8.1 Acids and Bases

Characteristics of Acids

Acids (ie HCl, H2SO4, HCH3COO): are electrolytes react with many metals to form hydrogen gas and a

salt. cause indicators to turn colour

- blue litmus turns red- pink phenophthalein goes colourlesscolourless

neutralize bases

Characteristics of Bases

Bases (ie NaOH, Ca(OH)2, NH3 or NH4OH(aq)): are electrolytes form when active metals react with water cause indicators to turn colour

- red litmus turns blue- colourless phenophthalein goes pink

neutralize acids

The Arrhenius Theory of Acids and Bases Svante Arrhenius

(1859-1927)

-his theory described the activity of acids and bases when they were dissolved in water.

Science cracks me up!

The Arrhenius Theory of Acids and Bases

Acids ionize to form H+ ions in aqueous solution examples:

HCl(aq) H+(aq) + Cl-(aq)

H2SO4(aq) 2H+(aq) + SO4

2- (aq)

The Arrhenius Theory of Acids and Bases

Bases dissociate to form OH- ions in aqueous solution

examples:

NaOH(aq) Na+(aq) + OH-

(aq)

Mg(OH)2 (aq) Mg 2+ (aq) + 2OH-

(aq)

What factors affect Acid and Base strength?

Acid strength is determined by the concentration of H+ ions in solution.

(high concentration of H+ ions in solution, means a stronger acid)

Base strength is determined by the concentration of OH- ions in solution.

(high concentration of OH- ions in solution, means a stronger base)

What factors affect Acid and Base strength?

The most important factor is the degree of ionization or dissociation of the acid or base

Not all Acids and Bases are strong, for instance:A 1.00M HCl solution is a strong acid;A 1.00M HF solution is a weak acid.

A 1.00M NaOH solution is a strong base;

A 1.00M NH4OH solution is a weak base.

Remember: M = mol/L

Strong Acids Ionize 100% (>99%) upon dissolving in water. Because the acid ionizes 100%, the

concentration of H+ is the same as the concentration of the acid. (i.e. a 1.00M solution of HCl has an [H+] of 1.00M)

HCl, HBr, HClO4, H2SO4, HNO3, HI are strong acids

Note: [ ] = the concentration of

Weak Acids Ionize much less than 100% upon dissolving in water

(less than 5%) the concentration of H+ is much less than the

concentration of the acid (i.e. a 1.00M solution of HCH3COOH has a [H+] less than 1.00M)

examples include all of the other acids

Note: Acid Strength is not related to reactivity. HF is a weak acid, but it consumes flesh and bone.

Strong Bases dissociate 100% upon dissolving in water the concentration of OH- is the same as the

concentration of the base (i.e. a 1.00M solution of NaOH has a [OH-] of 1.00M)

examples include hydroxides of Group 1 metals and Group 2 metals below beryllium.

Weak Bases

Dissociate much less than 100% upon dissolving in water (less than 5%)

Because of this, the concentration of OH- is much less than the concentration of the base (i.e. a 1.00M solution of NH4OH has a [OH-] less than 1.00M)

examples include all of the other bases

8.2 pH of a Solution pH is a way of indicating the concentration of

H+ ions present in a solution pH = Power of Hydrogen

Calculating Ion Concentration and pH

[H+] = 10-pH

pH = -log [H+]

Type of Solution

pH [H+] Color of litmus

Acidic < 7.00 > 1x10-7 mol/L red

Neutral = 7.00 = 1x10-7 mol/L No change

Basic > 7.00 < 1x10-7 mol/L blue

pH and Ion Concentration

pH Scale

HOMEWORK

READ pg. 362 – 367 ANSWER # 1 – 3, 6, 7 on pg. 367 READ pg. 368 – 374 ANSWER # 1 – 6 on pg. 375