AcidBase Reactions

1
Acid-Base Reactions

• Remember for our purposes an acid is a proton
  donor.
• a base is a proton acceptor usually OH-
• Review
• What is the net ionic equation for the
  reaction of HCl(aq) and KOH(aq)?
• Acid Base salt water
• H OH- H2O

2
Acid - Base Reactions

• Often called a neutralization reaction Because
  the acid neutralizes the base.
• Often titrate to determine concentrations.
• Solution of known concentration (titrant),
• is added to the unknown (analyte),
• until the equivalence point is reached where
  enough titrant has been added to neutralize it.

3
How to solve TitrationProblems

• Millimole (mmol) 1/1000 mol
• Molarity mmol/mL mol/L
• Makes calculations easier because we will rarely
  add Liters of solution.
• Adding a solution of known concentration until
  the substance being tested is consumed.
• This is called the equivalence point.
• Graph of pH vs. mL is a titration curve.

4
Titration Problem

• Where the indicator changes color is the
  endpoint.
• Not always at the equivalence point.
• A 50.00 mL sample of aqueous Ca(OH)2 requires
  34.66 mL of 0.0980 M Nitric acid for
  neutralization. What is Ca(OH)2 ?
• HELP
• of H x MA x VA of OH- x MB x VB

5
Acid-Base ReactionProblem

• Calculate the pH of 40.0 mL of 0.100 M HCl after
  the addition of
• a) 35 mL of 0.100 M NaOH
• b) 45mL of 0.100 M NaOH

6
Titration Curves
7

• Strong acid with strong Base
• Equivalence at pH 7

7
pH
mL of Base added
8

• Strong base with strong acid
• Equivalence at pH 7

7
pH
mL of Base added
9

• Weak acid with strong Base
• Equivalence at pH gt7

gt7
pH
mL of Base added
10

• Weak base with strong acid
• Equivalence at pH lt 7

lt7
pH
mL of Base added
11
Problem

• A student titrated 50.0 mL of 0.200 M HNO3 with
  0.100 M NaOH
• a) at what mL is of NaOH will the equivalence
  point be met?
• b) at the equivalence point, will the pH be
  lt7, gt7 or 7

12
Another Problem

• Titrate 50.0 mL of 0.10 M HF with
• 0.10 M NaOH
• a) at what mL is of NaOH will the equivalence
  point be met?
• b) at the equivalence point, will the pH be
  lt7, gt7 or 7

13
Indicators

• The approximate pH of a solution can be
  determined easily by using an acid-base indicator
• This is a substance which changes color in a
  specific pH range
• End point - when the indicator changes color.

14
Problems

• Calculate the pH of each of the following
  solutions
• 4.8 grams if lithium hydroxide in 250 mL of
  solution
• 0.93 grams of hydrogen chloride in 0.40 L of
  solution

15
More Problems ( yea!!)

• Calculate the pH of solutions prepared by
• Diluting 50 mL of 0.10 MHCl to a volume of 1.00 L
• Mixing 100 mL of 2.00x10-3 M HCl and 400 mL of
  1.0x10-3 MHClO4 ( assume the volumes are
  additive)