I-Acids and Bases

Prem SattsangiCopyright 2008

#2 Introduction to Acids and Bases Chapter - 8

• 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

• Waste Beaker 50 mL.• 24 well tray with solutions.• 12 well tray• Microstirrer• Distilled water bottle.

#4 Stock Solutions

• 2.00M HCl 0.1M NaOH• 0.10M HCl ~1M NaOH• BTB

• 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 Y Y B B• 0.1M NaOH 1 2 3 4 5 6 7 8 9 10 11 12• 0.1M HCl 5 5 5 5 5 5 5 5 5 5 5 5• BTB 1 1 1 1 1 1 1 1 1 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]

• 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 =*10.5646After transfer• Weight of empty tray. = *0.5161g• Egg shell wt. =*10.5646 - *0.5161Difference in weights: = 0.0485g

#14 Reaction: Egg shell + HCl

• 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.