Unit 4: Acids and Bases Chapter 8

Section 1 Objectives Describe the ionization of strong acids in water and the dissociation of strong bases in water. Distinguish between solutions of weak acids or bases and solutions of strong acids or bases. Relate pH to the concentration of hydronium ions and and hydroxide ions in a solution.

What Are Acids? Substances that have a pH lower than 7 Substances that have more H+ ions than OH- ions Substances that have a sour taste When dissolved in water, they ionize to form H+ ions These H+ ions join with the water molecules to form H3O+ (hydronium) ions Turn blue litmus paper red

Strong v. Weak Acids If an acid ionizes completely in water, it is a strong acid and has a very low pH The farther from 7 the pH is, the stronger the substance If a substance does not ionize completely in water, it is a weak acid and has a pH closer to 7 Strong acids are able to conduct electricity when dissolved in water and are called electrolytes

Common Acids ACID FORMULA STRENGTH USES Hydrochloric acid HCl Strong Cleaning, treating metal, adjusting the pH of pools, digestion Sulfuric acid H2SO4 Fertilizer, industrial chemical, car batteries Nitric acid HNO3 Fertilizers and explosives Acetic acid CH3COOH Weak Chemicals, plastics, pharmaceuticals, vinegar Formic acid HCOOH Dyes, stinging ants Citric acid H3C6H5O7 Flavorings, soft drinks, citrus fruits

What Are Bases? Substances that have a pH higher than 7 Substances that have more OH- ions than H+ ions Substances that taste bitter and feel slippery When dissolved in water, they ionize to form OH- ions Strong bases (those with a pH farther from 7) are more conductive of electricity than weak bases (those with a pH near 7) Not all bases contain OH- ions; some just produce OH- ions when dissolved in water

Common Bases BASE FORMULA STRENGTH USES Potassium hydroxide KOH Strong Soap, absorbing CO2, dyes Sodium hydroxide NaOH Soap, petroleum refining, cleaning drains, synthetic fibers Calcium hydroxide Ca(OH)2 Treating acidic soil and lakes, making mortar and cement Ammonia NH3 Weak Fertilizer, making nitric acid, cleaning Methylamine CH3NH2 Dyes, medicines, tanning leather Aniline C6H5NH2 Dyes, varnishes, solvent

What is pH? Determined by using an indicator, such as litmus paper A measure of the concentration of hydronium (H3O+) ions pH is very important in living organisms, as many functions can only occur within a very specific range of pH pH scale ranges from 0 – 14. Acids are below 7, bases are above 7, and neutral substances (such as water and salts) are right at 7.

The pH scale is based on the power of 10 An acid with a pH of 3 is 10x stronger than an acid with a pH of 4 A base with a pH of 9 is 100x weaker than a base with a pH of 11 A small difference in pH can mean a very large difference in acidity or basicity

Calculating pH Concentrations of substances in a solution are written using the units of molarity, or moles of substance per liter of solute So, if the concentration of H3O+ ions in pure water is 0.0000001 mol/L, it can be written as 10 ^-7 M The pH is the negative of the power of 10 In this example, the pH of the substance would be 7

Practice What is the pH of a 10^-4 M solution of bromic acid (HBr)? What is the pH of a 0.01 M solution of nitric acid (HNO3)? HBr = 4 HNO3 = 2