Acids and Bases

Acids & Bases● There are 3 common definitions of acids and bases.

– Arrhenius definition – acids increase H+ concentration, bases increase OH- concentration

– Brønsted-Lowry definition – acids are proton donors, bases proton acceptors

– Lewis definition – acids accept a pair of electrons

● Arrhenius acid- a substance that produces an H+ (or H3O+) cation in

solution.

● HCl(aq) → Cl-(aq) + H+(aq)

● Acids dissolved in water create hydronium ions● H+ + H

2O → H

3O+

● Arrhenius Base- a substance that produces an OH- anion in solution.● NaOH(s) → Na+(aq) + OH-(aq)

Physical Properties of Acids

Have a sour taste.

Physical Properties of AcidsTurns blue litmus to red.

Turns methyl orange to red.Indicator - a chemical compound that change color when

the acidity of the solution changes.

Physical Properties of AcidsWill react with:

some metals to produce a salt and H2 gas

metal oxides to produce a salt and H2O.

metal carbonates to produce a salt, H2O, and CO2.

bases to produce a salt and H2O.

Mg + 2HCl MgCl2 + H2

MgO + 2HCl MgCl2 + H2O

MgCO3 + 2HCl MgCl2 + H2O + CO2

Mg(OH)2 + 2HCl MgCl2 + 2H2O

AcidsAre electrolytes.

electrolytes are substances that conduct an electric current when dissolved.

Strong AcidsCommon strong acids:

hydrochloric acid, HClhydrobromic acid, HBrnitric acid, HNO3

chloric acid, HClO3

sulfuric acid, H2SO4

Common weak acidsAcetic acid, HC2H3O2

Hydrofluoric acid, HF

Physical Properties of BasesHave a bitter taste.

Coffee itself is acidic, but it contains an alkaline compound – caffeine – which contributes to its bitter taste.

Physical Properties of BasesFeel slimy or slippery to the touch.

Physical Properties of BasesTurns red litmus to blue.Turns methyl orange to yellow.Turns phenolphthalein to pink.

Litmus pH scale.

Physical Properties of BasesReact with acids to produce salt and H2O.

HCl + NaOH NaCl + H2O

Physical Properties of BasesAre also electrolytes.

Strong BasesLike strong acids, strong bases ionize completely.

Strong bases = soluble hydroxideslithium hydroxide, LiOHsodium hydroxide, NaOHpotassium hydroxide, KOHcalcium hydroxide, Ca(OH)2

strontium hydroxide, Sr(OH)2

barium hydroxide, Ba(OH)2

All other bases, including NH3, are weak.

Hydrogen and Hydronium Ions

H

H H

H H

H H

H

Acid

+

+

-

-

H

Hydrogen ion (proton)

Hydronium ion, H3O+1

H

H

HHH

H H

H

HH

H H

H H

H

H

H

H

H

H

Hydroxide Ions

HBase

H+

Hydroxide ion, OH-1

H

HH

H

HH

H H

H

HH H

HH

HH

HH

HH

H

H

H

H

HH

H H

HH

HHH

H

Review

pH ScaleTraditionally 0 - 14.

Can have pH < 0 or > 14.

pH < 7 Acidic solution.pH = 7 Neutral solution.pH > 7 Basic solution.

pH Scale

Acidic Basic

0 1 2 3 4 5 6 7 8 9 10

11

12

13

14

pH and ConcentrationpH = the “power” of hydrogen

– it is the strength of the H+ ion– Concentration is measured using Molarity

However, brackets are used to indicate concentration• [H+] = the concentration of the H+ ion in solution

pH and concentration formulapH = -log [H+]

[H+] = Molar concentration of H+ ionExample: What is the pH of a 0.0045 M HCl solution?

Note: the concentration of H+ is the same as HCl, because there is only one H+ is produced

pH = - log (0.0045M)pH = 2.35

** double check- is this pH good for an acid?

pH and pOHpOH is the “power of hydroxide”

Formula: pOH = - log [OH-]Example: What is the pOH of a 3.41 x 10-4 M NaOH solution?

pOH = -log[OH-]= -log[3.41 x 10-4 M]= 3.47

pH and pOHBases have pH values too

Water itself is an acid and a base[H+] and [OH-] are equal

H2O → H+ + OH-

Therefore: pH + pOH = 14 - Page 3 of NC Ref. Tables

· What is the pH of the base in the previous example?

Formula: pH + pOH = 14 - Page 3 of NC Ref. Tables

pH + 3.47 = 14

pH = 10.53

** is this a good pH for a base?