Chemical Compounds

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

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) Properties ofAcids & Bases Poisonous & Corrosive (can destroy body tissue and clothing)

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) Examples of Acids & Bases

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

Acid-Base Reactions 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

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 CArbon 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

CArbon

BIOCHEMICALS: organic compounds made by living things • Carbohydrates - sugars • Lipids – fats, oils, waxes, and steroids • Proteins – made up of amino acids • 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.

Chemical Compounds