Acids & Bases Chapters 20 & 21

Properties of Acids & Bases React with metals Taste sour Bases: Taste bitter Feel slippery

Chemical Composition Acids produce Hydrogen ions (H+) in aqueous solution. Ex: HCl, H2SO4, HNO3 Bases produce Hydroxide ions (OH-) in solution. Ex: NaOH, KOH, Mg(OH)2

Neutralization Acids & Bases react to form water and a salt (ionic compound). When combined in the correct amounts, all the OH- and H+ ions combine to form water molecules. The resulting solution is neutral.

pH (percent hydrogen) Acids and bases are measured using the pH scale. Solutions with a pH of 7 are considered neutral (equal # of H+ and OH- ions)

Solutions with a pH lower than 7 are acidic as they contain more H+ ions than OH-. Solutions with a pH above 7 are basic as they contain more OH- ions than H+.

The pH scale pH is a logarithmic scale, similar to the Richter scale used to measure earthquakes. An acid with a pH of 2 is ten times stronger than a pH 3 solution. An acid with a pH of 1 is ten times stronger than a pH 2 solution.

pH is dependent upon the concentration (molarity) of H+ ions. pH = -log[H+] ([X] means molarity of X)

Examples Find the pH of a 1.0 x 10-3M solution of HCl. 3 Find the pH of a 2.5 x 10-5M solution of HNO3 4.6

[H+] = 10^ (-pH) Find the [H+] of a solution with a pH of 6.4 = 4.0x10-7 M Find the [H+] of a solution with a pH of 9.1 = 7.9x10-10 M Find the [H+] of a solution with a pH of 2.7 = 2.0x10-3 M

pOH pOH is the opposite of pH. A pH of 7 = pOH of 7 A pH of 8 = pOH of 6 A pH of 6 = pOH of 8 pOH = 14 – pH

pOH pOH = - log[OH-] What is the pOH of a solution of a 3.4x10-3 M NaOH? [OH-] = 10^ (-pOH) What is the [OH-] of a solution with a pOH of 5.5?

Acid – Base Indicators An indicator is a valuable tool for measuring pH b/c it will change color depending on the pH Page 590 – Figure 20.8 Litmus paper is an indicator

Arrhenius Acids & Bases Arrhenius Acids – contain H+ ion Arrhenius Base – contain OH- ion A monoprotic acid has 1 H+ A diprotic acid has 2 H+ A triprotic acid has 3 H+

Bronsted Acids & Bases Bronsted-Lowry Acids: a hydrogen ion donor Bronsted-Lowry Base: a hydrogen ion acceptor NH3 (ammonia) is a Bronsted-Lowry base.

Conjugate Acids & Bases A conjugate acid is the particle formed when a base gains an H+ ion A conjugate base is the particle formed after an acid gives up its H+ ion

Lewis Acids & Bases A Lewis acid can accept a pair of electrons to form a covalent bond A Lewis base donates a pair of electrons to form a covalent bond

Strength of Acids & Bases A strong acid ionizes completely in solution A weak acid ionizes only partially in solution Strong bases dissociate completely in solution

This is a neutralization reaction Acid-Base Reactions When an acid and a base react, they will neutralize to form water (HOH) and a salt - double displacement reaction This is a neutralization reaction HCl + NaOH  HOH + NaCl

Titration The concentration of an acid or base in solution can be determined by a neutralization reaction An indicator is used to tell when the pH is neutral

Steps of Titration A measured volume of acid of unknown concentration is added to a flask Indicator is added Measured volume of base of known concentration is added until a color change occurs

Titration Problem A 25ml soln. of HCl is neutralized by 18ml 1.0M NaOH. What is the concentration of the acid? M base = 1.0M Volume of Base = 18mL Volume of Acid = 25mL

Titration Problem cont’d MaVa = MbVb M = molarity, V = volume, a = acid, b= base (25mL)(Ma)=(18mL)(1.0M) (Ma) = (18 x 1.0) / (25) Ma = 0.72M