Chapter 23- Acids, Bases, and Salts - Mrs. Perry's ...



Chapter 22- Acids, Bases, and Salts

Section 1- Acids and Bases

Acid- a substance that produces hydrogen ions (H+) in a water solution

All acids have at least one hydrogen atom; this hydrogen atom can be removed when dissolved in water

Examples:

Hydronium ion- is H3O+.

When an acid dissolves in water, H+ ions interact with water molecules to form H3O+

Properties of acids

• Sour taste

• Can burn skin

• Corrosive

• React with some active metals to form hydrogen gas and some other compound

• Conduct electricity

• Turn litmus red

• pH of less than 7

Common acids and their uses

• Acetic Acid (CH3COOH) is in vinegar; used in preserving foods

• ASA [Acetylsalicylic acid, C9H8O4] is main component of aspirin; used in pain relievers

• Ascorbic acid (C6H8O6) is vitamin C; found in citrus fruits

• Carbonic acid is in soda pop; it makes pop carbonated. It is also dissolves rocks and is involved in cave formation

• Hydrochloric acid (HCl) is in your stomach to break down food. It is used in industry to clean steel in a process called pickling

• Lactic acid (C3H6O3) is produced in muscles when you exercise too much too fast. It is also what makes milk go sour; in yogurt & buttermilk.

• Nitric acid (HNO3) is colorless but turns yellow when exposed to light. Used in making fertilizers. Very nasty stuff.

• Phosphoric acid (H3PO4) is in soda pop, detergents, and fertilizers. Detergents that contain phosphates (PO43-) create pollution.

• Sulfuric acid (H2SO4) is in car batteries. Will pull water from the air if left open. Used in making paper. Very nasty stuff also.

Detecting Acids and bases

Indicator- organic compound that changes color in acid and base

Example: Litmus paper is red in an acid and blue in a base

pH paper

phenolphthalein solution

Base- Any substance that forms hydroxide ions, OH1-, in a water solution

A base is also defined as any substance that accepts H+ from acids

Properties of Bases:

– Crystalline solids in undissolved state

– Bitter taste

– Slippery feel

– Can burn skin

– Corrosive

– Conduct electricity

– pH > 7

– Litmus paper ( Blue

Common bases and their uses

• Aluminum hydroxide [Al(OH)3] is a sticky gel-like material used as a water purifyer; used as an antacid, in water purification, and making fabrics.

• Calcium hydroxide [Ca(OH)2] is in “lime” for gardens and lawns. Used in plaster and making leather products.

• Magnesium hydroxide [Mg(OH)2] is in antacids and laxatives. In “milk of magnesia”.

• Sodium hydroxide [NaOH] is called “lye” and “caustic soda”. Used in making soap, oven cleaner, drain opener, fabrics, paper. Very nasty stuff

• Ammonia [NH3] is very bad smelling; can damage lungs. Used in cleaners, fertilizers, and to make fabrics.

Solutions of acids and bases

Ionization of acids

• The acid ionizes (or separates) into ions and the hydrogen atom combines with a water molecule to form hydronium ions (H3O+).

• The negative areas of water attract to the positive H in the acid to form H3O+.

•

Dissociation of bases

• When bases dissolve in water, the negative areas of nearby water molecules attract to the positive ion in the base.

• The positive areas of nearby water molecules attract to the –OH of the base.

Ammonia (NH3) is a base that does NOT contain OH1- ions

• It causes the ionization of water

• Ammonia molecule attracts a hydrogen ion from a water molecule, forming an ammonium ion (NH4+).

Self Check

1. What does an acid produce in solution?

2. What changes color in acids and bases? What category of chemicals is it?

3. A base forms what in what in a water solution?

4. What is the pH range for acids?

5. What is the pH range for bases?

6. Identify three important bases and describe their uses.

7. If an acid donates H+ and a base produces OH-, what compound if likely to be produced when acids react with bases?

Section 2- Strengths of acids and bases

• The strength of an acid or base depends on how many acid or base particles dissociate into ions in water.

Strong acid- when it dissolves in water, nearly all the acid molecules dissociate into ions. Examples: HCl, HNO3, and H2SO4.

• A strong acid solution conducts more current because more ions are formed. Light bulb would be bright.

Weak acid- when it dissolves in water, only a small fraction of the molecules dissolve in water. Examples: acetic acid and carbonic acid

• A weak acid solution does not conduct as much current because less ions are formed. Light bulb would be dim.

• Strong acid - nearly all the acid molecules dissociate into ions.

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• Weak acid - only a small fraction of the molecules dissolve in water.

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Strong base- dissociates completely in solution

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Weak base- one that does not dissociates completely

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Strength and concentration are different concepts.

• Strong and weak refer to the degree to which an acid or base ionizes.

• Dilute and concentrated are used to indicate the concentration of a solution, which is the amount of acid or base dissolved in the solution.

• You can have a dilute solution of a strong acid

• You can have a concentrated solution of a weak acid

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pH - measure of the concentration of H+ ions in a solution.

• The greater the H+ concentration ( more acidic

• Lower the H+ concentration ( more basic

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• The pH scale ranges from 0 to 14.

• pH less than 7 are acidic (more H+).

• pH greater than 7 are basic (More OH-).

• pH of 7 is neutral (H+ ions and OH- ions are equal)

• Each value is 10x more or less acidic than the next

• pH of blood must remain between 7.0 and 7.8

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Detecting Acids and Bases

pH can be determined by using:

1. pH paper which changes color

2. pH meter

Indicators can tell if it’s acid or base, but cannot tell you a pH

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Buffers- solutions containing ions that react with additional acids or bases to minimize their effects on pH. Your blood has buffers that make it resistant to changes in pH.

Self Check

1. What is the difference between a strong acid and a weak acid?

2. What is the difference between the terms “strength” and “concentration”?

3. The pH of a solution is a measure of the concentration of _________ in the solution.

4. (T/F) The lower the H+ concentration, the more basic the solution.

5. What is the range of the pH scale?

6. Describe what determines the strength of an acid or a base.

7. Explain how to make a dilute solution of a strong acid.

8. Explain how electricity can be conducted by solutions.

9. Describe pH values of 9.1, 1.2, and 5.7 as basic, acidic, or very acidic.

10.How much more acidic is a solution of pH 2 than a solution of pH 4?

Section 3- Salts

Neutralization- is a chemical reaction between an acid and a base that takes place in a water solution

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Salt- is a compound formed when the negative ions from an acid combine with the positive ions from a base.

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Neutralization Reaction:

Acid + Base ( Salt + Water

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Common Salts and their uses

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Titration- process in which a solution of know concentration is used to determine the concentration of another solution.

Natural indicators

Many natural substances are acid-base indicators.

ex) red cabbage, radishes, roses

Soaps- are organic salts. The nonpolar organic chain of carbon atoms on one end and either a sodium or potassium salt of a carboxylic acid group at the other end

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Self Check

1. Describe a neutralization reaction. What are the products of such reactions?

2. A compound formed when the negative ions from an acid combine with the positive ions from a base is called a ________________.

3. (T/F) Many natural substances are acid-base indicators.

4. _______________ is the process in which a solution of known concentration (standard solution) is used to determine the concentration of another solution.

5. A chemical reaction between an acid and a base that takes place in a water solution is called a(n) __________________.

6. Explain how the composition of detergents differs from that of soaps

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