Acids, Bases, and Salts

Acid Base (Alkali)

Litmus color

Phenolphthalein color

pH range (from universal indicator

paper)

Taste

Formula component

Other?

Characteristics of Acids and Bases

Substance

Acid Base (Alkali)

Neutral

Vinegar

Epsom salts

Lye

Aspirin

Baking soda

Windex (window cleaner)

Apple juice

Bubble bath

Washing soda

Vitamin C

Household Acids and Bases

CSSI 2010 PGCC Barbara A. Gage

1.0 battery acid (sulfuric acid) 1.8-2.0 limes 2.2-2.4 lemon juice 2.2 vinegar (acetic acid) 2.8-3.4 fruit jellies 2.9-3.3 apple juice, cola 3.0-3.5 strawberries 3.7 orange juice 4.0-4.5 tomatoes 5.6 unpolluted rain 5.8-6.4 peas 6.0-6.5 corn 6.1-6.4 butter 6.4 cow's milk 6.5-7.5 human saliva 6.5-7.0 maple syrup 7.0 distilled water

7.3-7.5 human blood 7.6-8.0 egg whites 8.3 baking soda8-9 laundry detergents 9.2 borax 10.5 milk of magnesia 11.0 ammonia 12.0 lime water 13.0 lye 14.0

pH of Some Household Materials

Indicators

• What color are most acids and bases?• What do litmus, phenolphthalein, and

universal indicator paper have in common?

• These substances change color depending on whether a solution is acidic, basic or neutral.

• They are called indicators.

Are Acids and Bases Ionic?

• How can you tell if a substance is ionic?

A solution of the substance will conduct electricity

• Many bases are ionic compounds that contain the polyatomic ions OH-, HCO3

- or CO32-

The electrical conductivity of ionic solutions.

Are Acids and Bases Ionic?

• Acids are held together by covalent bonding (H form covalent bonds only) so should they conduct electricity?

• But acids do conduct so what’s happening?• The hydrogen in acids is attached to an

electronegative element so the bond is very polar. When you put the acid in water the hydrogen will “ionize” and leave its shared electrons with the other atom.

Acids

• HCl + H2O H3O+ + Cl-

hydronium ion

Strong and Weak Acids and Bases

• If an acid or base solution is a strong conductor it is called a strong acid or strong base.

• If the solution is a poor conductor it is called a weak acid or base.

• Strength of acids or bases IS NOT THE SAME AS concentration.

Strong acid: HA(g or l) + H2O(l) H3O+(aq) + A-

(aq)

The extent of ionization for strong acids.

H+ and H2O H3O+ (hydronium ion)

The extent of ionization for weak acids and bases.

Weak acid: HA(aq) + H2O(l) H3O+(aq) + A-

(aq)

Weak acid are only partly ionized. Many intact molecules remain.

AcidsStrong

hydrochloric acid, HCl stomach acidhydrobromic acid, HBr

nitric acid, HNO3 used to make explosivessulfuric acid, H2SO4 battery acid

perchloric acid, HClO4 used to digest plant matterWea

k

hydrofluoric acid, HF used to etch glassphosphoric acid, H3PO4 naval jelly, to remove rustacetic acid, CH3COOH (or HC2H3O2) vinegar

ionizes completely in water

ionizes partially in water

carbonic acid, H2CO3 in carbonated drinks

Bases (or alkalis)Strong

Weak

sodium hydroxide, NaOH

calcium hydroxide, Ca(OH)2

potassium hydroxide, KOH

strontium hydroxide, Sr(OH)2

barium hydroxide, Ba(OH)2

ammonia, NH3 (NH4OH)

Moderate

Dissociates completely Dissociates completely but is not very soluble

aluminum hydroxide, Al(OH)3

magnesium hydroxide, Mg(OH)2

Dissociates partially

carbonates, CO32-

bicarbonates, HCO31-

Acid and Base Definitions

• Arrhenius• Acid = compound that forms

hydrogen (H+) ions in water• Base = compound that forms

hydroxide (OH-) ions in water

Acid and Base Definitions

• Bronsted-Lowry• Acid = proton donor (H+ is a proton)• Base = proton acceptor (picks up an

H+)

Acid Anhydrides

• Non-metal oxides react with water to form acidic solutions

CO2 (g) + H2O (l) H2CO3 (aq)

N2O5 (s) + H2O (l) 2 HNO3 (aq)

SO3 (g) + H2O (l) H2SO4 (aq)

Dissolved non-metal oxides cause acid rain. This is why tap/distilled water has a pH lower than 7!

Basic Anhydrides

• Metal oxides react with water to form alkaline solutions

Na2O (s) + H2O (l) 2 NaOH (aq)CaO (s) + H2O (l) Ca(OH)2 (aq)Al2O3 (s) + 3 H2O (l) 2 Al(OH)3 (aq)

Lime (CaO) is used on lawns and is converted to Ca(OH)2 when it rains. CaO is less hazardous to handle.

What Happened When Acids and Bases are Mixed?

• What did you uncover when these materials are mixed?

• How could you tell?

• Acid + Base Water and a “Salt”

• A “salt” is an electrolyte that is generally not an acid or base.

An aqueous strong acid-strong base reaction on the atomic scale.

MX is a “salt” – an electrolyte that is not an acid or base

Acid-Base Reactions

• HCl + NaOH

• H2SO4 + Mg(OH)2

• HBr + Al(OH)3

• HCl + NaHCO3

Acid-Base Reactions

• HCl + NaOH NaCl + H2O

• H2SO4 + Mg(OH)2 MgSO4 + 2H2O

• 3 HBr + Al(OH)3 AlBr3 + 3 H2O

• HCl + NaHCO3 NaCl + H2O + CO2

Acid-Base Reactions

• Acid-base reactions are also called neutralization reactions.

Why?

• If you mix the right proportions of acid and base the solution should end up neutral.

Antacids

• What happens when you produce too much stomach acid?

Acid may reflux into the unprotected esophagus and cause a burning sensation

• Antacids (anti-acids) neutralize excess stomach acid.

Antacids

• Tums, Rolaids: 2HCl + CaCO3 CO2 + CaCl2 + H20

• Milk of Magnesia, Mylanta, Maaolox2HCl + Mg(OH)2 MgCl2 + 2H2O

(and Al(OH)3 in Maaolox)

• Alka-Seltzer:HCl + NaHCO3 NaCl + CO2 + H2O

(and KHCO3)

An acid-base titration.

Start of titrationExcess of acid

Point of neutralization

Slight excess of base

• What about pH? Why is the pH of a neutral solution = 7?

• First we need to talk about what happens in pure water.

[H3O+][OH-]Kw =

A change in [H3O+] causes an inverse change in [OH-].

= 1.0 x 10-14 at 250C

H2O(l) + H2O(l) H3O+(aq) + OH-(aq)

In an acidic solution, [H3O+] > [OH-]

In a basic solution, [H3O+] < [OH-]

In a neutral solution, [H3O+] = [OH-]

The pH values of some familiar

aqueous solutions.

pH = -log [H3O+]pOH = -log [OH-]pH + pOH = 14

Figure 18.6 The relations among [H3O+], pH, [OH-], and pOH.

Out of Range pH’s

• Can a pH be lower than 0 or higher than 14?

Yes!• When you have solutions that are more

concentrated than 1 M the value of pH will be out of the normal range

• 6M HCl pH = -log[2.0] = -0.8• 1.5 M NaOH pH = 14.2

Buffers

• Solutions that resist change in pH• Can maintain any pH value between 0

and 14 (not just neutral pH 7)• Composed of a weak acid and a salt

made from the weak acid or weak base and salt made from the weak base

• Examples: HC2H3O2 and NaC2H3O2

NH4OH and NH4Cl

Buffers

Reaction with acid:HC2H3O2 + C2H3O2

- + H+ HC2H3O2 + HC2H3O2

Reaction with base:HC2H3O2 + C2H3O2

- + OH- C2H3O2

- + C2H3O2- + HOH

A buffer regenerates it’s own components. The pH it maintains depends on the ratio of salt to acid (or base) and the nature of the acid (or base).