Mullis 1

Acids, Bases and Salts

• Acids give up hydrogen ions (H+) in a water solution.

• Bases give up hydroxide ions (OH-) in a water solution.

Mullis 2

Properties of Bases

• Bitter taste• Feel slippery if you touch them• pH > 7.0• Strong bases:

– Sodium hydroxide (NaOH)– Potassium hydroxide (KOH)

• Weak bases:– Sodium bicarbonate (NaHCO3)

Mullis 3

Properties of Acids• Sour taste • pH < 7.0• React with metals to form H2 gas• Strong acids:

– Sulfuric acid (H2SO4)– Hydrochloric acid (HCl)

• Weak acids: – Acetic acid (vinegar – CH3COOH))– Citric acid (in fruits)– Ascorbic acid (Vitamin C)

Mullis 4

Naming Acids

• Binary Acid = 2 elements (HCl)– Begin with hydro-.– Use name of 2nd element and end with –ic.– HCl is hydrochloric acid.

• Oxyacid = H + O + 3rd element (H2SO4)

– Usually incorporates the polyatomic ion name into the acid name.

– Written with H first, then the polyatomic ion.

– H2SO4 is sulfuric acid.

Mullis 5

Acid Strength• Strong acids ionize completely in water.

– Many H3O+ ions– Strong electrolyte

• Weak acids do not ionize completely in water.– Some H3O+ ions– Weak electrolyte– The ionized H3O+ ions are being bonded back to the

negative species (reverse reaction) at the same time some acid molecules are being ionized to form H3O+ ions .

• Strong and weak bases are similar, except ion involved is OH- instead of H3O+ .

Mullis 6

Acid-Base Systems

Type Acid Base Examples

Arrhenius H+ or H3O+ producer

OH- producer

HNO3 + H2O H3O+ + NO3-

NH3 + H2O NH4+ + OH-

Brønsted-Lowry

proton (H+) donor

proton (H+) acceptor

HCl + NH3 NH4+ + Cl-

Lewis electron pair acceptor

electron pair donor

BF3 + F- BF4-

BF3 is Lewis acid,

F- is Lewis base

Mullis 7

Brønsted-Lowry Acids

• Brønsted-Lowry acids donate a proton.

• A monoprotic acid donates one proton per molecule, such as HCl and HClO4.

• A polyprotic acid donates more than one proton per molecule, such as H2SO4 and H3PO4. – H2SO4 is a diprotic acid.

– H3PO4 is a triprotic acid.

Mullis 8

Conjugate acids and bases• The species remaining after a Brønsted-Lowry acid

gives up its proton is the conjugate base of that acid: Take off one H from the acid.

• The species remaining after a Brønsted-Lowry base accepts its proton is the conjugate acid of that base: Take off one H. Add an H to the base.

CH3COOH(aq) + H2O(l) H3O+(aq) + CH3COO- (aq)

acid base conjugate conjugate

(proton donor) acid base

Mullis 9

Examples of conjugate acids and basesHCO3

- (aq) + H2O(l) H2CO3 (aq) + OH- (aq)

base acid conjugate conjugate

(proton acid base

acceptor)

HF(aq) + H2O(l) H3O+(aq) + F- (aq)

acid base conjugate conjugate

(proton acid base

donor)

Mullis 10

Measuring Strength of Acids and Bases• pH is a measurement which indicates acidic or basic

strength, measuring the concentration of H+ ions.• More H+ ions = lower pH = acid.

• An indicator changes color depending on pH of a solution.

• pH paper is treated with indicators to change color when dipped in a solution.

1: acid 7: neutral 14: base

Mullis 11

Cl

The Hydronium Ion• Ionization is the creation of ions from a molecular

compound.– If the force of attraction between solvent molecules and

parts of the solute are stronger than the covalent bonds of the solute, the solute breaks into ions.

– In water, HYDRATION produces heat, which provides energy to break more covalent bonds.

• H + attracts other molecules or ions • In water, H+ becomes a proton bonded to the oxygen

of a water molecule.• The hydronium ion is H3O+.

ClOO+ +-+

H H H

H

H

H

Mullis 12

Salts

• An acid and base combined together react to neutralize each other.

• Neutralization is a process which produces produces that are not acids or bases.

• H+ and OH- make water.• The remaining reactants combine to make a salt.• A salt is an ionic compound made of a metal

and a nonmetal.• Soap and detergent are organic salts.

Mullis 13

Neutralization

HCl + NaOH NaCl + H2O

HNO3 + KOH KNO3 + H2O

H+(NO3)- + K+OH- KNO3 + H2O

ACID + BASE YIELDS SALT + WATER

saltacid base water

Mullis 14

Neutralization• The reaction between an acid and a base which produces a

salt and water. • Recall: A salt is an ionic compound: metal + nonmetal

which is likely to dissociate in water.• Ex: You take a dose of the antacid magnesium hydroxide,

Mg(OH)2, to relieve excess stomach acid, HCl.

• What is the chemical equation for this neutralization reaction?

HCl + Mg(OH)2 MgCl2 + H2O

These products are magnesium chloride and water.

Mullis 15

pH and acidity• pH is related to the concept of concentration of hydronium

ions found in water.• Water and all its solutions contain hydronium ions and

hydroxide ions.

• Acidic solutions: More H3O+ ions.

• Basic solutions: Fewer H3O+ ions / more OH- ions.

• If pH = 2:

H3O+ ion concentration = 0.01 M

OH- ion concentration = 0.000000000001 M• If pH = 12:

H3O+ ion concentration = 0.000000000001 M

OH- ion concentration = 0.01 M

Mullis 16

The pH scale

• pH stands for “power of hydronium ion.”

pH = -log [H3O+]

• pH value is the exponent on the power of 10 with its sign changed.

Mullis 17

pH examples

• Example 1: – 0.001 mol H3O+ = 1 x 10-3 mol H3O+

– Concentration is 0.001M

– pH = -log [H3O+] = -log (1x 10-3 ) = -(-3.0) = 3.0

– pH is 3.0 - This is an acid.

• Example 2: – 0.000 000 01 mol H3O+ = 1 x 10-8 mol H3O+

– Concentration is 0.000 000 01M

– pH = -log [H3O+] = -log (1x 10-8 ) = -(-8.0) = 8.0

– pH is 8.0 - This is a base.

Mullis 18

pOH

• pOH is the negative of the logarithm of the hydroxide ion (OH-) concentration.

pOH = -log [OH-]

pH + pOH = 14.0 at 25 deg. C

Mullis 19

Buffers• Why is the pH of some lakes unaffected by acid

rain even when they are downwind of big polluters?

• The lakes are surrounded by soils which neutralize the acidic precipitation.

1. One way to neutralize acid is to add a base. Limestone (CaCO3) is a weak base.

2. Another way to neutralize either an acid or a base is to add a buffer.

• A buffer is a substance or combination of substances capable of neutralizing limited quantities of either acids or bases.

Mullis 20

Buffers• Calcium carbonate around a lake contaminated with

acid rain would react this way:

CaCO3 + H3O+ Ca 2+ + HCO3- + H2O

• The polyatomic ion HCO3- acts as a buffer:

HCO3- + H3O+ 2H2O + CO2

HCO3- + OH- H2O + CO3

2-

• Another buffer is the hydrogen phosphate ion. Possible sources of this ion are Na2HPO4 and NaH2PO4.

H3O+ + H2PO4 2-

H2PO4 - + H2O