Acids and Bases

Chapters 15

I. Introduction A. Characteristics of acids 1) formulas BEGIN with Hydrogen 2) taste sour 3) turn blue litmus paper to RED 4) react with and neutralize bases

B. Characteristics of Bases 1) formulas typically END with OH 2) taste bitter 3) feel slippery 4) turn red litmus paper BLUE 5) react with and neutralize acids

I. Review of Acid Nomenclature A. Binary acids

hydro + (root) +ic acid ex: HCl - hydrochloric acid HI - hydroiodic acid

B. Polyatomic acids (a.k.a oxyacids)

1) polyatomic ions ending with -ATE (root) + ic acid

ex: H2SO4 - sulfuric acid HClO3 - chloric acid

2) polyatomic ions ending with -ITE (root) + ous acid

ex:HNO2 - nitrous acid

Practice Nomenclature a) HClO2

b) H2S

c) HIO4

d) HBrO

e) HMnO4

f) H2CrO4

g) HOH

II. Conjugate Acid and Base Theory A. Behaving like an Acid means to GIVE AWAY a H-atom

B. Behaving like a Base means to ACCEPT an H-atom

C. Ionization reactions always involve acid/base pairs:

ex: HCN + H2O <-----> CN - + H3O + acid conj. acid base conj. base

ex: NH3 + H2O <------> NH4+ + OH -

base conj. acidacid conj. base

amphoteric - able to act as either acid or base

Do Now1) Indicate the conjugate base of H2S

2) Indicate the conjugate acid of HSO4-

3) Indicate the conjugate base of HPO4-2

4) Indicate the conjugate acid of HCO3-

notes: 1) acids lose H to become a conjugate base 2) bases accept H to become a conjugate acid 3) WEAK “originals” make STRONG conjugates 4) STRONG “originals” make WEAK conjugates

ex: HCN + H2O <-----> CN - + H3O +

weak strongweak strong

ex: NH3 + H2O <------> NH4+ + OH -

weak weak strong strong

notes: 1) H3O + is always a STRONG ACID

2) OH - is always a STRONG BASE

Strengths of AcidsI.Binary acids A. Within a group … 1) the weaker the bond the stronger the acid 2) weaker bonds occur with larger anions

B. Within a period1) the more electronegative anion the stronger the acid

ex: Arrange this from weaker (1) to stronger

HI HF HCl HBr

Strengths of AcidsII. Oxyacids A. With the same # of oxygens… - more electronegative center = stronger

B. Same atoms, more oxygens- the more oxygen there are = stronger the acid

HClO HClO2 HClO3 HClO4

HClO HBrO HIO

III. Strengths of Acids and Bases A. Strong acids HCl

HBr

HI

HNO3

HClO3

HClO4

H2SO4

B . Strong bases (Group IA) - OH (Group IIA) - OH

Weak acids

all the others

Weak bases

NH3 covalent compounds with C, H, N in the formulas

ex: HF CH3NH2 Ca(OH)2 HNO2 Na2CO3

IV. Acid - Base Theories

A. Three prevailing theories exist to define acids/bases

1) Arrhenius - acids = H in formula - bases = OH in formula ex: HCl LiOH

2) Bronsted - Lowry - acids = proton donor - bases = proton acceptor ex: HCl NH3

3) Lewis - acids = electron pair acceptor - bases = electron pair donor ex: BF3 NH3

DO NOW

H2O + HC2H3O2 => H3O+ + C2H3O2-

Identify the acid/bases and conjugate acid bases and then

identify as weak or strong.

ex: HCN + H2O <-----> CN - + H3O +

ex: NH3 + H2O <------> NH4+ + OH -

Bronsted acids: Bronsted bases

V. The pH Scale A. Concentrations of H+ and OH- are often converted to a more convenient mathematical form:

1) pH = - log [H+]ex: instead of [H+] = 1.00 x10 -6 M . . . . . . . . pH = 6.000

How? pH = - log (1.0 x 10 -6) = 6.00

2) pOH = - log [OH-]

ex: instead of [OH-] = 2.0 x10 -3 M . . . . . . . . pOH = 2.70How? pOH = -log (2.0 x10 -3 ) = 2.70

B. The ionization of water causes the product of [H+] and [OH-] to always equal a constant:

1) [H+] [OH-] = 1.0 x 10 -14 (known as Kw)

2) If the concentration of one is known, the other can be calculated

Ex: [H+] = 1.00 x 10-4 M . . . . . .

[OH-1] = 1.00 x 10-10 M

OR . . . . . . If pH = 4, then pOH = ?????

pOH = 10

Practice:

1) What is the pH of 2.50 x 10-3 M HCl?

2) What is the pOH of 3.5 x 10-8 M HNO3?

3) What is the [H+] of a solution with pH = 9.20?

4) What is the [OH-] of a solution with pH = 6.85?

C. Acidic/Basic solutions are determined by their pH values:

1) pH < 7 . . . . . . . acidic

2) pH > 7 . . . . . . . basic

3) pH = 7 . . . . . . . neutral

pH Chart Showing Common Substances

Try It Now

Write the reaction that occurs when NaOH is added to

HCl.

VI. Acid-Base Titrations

A.An acid and a base react to form:

NaOH + HCl NaCl + H2O base + acid salt + water

B. Neutralization

1) occurs when an acid and a base react

2) same as double replacement reaction

C. A solution is neutral when moles acid = moles base

Ex: Suppose 42.00 mL of a 0.150 M NaOH solution is required to neutralize 50.00 mL of an unknown HCl solution. What is the molarity of the HCl solution?

Answer: 0.126 M HCl

Ex: Suppose 42.00 mL of a 0.150 M NaOH solution is required to neutralize 50.00 mL of an unknown H2SO4 solution.

What is the molarity of the H2SO4 solution?

Answer: 0.0630 M H2SO4

Ex: If 50.00 mL of a 0.2000 M HCl solution is titrated with 0.1500 M NaOH…. a)What is the pH before any NaOH has been added?

b)What is the pH after 10.00 mL of base has been added?

a)What is the pH after 70.00 mL of base have been added?

Review

1) List 3 characteristics of acids and bases

2) What is the conjugate base of OH- ?

3) What is the [OH-] of 2.5 x 10-8 M HCl?

4) Write the formula for hydroiodic acid.

5) Identify NH3 as Arrhenius acid/base, Bronsted

acid/base, or Lewis acid/base

Review

6) What is the pH of 3.0 x 10-4 M NaOH?

7) What is the pH after 5.0 mL of 0.20 M HCl is

titrated with 8.0 mL of 0.10M NaOH?

8) How many mL’s of 0.250 M NaOH are required

to neutralize 30 mL of 0.15M HCl?

9) Which acid is strongest … HIO or HIO3

10) Which base is strongest … Cl- or F- ?