Acids & Bases

PropertiesAcid-Base TheoriesAcid-Base Reactions

Properties

Both conduct electricity (electrolytes) because they break apart to some degree in water.Acids produce H+ (proton) in water.Bases produce OH- (hydroxide) in water.

Samples:Acids: vinegar(acetic acid), lactic acid in sour milk, citric acid, Bases: ammonia, lye (NaOH), Milk of Magnesia Mg(OH)2.

More on Acids

1. Sour taste. NEVER taste acids in lab situations.

2. Change color of indicators.3. Some acids react with metals & release H2

gas.4. Acids react with bases to produce salt &

water. When neutralization occurs, #1.-#3 disappear.

5. Conduct electric current.

Neutralization Reaction

Acid + Base --> Salt + WaterHCl + NaOH --> NaCl + H20

H2SO4 + Ca(OH)2 --> CaSO4 + 2H20

Acid Nomenclature

• Binary Acids contain Hydrogen and another element:

• Hydro + root of 2nd element + ic– HF hydrofluoric acid– HCl hydrochloric acid– HBr hydrobromic acid– HI hydroiodic …– H2S hydrosulfuric …

Oxyacids• Contain H, O, and a 3rd element. More are

listed in your book.

Common Industrial Acids

• Sulfuric• Nitric• Phosphoric• Hydrochloric• Acetic

Bases

• Bitter taste (NEVER taste bases in labs).• Change the color of indicators.• Slippery feel (dilute bases, don’t touch

concentrated bases)• React with acids to produce salt & water• Conduct electric current.

Arrhenius Acids & Bases

An Arrhenius Acid is a chemical compound that increases the concentration of hydrogen ions (H+) in aqueous solutions through ionization.An Arrhenius Base is a chemical compound that increases the concentration of hydroxide ions (OH-) in aqueous solutions through dissociation forming ions.

• HNO3 (l) + H20 (l) --> NO3- (aq) + H30+ (aq)

• When put in water, HNO3 , ionizes and the charged particles formed can conduct electricity.

• The amount of H30+ (hydronium) produced is an indication of the acid’s strength.

Strong Acids ionize completely in water.

Strong Acids:• HI• HClO4

• HBr• HCl• H2SO4

• HClO3

Weak Acide release few hydrogen ions in water.

Weak Acids:• HSO4

-

• H3PO4

• HF• CH3COOH

• H2CO3

• H2S

• HCN• HCO3

-

For Bases, the strength depends on how it dissociates

Strong Bases ionize completely.

Strong Bases• Ca(OH)2 --> Ca2+ + 2OH-

• Sr(OH)2

• Ba(OH)2

• NaOH• KOH• RbOH• CsOH

Weal Bases ionize slightly.Weak Bases• NH3 + H2O NH4

+ + OH-

• C6H5NH2

“ “ means the reaction is

reversible

Acid-Base Theories

Bronsted-Lowry Acids donate protons (H+)Molecules or ions can donate protons.HCl + NH3 NH4

+ + Cl-

H+

NH4+ + NH2 2NH3

Donor Acceptor

The HCl is a Bronsted-Lowry Acid. It donates a proton to water producing H3O+.

Water can act as a Bronsted-Lowry Acid also as in the following reaction:

H2O (l) + NH3 OH- + NH4+

HCl + H2O H3O+ + Cl-

H+

• In the above reaction

Bronsted-Lowry Bases

accept protons. In the equation below, ammonia is the base, because it accepts the proton to become an ammonium ion.

HCl + NH3 NH4

+ + Cl-

acid base

Mono- and Polyprotic Acids• Monoprotic acids can only donate one proton

per molecule. Ex.: HCl, HNO3

• Polyprotic acids can donate 2 or more protons per molecule. Ex.: H2SO4, H3PO4

• For polyprotic acids the donations occur in stages, losing one H+ at a time.

Lewis Acids and Bases

• Arrhenius and Bronsted-Lowery definitions have some limitations. Lewis classification is based on bonding and structure including substances without hydrogen. The Lewis classification is more complete than the other 2 methods.

A Lewis acid

is an atom, ion or molecule that accepts an electron pair to form a covalent bond.

Dot notation

Structural formula – a bar represents what?A pair of shared electrons.

A Lewis base

is an atom, ion, or molecule that donates an electron pair to form a covalent.

Lewis Acid-Base Reaction• is the formation of one or more covalent

bonds between an electron-pair donor and an electron-pair acceptor.

Pair of donated electrons

14.1 and 14.2 Assignment:

14.1: 476/1-4 due wed.14.2: 482/1,2

491/12-18•Samples are done on the next 2 frames.

491/15. Dilute HCl(aq) and KOH(aq) are mixed in chemically equivalent quantities.

a) Write the formula equation for the reaction.HCl(aq) + KOH(aq) --> KCl(aq) + H2O(l)

b) Write the overall ionic equation.H3O+(aq) + Cl-(aq) + K+(aq) + OH-(aq) -->

K+(aq) + Cl-(aq) + 2H20(l)

c) Write the net ionic equation.H3O+(aq) + OH-(aq) --> 2H20(l)

491/17a. Write the formula equation and net ionic equation for this reaction.

Formula equation for: Zn(s) + HCl(aq) --> Zn(s) + 2HCl(aq) --> ZnCl2(aq) + H2(g)

Overall ionic equation:Zn(s) + 2H3O+(aq) + 2Cl-(aq) -->

Zn2+(aq) + 2Cl-(aq) + H2(g) + 2H20(l)

Net ionic equation:Zn(s) + 2H30+(aq) --> Zn2+(aq) + H2(g) + 2H20(l)

Acid-Base ReactionsNow we are going to use Bronsted-Lowry description to explore acid-base reactions.What was the Bronsted-Lowery theory?B-L acid donates protonsB-L base accepts protonsThe species that remains after a Bronsted-Lowry acid has given up a proton is the conjugate base of that acid.HF + H2O F- + H30+

Acid conjugate base

• A conjugate base is the species that remains after a Bronsted-Lowery acid has given up a proton.

• A conjugate acid is the species that forms when a Bronsted-Lowery base gains a proton.

The species that is formed when a Bronsted-Lowry base gains a proton is the conjugate acid of that base.

HF(aq) + H2O(l) F-(aq) + H30+(aq)

Base conjugate acid

HF(aq) + H2O(l) F-(aq) + H30+(aq)

Acid Base conjugate conjugate base acid

acid1 base2 base1 acid2

Conjugate pairs: (1)HF and F- (2)H20 and H30+

Strength of Conjugate Acids & Bases

• On Page 1 of your handout for this chapter, you have a table which lists and compares the strengths of various acids and their conjugate bases. Get your Ch. 14 handout out now.

Determining direction of equilibrium in Acid-Base reactions

The stronger an acid is, the weaker its conjugate base will be.

The stronger a base is, the weaker its conjugate acid will be.

From these concepts, we can predict the outcome of a reaction.

14.3 Assignments:489/1,2491/19-25492/26-30,36,37 (Overall practice problems)

Sample problem on next page:

492/23a: Identify the proton donor or acid and the proton acceptor or base. Label each acid-

base conjugate pair.CH3COOH + H20 H30+ + CH3COO-

acid base conjugate conjugate acid base

Another sample.

492/29a. Write the formula equation, the overall ionic equation, and the net ionic equation for a neutralization reaction that would form RbClO4.

Formula equation:RbOH(aq) + HClO4(aq) --> RbClO4(aq) + H20(l)

Overall Ionic equation:Rb+(aq) + OH-(aq) + H30+(aq) + ClO4

-(aq) -->

Rb+(aq) + ClO4-(aq) + 2H20(l)

Net ionic equation:H30+(aq) + OH-(aq) --> 2H20(l)

Amphoteric Compounds

These can act as either an acid or a base.Water acts as a base in this reaction:H2SO4(aq) + H20(l) --> H30+(aq) + HSO4

-(aq)

acid1 base2 acid2 base1

But, water acts as an acid here:NH3(g) + H20(l) NH4

+(aq) + OH-(aq)

Base1 acid2 acid1 base2

Neutralization Reaction

Acid + Base --> Salt + WaterHCl + NaOH --> NaCl + H20

H2SO4 + Ca(OH)2 --> CaSO4 + 2H20

Review

Acids BasesArrhenius concentration of: [H+] [OH-]Bronsted-Lowry H+ donor H+ acceptor Lewis, electron pair: acceptor donor