pH, Acids, Bases, and Buffers

pH, Acids, Bases, and Buffers

Solutions

• Solute + Solvent = Solution• In nature, water is a major solvent.• Concentration – measured in moles• Molarity – 1 mol is dissolved in water to

equal 1 liter

pH

• A measure of the acidity and alkalinity of a solution

• Refers to the dissociation of water molecules.

• What does this show?

pH

• Constant – Kw = 1.0 x 10-14 (mol/L)2

– i.e. water dissociates at a rate of 1 molecule for every 554 million.

• At Kw there is an even split of H+ and OH-

– 1.0 x 10-7 each• pH is the negative log of the [H+] in mol/L

pH

• Since pH is calculated in log, a change in pH of 1 = a 10x change in the [H+]

• pH 1 is 10x smaller than a pH of 2.• pH 1 is 100x smaller than a pH of 3.

Problems

1. [H+] = 1.0 x 10-9 mol/L. Determine the pH.

2. [OH-] = 1.0 x 10-9 mol/L. Determine the pH.

3. Acid precipitation has lowered the pH of a particular lake to 4.0. What is the hydrogen ion concentration of the lake?

Acids and Bases

• Acids are molecules that release H+ when dissolved in water.

– Ex. Citrus Fruit, HCl– Acids make a solution more acidic.

• Bases are molecules that release OH- when dissolved in water.

– Lyme, Soap, Ammonia– Make solutions more basic.

Acids and Bases

• Neutral pH = 7• Acidic pH <7• Basic pH >7• Most biological fluids are within the range

of 6-8– Blood ~ pH of 7.4– Exceptions??

Buffers

• Substances that minimize changes in the concentrations of H+ and OH- in a solution.

• Buffers work by accepting H+ from solution when they are in excess and by donating H+ when they have been depleted.

• These buffers are usually composed of a weak acid and its base.

Blood

• pH = 7.4• Humans cannot survive for more than a

few minutes if the pH drops to 7 or rises to 7.8

• Buffers in the blood work to maintain the pH at or near 7.4– Ex. Carbonic Acid

Carbonic Acid

• Carbonic acid works with bicarbonate as a buffer.

• H2CO3 ↔ HCO3- + H+

Organic Compounds

Organic Compounds

• Compounds that contain carbon• Since carbon has 4 valence electrons, it

has great versatility. It is able to make 4 covalent bonds.

• The major elements of life are C, H, O, N, S, and P

Organic Compounds

• Carbon chains form the skeleton of most organic molecules.

• Hydrocarbons – consist of only carbon and hydrogen

• 3 Types of Isomers1. Structural2. Geometric3. Enantiomers

Structural Isomers

• Compounds with the same chemical formula but different structural formulas.

• Differ in the covalent arrangement of atoms

Geometric Isomers

• Have the same covalent partnerships, but differ in spatial arrangements

Enantiomers

• Molecules that are mirror images of each other.

• Enantiomers are important in the pharmaceutical industry.– 2 enantiomers of a

drug may not be equally effective.

From www.elmhurst.edu/~chm/vchembook/209optical.html

Organic Molecules

• 4 Types of Organic molecules1. Carbohydrates2. Lipids3. Nucleic Acids4. Proteins

Organic Molecules

Monomer Polymer

Carbs. monosaccharide polysaccharide

Lipids Glycerol and fatty acids

Nucleic Acids

nucleotide Nucleic Acid

Proteins Amino acid polypeptide

Carbohydrates

• Abbr. – CHO• Composed of C, H, and O• End in “-ose”• Ex. Glucose, Sucrose, Fructose, Starch• 1 CHO = Monosaccharide• CnH2nOn

• Glucose = C6H12O6

CHO’s

• monosaccharide + monosaccharide disaccharide + water

• This process is called Dehydration Synthesis– Water is removed from the molecules

(dehydration)– The two molecules are put together

(synthesis)

CHO’s

• MonosaccharidesGlucoseGalactoseFructose

• DisaccharidesMaltoseLactoseSucrose

Examples:Sucrose (table sugar) is composed

of glucose and fructose.

Polysaccharides

• Multiple CHO’s that are put together by dehydration synthesis.

• Four important polysaccharides

Structural Storage

Plants Cellulose Starch

Animals Chitin Glycogen

Lipids

• Include fats, oils, waxes, and steroids– All hydrophobic

• Consist of 1 glycerol molecule and 3 fatty acids.

• 2 types of fats: Saturated and unsaturated– Saturated fats – no C=C double bonds– Unsaturated fats – have C = C double bonds

Saturated and Unsaturated Fats

• 1 Glycerol molecule with 3 Fatty Acids

• Fatty acids are hydrocarbon chains

• Saturated fats have no double bonds between the carbons that make up the hydrocarbon chain.

• 1 Glycerol molecule with 3 Fatty Acids

• Have hydrocarbon chains that do contain at least one carbon-carbon double bond (C=C)