Acids, Bases, and Salts

Chapter 18

Properties of Acids and Bases

• When dissolved in distilled water, they look the same

• Taste– Acid developed from the latin term acidus

(sour or tart)• Citric acid, lactic acid, carbonic acid, hydrochloric

– Bases taste bitter• Soap is an example of a base

Properties of Acids and Bases

• Touch– Dilute acids do not cause painful burns, but if

an open wound is exposed, then a sting is felt– Dilute bases do not sting (except in eyes)

• Typically feel smooth or soothing in low concentrations

– The higher the concentration for either acids or bases can result in painful burns

Properties of Acids and Bases

• Reactions with Metals– Acids react with several metals including Mg,

Zn, Fe, Al• See activity series p. 295

– Bases do not react with metals

Properties of Acids and Bases

• Electrical Conductivity– Both acids and bases are good electrolytes

(good conductors of electricity)– Distilled water is a poor conductor, but if an

acidic or basic solution is made, then the solution is quite conductive

– Electrolyte = substance that ionizes when dissolved in water

Properties of Acids and Bases

• Indicator = substance that turns 1 color in an acidic solution and a different color in a basic solution

• Litmus is the most common indicator.– Acids turn blue litmus paper RED or PINK– Bases turn red litmus paper BLUE

• Phenolphthalein is another example which changes colors at a specific level of acidity or basicity

Properties of Acids and Bases

• Neutralization Reaction = reaction between an acid and a base– If the proper amounts of acid and base are

added, they will completely neutralize each other.

• Based on MOLES

– Two products are always formed• H2O and an ionic salt

Arrhenius Definition

• Swedish chemist Svante Arrhenius• Developed an operating definition of acids

and bases according to the ions they produce when dissolved in water– Acids – dissociate in water to produce

hydrogen (H+ ions)• HCl, HNO3, H2SO4

– Bases – dissociate in water to produce hydroxide (OH- ions)

• NaOH, Ca(OH)2

Dissociation Examples

• Mg(OH)2 (aq)

• HBr (aq)

• HC2H3O2 (aq)

• CuOH (aq)

Neutralization examples

• NaOH (aq) + HCl (aq)

• Mg(OH)2 (aq) + HBr (aq)

• HC2H3O2 (aq) + CuOH (aq)

Arrhenius Definition Limitations

• Restricts acids and bases to water solutions– Acid and base reactions can occur in the gas

phase or can be dissolved in other solvents

• Chemicals such as ammonia (NH3) are bases, yet they do not have an OH- in the formula.

• So, a new “definition” had to be developed

Bronsted-Lowry Definition

• Acid – substance that can donate H+ ions• Base – substance that can accept H+ ions

• What is an H+ ion? How many protons, neutrons, and electrons?

• So…H+ can also be referred to as a ____.• Acid – substance that can donate _____.• Base – substance that can accept ____.

Polyprotic?

• Protic refers to “protons”

• How many protons does a monoprotic acid donate?

• How many protons does a diprotic acid donate?

• H3PO4 is an example of a _____ acid.

Hydronium Ions

• H+ ions are very attracted to the electrons of surrounding water molecules.

• H+ + H2O H3O+

• H3O+ = hydronium ion

ID the B-L Acids and Bases

• HCl(g) + H2O (l) H3O+ (aq) + Cl- (aq)

• NH3 (g) + H2O (l) NH4+

(aq) + OH- (aq)

Amphoterism

• A substance that can act as an acid or a base depending on the circumstances.

• See previous slide.

Conjugate Acid-Base pairs

• Technically, almost all acid-base reactions are reversible

• NH3 (g) + H2O (l) NH4+

(aq) + OH- (aq)

• Conjugate means coupled or joined

• “Conjugate” is used to describe the acid or base in the reverse reaction.

Determining the Strengths of Acids and Bases

• Vinegar contains 1M acetic acid– Spilling this on your skin has no great effect– Spilling 1 M HCl on your skin is a cause for

concern– Why?

• The strength of an acid or base is dependent upon the degree to which they dissociate.

Strong vs Weak

• HCl is a strong acid…so it is assumed that it dissociates completely

• HCl(g) + H2O (l) H3O+ (aq) + Cl- (aq)

lots lots

• Acetic acid is a weak acid…so not very much product is produced…it is reversible

• HC2H3O2 (aq) + H2O (l) H3O+ (aq) + C2H3O2

- (aq)

little little

Strong and Weak Acids

• Strong Acids• HCl• HBr• HI

• HNO3

• H2SO4

• Weak Acids

• HC2H3O2

• HCN

• HNO2

• HF

• H2CO3

Strong and Weak Bases

• Strong Bases• CaO• NaOH• KOH

• Ca(OH)2

• Weak Bases

• NH3

• CO32-

• PO43-

Acid Dissociation Constant

• Generic Weak Acid, formula = HA

• HA (aq) + H2O (l) H3O+ (aq) + A- (aq)

• How would the Keq be written?

• We also call this Ka, or the acid dissociation constant.

• What does a large Ka mean? Small Ka?

Base Dissociation Constant

• Generic base, formula = B

• B (aq) + H2O (l) HB+ (aq) + OH-

(aq)

• How would the Keq be written?

• We also call this the Kb, or the base dissociation constant.

• What does a large Kb mean? Small Kb?

Identifying Acids

• Binary Acids• Contain hydrogen and

one other element (usually group 6A or 7A)

• HCl• HF

• H2Se

• H2S

• Ternary Acids (Oxyacids)

• Contain hydrogen, oxygen, and one other element

• H2SO4

• HNO3

• H3PO4

Identifying Bases

• Most of the bases we will work with will have the OH- ion in the formula.

• NaOH

• Mg(OH)2

• Otherwise you should recognize ammonia (NH3) as a base even though it does not have an OH in the formula.

Naming Acids

• Typically, the name of the acid comes from the name of the ion it produces when it dissociates.

• Rule 1: If the name of an anion ends in -ide, the name of the acid that produces it includes the name of the anion, a hydro- prefix, and an –ic ending.

• Cl- is the chloride ion. The acid which produces it is HCl. Hydro- is placed in front, chlor is the root, and –ic is the ending.

• Hydro + chlor + ic acid = hydrochloric acid

Naming Acids

• Rule 2: If the name of an anion ends in –ate, the name of the acid that produces this anion has NO prefix (no hydro), but it does have an –ic ending.

• NO3- is nitrate.

• Nitr is the root and –ic is the ending.

• Nitr + ic acid = nitric acid

Naming Acids

• Rule 3: If the name of an anion ends in –ite, the name of the acid that produces this anion has NO prefix and has an –ous ending.

• SO32- is the sulfite ion.

• Sulf is the root and –ous is the ending.

• Sulfur + ous = Sulfurous acid

• Note…sulfurous, not sulfic…

Bases

• Name them just like all ionic compounds

• NaOH = sodium hydroxide

• Ca(OH)2 = calcium hydroxide

• Mg(OH)2 =

• Cu(OH) =

• Cu(OH)2 =

Try these acids

• Name• Phosphoric acid

• Nitrous acid

• Hydrofluoric acid

• Chloric acid

• Formula

• H2CO3

• H2Se

• HIO4