Transcript I-Acids and Bases - Personal.psu.edu

I-Acids and Bases
Prem Sattsangi
Copyright 2008
#2 Introduction to Acids and
Bases Chapter - 8
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Individual work
Section A Facts and Questions.
Section C Acid-base titration.
M of Unknown HCl U.K.#_____.
Section D Calibration of
microburet.
• Section E Analysis of the egg
shell.
#3 Getting Ready
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Waste Beaker 50 mL.
24 well tray with solutions.
12 well tray
Microstirrer
Distilled water bottle.
#4 Stock Solutions
• 2.00M HCl
• 0.10M HCl
• BTB
0.1M NaOH
~1M NaOH
• Crushed Egg shell
• 95% Ethanol
#5 Acid-Base Titration
• Equivalence point = The first blue well
• Add 1 drop NaOH to well #1, stir, wipe the
stirrer clean…
• SERIAL TITRATION: #Drs NaOH = well#
• Color
YY
B B
• 0.1M NaOH
1 2 3 4 5 6 7 8 9 10 11 12
• 0.1M HCl
555555555 5 5 5
• BTB
111111111 1 1 1
• Well#
1 2 3 4 5 6 7 8 9 10 11 12
#6 Serial titration 0.1 M HCl
Steps
4
3
2
1
#7 Calculation (drs. In place of mL)
• NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l)
• ______ drops X 0.1 M NaOH
• = 5 Drops X 0.1 M HCl
• Discuss with teacher if:
• Your end point is not in the fifth well.
#8 Calibration of the Micropipet
[Uniform Size Drops]
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Fill MP with DW,
Hold vertical ~1” from the tray.
Squeeze gently 1 drop.
Record weight up to 0.0000g.
Tare the balance.
Repeat, record 10 readings.
Discard the readings that are too much off.
You MUST have 10 good readings.
#9 Calculation of Mean and
Standard Deviation
• Use TI 30 to calculate Mean and Std. Dev.
• E.g. if the date is 9, 4, 4, 5,
• Mean = 5.5
Std. Dev. = 2.38….
• Enter the data as follows.
9, +, 4, +, 4, +, 5, +,
Mean: 2nd xn-1 = 2.38; Std.D. 2nd X(bar)
• Write ST.#, Wt of 1 drop (g) on the pipet.
• Apply a tape over it.
#10 Getting Ready for U.K.
• U.K.#___ Check. It should correspond
to your station #.
• M ranges from 0.2 to 0.4 M.
• 12 well tray
• 2 drs U.K. + 1 dr BTB
• 24 well tray
• 20 drs U.K. + 2 drs BTB
• 20 drs U.K. + 2 drs BTB
#11 Titration of U.K.
• Empty the U.K. micropipet in its
well.
• Wash 2-3 times with DW.
• Rinse 2-3 times with 0.1 M NaOH.
• Fill ~half way with 0.1 M NaOH.
• Titrate: Keep micro stirrer in tray till
the end point is reached.
#12 Weighing of the Egg Shell
(Balance drifts)
• Check balance reading, 0.0000
• TARE if needed
• Weigh a plastic tray on Analytical
balance.
• Add slightly less than a level spoon.
• (~0.05 g egg shell)
• Record weight up to 4 decimal
places.
#13 Weighing Observations
OBSERVATIONS:
Weight
Wt of Plastic Tray
= 0.5153g
• Wt of Tray + egg shell =*10.5646
After transfer
• Weight of empty tray. = *0.5161g
• Egg shell wt.
=*10.5646 - *0.5161
Difference in weights:
= 0.0485g
#14 Reaction: Egg shell + HCl
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Running the reaction:
CaCO3 + 2HCl  CaCl2 + H2O + CO2
[1 mol CaCO3 reacts with 2 mol HCl]
Add 1-2 drops of 95% ethanol to egg
shell.
• Use calibrated micropipet to add 30
drs of 2.00 M HCl in the well with
egg shell.
#15 Caution: Hot Water
• Hold pipet with a folded paper towel.
• Take ~1 cm hot water 2-3 times to
condition the glass pipet.
• Add hot water in adjoining well.
• Leave a microstirrer in the well and stir
every other minute.
• Allow the reaction to proceed (~10-15
minutes).
#16. Result Reporting
• Molar concentration of NaOH is
to be copied from the Board.
• Calculate the result carefully.
• Check before submitting.