Chemical Compounds

Selected Portions of

Chapters 13 & 14

Acids, Bases, & Salts

Acid: a substance that produces a H3O+ (hydronium ion) when placed in water HCl + H2O H3O+ + Cl-

Base: a substance that produces OH- (hydroxide ion) when dissolved in water NaOH + H2O Na+ + OH- + H2O

NH3 + H2O NH4+ + OH-

Salt: an ionic compound formed from the positive ion of a base and the negative ion of an acid

Properties ofAcids & Bases

Acids pH less than 7 Taste sour Conduct an electric current Litmus* paper turns red Phenolphthalein* remains

colorless Release hydrogen gas when

reacting with metals Typically have an HX form

where X is a nonmetal (for example, hydrochloric acid is HCl)

Bases pH greater than 7 Taste bitter Conduct an electric current Litmus* paper turns blue Phenolphthalein* turns pink Feels slippery to the touch Typically have an XOH form

where X is a metal (for example, sodium hydroxide is NaOH)

Poisonous & Corrosive

(can destroy body tissue and clothing)

Examples of Acids & Bases

Acids Sodas (phosphoric

acid, carbonic acid) Fruit juices (citric acid) Battery acid (sulfuric

acid) Stomach Acid

(hydrochloric acid) Vinegar (acetic acid)

Bases Soaps (sodium

hydroxide a.k.a. lye or potassium hydroxide- mixed with fats)

Antacids (magnesium hydroxide, aluminum hydroxide)

Drain cleaners (sodium hydroxide)

Household cleaners (ammonia)

What is pH?

pH is an inverse measure of the concentration of H3O+ ions in a solution

It’s a way to measure how strong or weak an acid or a base is.

It is a scale that ranges from 0 to 14.

0------------------------7------------------------14

Strong Neutral Strong

Acid Base

pH scale

What’s an Indicator?

An indicator is a substance that is one color in an

acidic solution and another color in a basic solution. Example: phenolphthalein

The pH-sensitive compound cyanidin is present in many

plants, including cornflowers, poppies, and rhubarb. Cornflowers are blue because their sap is

basic, and cyanidin is blue in the presence of bases. Poppies have red flowers

because their sap is acidic. Rhubarbs are reddish in

color because of the oxalic acid they contain.

Strong vs. Weak

Strong Acids (when all the molecules of an acid break apart to

produce H+ ions)

Nitric acid Sulfuric acid Hydrochloric acid

Weak Acids (when only a few of the molecules of an acid break apart

to produce H+ ions)

Acetic acid Citric acid Carbonic acid Phosphoric acid

Strong Bases (when all the molecules break apart to produce OH- ions)

Sodium hydroxide Calcium hydroxide Potassium hydroxide

Weak Bases(when only a few of the molecules break apart to produce OH- ions)

Ammonia Magnesium hydroxide Aluminum hydroxide

What is a Buffer?

A buffer is a substance that can resist changes in pH even when acids and bases are added.

You have them in your blood and in your stomach.

Acid-Base Reactions

NEUTRALIZATION REACTION

Acid + Base Salt + Water

HCl + NaOH NaCl + H2O

acid base salt water

H2SO4 + 2KOH K2SO4 + 2H2O

acid base salt water

Reaction of a METAL and an ACID to form a salt and hydrogen gas

Mg + 2HCl MgCl2 + H2

metal acid salt hydrogen gas

Zn + H2SO4 ZnSO4 + H2

metal acid salt hydrogen gas

Acid-Base Reactions

Salts

Ionic compounds formed from the positive ion of a base and the negative ion of an acid

Examples:

sodium chloride (table salt)

calcium sulfate (in plasterboard)

sodium nitrate (preservative in foods, fertilizer)

calcium carbonate (limestone, chalk, in seashells)

ORGANIC COMPOUNDS

Covalent compounds composed of carbon-based molecules

Examples include: sugars, fats, proteins, nucleic acids

Each carbon atoms forms 4 bonds (it has 4 valence electrons)

Often bonds with hydrogen and oxygen, but may also join with sulfur, nitrogen, and phosphorus

BIOCHEMICALS: organic compounds made by living things

1. Carbohydrates - sugars

2. Lipids – fats, oils, waxes, and steroids

3. Proteins – made up of amino acids

4. Nucleic Acids – DNA, RNA

Ionic Compounds Ionic compounds are held together by ionic

bonds. Remember, an ionic bond is the force of attraction between two oppositely charged ions.

Ionic compounds are typically METAL-NONMETAL combinations.

Metals tend to lose electrons, giving them a positive charge.

Nonmetals tend to gain electrons, giving them a negative charge.

Ionic Compounds tend to…

be BRITTLE. Ions are often arranged in a repeating 3-D pattern called a crystal lattice.

have HIGH MELTING POINTS. Ionic bonds are strong, so it takes a lot of energy to overcome them.

Ionic Compounds tend to… DISSOLVE EASILY IN WATER (not all are

soluble in water, but most). Water is attracted to the ions and pulls them away from one another.

CONDUCT ELECTRICITY. When ionic compounds are dissolved in water, their solutions can usually conduct an electric current.

Covalent Compounds

Covalent compounds form when atoms share electrons.

Covalent compounds tend to be NONMETAL-NONMETAL combinations.

Covalent compounds exist as independent particles called molecules.

Covalent Compounds tend to…

NOT BE SOLUBLE IN WATER. Water molecules find themselves more attracted to one another than most covalent compounds. So they tend to separate out, like oil and water.

NOT CONDUCT ELECTRICITY. However, some covalent compounds (like acids) do.

Covalent Compounds tend to… have LOW MELTING POINTS. The force of

attraction between molecules is low, so it doesn’t take much energy to get them to melt.