What did one titration tell the other Lets meet at the endpoint Why are chemists great for solving problems They have all the solutions Titration A lab procedure by which the concentration of acidic or alkaline solutions are examined and determined ID: 423744
Download Presentation The PPT/PDF document "TITRATIONS" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
TITRATIONSSlide2
What did one titration tell the other?
Let's meet at the endpoint.
Why are chemists great for solving problems?
They have all the solutionsSlide3
Titration
A lab procedure by which the concentration of acidic or alkaline solutions are examined and determinedSlide4
A strong acid titrated with a strong base will result in neutralization around pH 7Slide5
More complex titrations involve weak acids (or bases) titrated with strong base (or acid) and
polyprotic
acidsSlide6Slide7
pH curves
Graphs that show continuous changes in pH as the
titrant
is added to the sampleSlide8
The curves are drawn using the amount of
titrant
added as the x-axis and the pH as the y-axisSlide9
The
midpoint of a nearly vertical portion of the line
is known as the
equivalence pointSlide10
The number of equivalence points in a pH graph indicates the molar ratio between the acid and the base involved in the titrationSlide11
There will be
1 equivalence point
for
each complete proton transfer
that occursSlide12Slide13
Example 1
Sketch the pH curves in a titration graph, demonstrating the change in pH when a weak acid is titrated with a strong base. In this case use CH3COOH titrated with
NaOHSlide14
Because CH3COOH is a weak acid it acts as a buffer and does not give up its H+ as easily.
The pH at the endpoint is therefore slightly higher because more strong base is required. Slide15
Example 2
Sketch
th
pH diagram of a
polyprotic
base Na2CO3, titrated with a strong acid
HCl
. Use 25mL of 0.20mol/L Na2CO3 titrated with 0.20mol/L
HCl
for your data. Slide16
Example 3
Sketch the pH graph of the titration of
polyprotic
acid H3PO4 titrated with a strong base
NaOH
. In terms of experimental data, use 25mL of 0.12mol/L H3PO4 titrated with 0.12mol/L
NaOH
.Slide17
INDICATORSSlide18
An indicator is a solution that changes color to signal that the equivalence point has been reached. Slide19
The point at which an indicator changes color is called its transition point.
Try to get the transition point near the equivalence pointSlide20
Choosing an Indicator
Look at the curve to find the equivalence point
From the indicator list, choose an indicator with a range near the equivalence pointSlide21
Acid-base indicators are a conjugate weak acid-weak base pair that have distinctly different colors when dissolved in water
Indicators are larger molecules (big enough to be noticed)Slide22
Example 6
A student finds that an unknown solution is colorless when mixed with phenolphthalein, red when mixed with
chlorophenol
red, and blue when in the presence of
bromocresol
green. She hypothesizes that the pH of the solution is 7.5. Do the indicators provide evidence to support her hypothesis?