section 16.3 titrations and buffers 1.to know how to neutralize acids and bases (titration) learning...
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Section 16.3
Titrations and Buffers
1. To know how to neutralize acids and bases (titration)
Learning Goal
Section 16.3
Titrations and Buffers
Remember that… (add this to your notes)
Acid + Base Water + Salt
Ex.: HCl + NaOH H2O + NaCl
Acid-Base Reactions (review)
This is a double replacement reaction
Notice that H+ and OH- H2O
This is a neutralization reaction
Section 16.3
Titrations and Buffers
Acid-Base Titrations
Titration – delivering a measured volume of a solution of known concentration into a solution being analyzed determine the concentration of the solution (analyte)
We need to neutralize the solution, therefore…
What should you add to an acid to neutralize it?
What should you add to a base to neutralize it?
BASE
ACID
Section 16.3
Titrations and Buffers
Titrant (standard solution)
Analyte (solution being analyzed)
The titration is
stopped when the
pH = 7
↓
Buret – device used for accurate
measurement of the delivery of a liquid
Stoichiometric point
(equivalence point) –
when just enough titrant
has been added to react
with all of the solution
being analyzed
A pH indicator is added to the analyte so the color changes when the pH
reaches 7(or a pH meter could be used)
How will we know when the
solution has been
neutralized?
Section 16.3
Titrations and Buffers
Acid-Base Titrations
• Titration curve (pH curve) – plot of the data (pH vs volume) for a titration
pH changes quickly
close to the equivalence
point.
Section 16.3
Titrations and Buffers
Calculating the Volume of Titrant Needed in Acid-Base Titrations (using M=n/L)
How much 0.100 M NaOH is needed to titrate 50.0 mL of 0.200 M HNO3?
1. Calculate how many moles of H+ are in the analyte.
0.0500 L HNO3 x 0.200 mol H+ = 1.00 x 10-2 mol H+
1L
2. Calculate the volume of titrant solution that contains the needed number of moles of OH- (same as moles of H+).
V = n/M = 1.00 x 10-2 mol OH- = 1.00 x 10-1 L
0.100 mol/L or 100. mL
Section 16.3
Titrations and Buffers
Calculating Molarities and Volumes in Titrations (using one formula) Remember that Molarity x Volume (L) = n• Moles of H+ must equal moles of OH- for neutralization• Since the acid or base may give off more than one H+ or
OH-, we must use the mole ratio of base/acid:
MaVa (b/a) = MbVb
Ex.: H2SO4 + 2NaOH 2H2O + Na2SO4
Notice that this is a double displacement/replacement reaction.
In most neutralization reactions: acid + base water + salt
Section 16.3
Titrations and Buffers
To understand how the pH in a solution (eg. Blood) is kept constant when acid or base are added (buffers)
Learning Goal
Section 16.3
Titrations and Buffers
B. Buffered Solutions
• Buffered solution – resists a change in its pH when either and acid or a base has been added– Presence of a weak acid and its conjugate base
buffers the solution:
Buffer = weak acid + salt containing conj. base of acid
Section 16.3
Titrations and Buffers
B. Buffered Solutions
Section 16.3
Titrations and Buffers
Example of buffered solution:
HC2H3O2, NaC2H3O2
weak acid salt that contains conjugate base of acid
(C2H3O2-)
• If strong acid is added to the solution, the H+ ions react with the conjugate base and form the weak acid:
Net reaction: H+ + C2H3O2- HC2H3O2
• If strong base is added to the solution, the OH- ions extract the protons from the weak acid to form water:
Net reaction: OH- + HC2H3O2 H2O + C2H3O2-