelf-stable juices. • Salts are a by-product of neutralization. They help preserve foods. They work by killing bacteria through dehydration. Packing in salt was a common preservation method for pioneers.

D. Baking • The freshness and p. H of ingredients will affect the flavor, color, and texture of finished products.

• Chemical Leavening Agents: ingredients that are added to baked goods to lighten or aerate the finished product. Baking powder and baking soda work because they contain a base. When combined with an acid and moistened, neutralization occurs. The byproducts of this process are salt water and carbon dioxide

• Baking soda: Sodium bicarbonate is a salt. It is a base. When baking soda and an acid are combined in a baked product, carbon dioxide is released. Acids used include lemon juice, vinegar, sour cream, buttermilk and cream of tartar. It will leaven a product if acid is not present. Heat must be added for this reaction to occur.

Cream of tartar is one of the moisture activated dry acids often used in baking powders. When moisture is added, carbon dioxide is released. If over mixed or baking is delayed, the carbon dioxide can be worked out of the mixture.

• Baking powder: is a combination of baking soda, dry acids, and a filler. Most used in the US have two dry acids. One acid reacts when exposed to moisture and the other acid reacts when heated. These are called double-acting. The filler in baking powder absorbs moisture to help prevent the baking soda and acids from reacting prematurely.

• Ammonium Bicarbonate: a chemical leavening agent that does not form a solid product that remains in the dough. This is used in the baking of thin products such as cookies and crackers. This shape allows the unwanted ammonia gas to escape during baking.

• Batters and Dough: The more basic the batter for a particular type of cake is, the flatter and coarser the cake texture will become. Different cakes have different p. H needs. Angel food is the most acidic. Egg whites form a more stable foam when beaten if they are acidic. Chocolate cakes have a deeper, darker color and a smoother flavor if they are basic. German chocolate cake, a lighter colored cake, is more acidic because it is made with buttermilk

• Eggs and p. H: Eggs have a porous shell. Carbon dioxide which is an acidic gas dissolved in eggs, will gradually escape through the shell. As the gas escapes, the p. H will increase. Fresh egg whites can have a p. H as low as 5. 6. These egg whites will be thicker than egg whites from older eggs. The thicker the white, the more air it will trap. Older eggs have advantages. The loss of carbon dioxide releases the membrane around the egg white and shell. These are best for hard cooking because the pee will come off easier.

• p. H and Fruit Maturity: as fruits mature, acids develop. The acids improve juice quality, affect color development, and increase sugar content. The p. H of grapes is critical to successful wine making. As citrus fruits ripen, sugars increase and acids decrease. The ripening process and the changes associated with it stop once citrus fruits are picked. Citrus growers test the p. H of fruits to determine when to harvest for peak flavor.