Transcript Titrations - TeacherWeb

Drill – 5/17/11
1. Calculate the pH of an aqueous
solution that contains 5.00 g of
HNO3 in 2.00 L of solution.
2. What would the pOH be?
Titrations
Acid-base indicators are…
• Compounds whose color is sensitive to
pH.
• Indicators are either weak acids or weak
bases.
• For example, weak acid indicators will lose
a proton in a base. The deprotonated
version displays a different color.
Measuring pH
• pH paper is a universal indicator. It is
made by soaking the paper in several
different indicators.
• A pH meter measures the voltage between
two electrodes. The voltage is measured
based on the concentration of the
hydronium ion.
Phenolphthalein
• An indicator that changes color from clear
in acid to pink in base (pH 8-10).
• This is the indicator that we will use in the
lab tomorrow!
Titrations
• The controlled addition and measurement
of the amount of a solution of known
concentration required to react completely
with a measured amount of a solution of
unknown concentration.
Standard Solution
• The solution that contains the precisely
known concentration of a solute is known
as a standard solution. The standard
solution is often the titrant (it is titrated into
the unknown solution)
• http://www.dartmouth.edu/~chemlab/techni
ques/buret.html
• Pg 518-519
Good color!
Too much base!
Titration Curve
• A titration curve is
drawn by plotting
data attained during
a titration, titrant
volume on the x-axis
and pH on the y-axis.
The titration curve
serves to profile the
unknown solution.
Equivalence Point
• The point at which the two solutions used in
a titration are present in equal amounts
(same number of moles of acid and base)
Amount of acid in moles = Amount of base in moles
*Note: this is not the same volume or the same
concentration, just the same MOLES
Equivalence Point
• Strong acid + strong base =
equivalence point at pH of 7
• Strong acid + weak base =
equivalence point at pH of <7
• Weak acid + strong base =
equivalence point at pH of >7
• If we know the molarity and the volume of
acid used, then can we calculate the
amount of moles of acid? How?
• MolA = MAVA
How to solve titration problems:
1. Write the balanced neutralization equation
2. Solve for moles of given (using molarity and
volume)
3. Convert from moles of given to moles of
unknown using mole ratio
4. Use moles of unknown to solve for molarity
or volume.
•
If moles are equivalent, then: MAVA =MBVB
• Worksheet!
• Green workbook, pg. 272 -275