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Chapter 4

CHEM 14BL Chapter Notes - Chapter 4: Titration, Sulfuric Acid


Department
Chemistry and Biochemistry
Course Code
CHEM 14BL
Professor
Henary Maher
Chapter
4

Page:
of 3
1. Synthesis and Analysis of Aspirin
2. Russell, Arlene A. “A Study of A Weak Acid and Its Buffers (Part 1)” Chemistry Experiments
For Life Science Majors, Second Edition, pp. 43-45
3. The experiment focuses on synthesizing an organic compound known as Aspirin, or Acetyl
Salicylic Acid (ASA). Through the process of synthesizing salicylic acid and acetic
anhydride, these two compounds react to form aspirin. The techniques used in this
experiment are manipulative skills: analytical balance, volumetric pipet, volumetric solution,
titration, set up organic chemical reaction, purify via recrystallization, determine melting
point, and prepare calibration curve using Beer’s law. And the theoretical skills: calculate
percent yield, purity of compound from titration data, convert between absorbance and
transmittance, determine concentration from Beer’s law plot, interpret mass spectrum, and
determine purity from melting point of a compound.
4. Synthesis of Aspirin
oAdd ~150-mL of water in a 400-mL beaker
oAdd boiling chip + boil water on a hot plate
oHalf fill a 100-mL beaker with ice + add water to 50-mL mark
oWeigh 3 g of salicylic acid, then add to 125-ml flask
oIn a fume hood, add 5-mL of acetic anhydride + 5 drops H2SO4
oSwirl flask to wet the crystals + place flask in boiling water
oClamp neck of flask to ring stand + heat for 10 min
oRemove flask + add 10 mL of ice water (to decompose excess acetic anhydride)
oChill flask in ice until recrystallization is complete + stir occasionally
oAssemble vacuum filtration
oPour liquid into funnel, leaving crystalline aspirin in flask
oAdd 10-mL ice water to flask + swirl + pour into funnel with aspirin
oUse spatula to scrape rest of the aspirin into the funnel
oAdd 5-mL of ice water to flask to wash residue into funnel
oLeave suction on to draw air through the funnel + “dry” aspirin for 5 min
oRelease vacuum by removing tubing from filter flask
oNote: Don’t turn off water (waste water will go into flask)
oScrape aspirin into a pre-weighted watch glass
oRecord weight of watch glass + crude product (to determine yield of product)
Recrystallization of Crude Aspirin
oTransfer crude product to 125-mL flask
oSwirl flask + add drops of ethanol (8-10 mL) to dissolve crude product
oPlace boiling stick in flask + boil on hot plate + turn off
oSlowly add water (<25 mL) from dropper until solid forms
oTurn on hot plate + add few drops of ethanol until solid redissolves
oRemove flask from hot plate + stopper it + let it cool
5. Salicylic Acid (Reagent Grade)
a) Salicylic Acid
b) C7H603
c) 138.12 g/mol
d) mp: 158-161C bp: 211C density: 1.440 g/cm^3
e) It is harmful if swallowed and it can cause mild irritation with skin contact. It can also
cause serious eye damage. Severe over-exposure can result in death.
f) If spilled, avoid breathing vapors, mist or gas. The spill area should be ventilated and it
should not be disposed down the drain. It should be cleaned up in a way that does not
create dust. It should be disposed by an approved waste disposal plant.
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6. Sulfuric Acid (concentrated)
a) Sulfuric Acid
b) H2SO4
c) 98.08 g/mol
d) mp: -35-10.36C bp: 270-340C density: 1.84 g/cm^3
e) It can cause severe skin and eye damage. It is harmful if swallowed. It is toxic to aquatic
life
f) If spilled, avoid inhalation. The spillage should be diluted with water and soaked up with
an absorbent material. It should be disposed by an approved waste disposal plant. If
necessary, the spill area can be neutralized with a dilute sodium carbonate solution.
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7. Acetic Anhydride (Reagent Grade)
a) Acetic Anhydride
b) C4H6O3
c) 102.09 g/mol
d) mp: -73C bp: 138-140C density: 1.08 g/mL
e) It is extremely hazardous. It is harmful if swallowed or with skin contact. It is toxic if
inhaled. It is vapor flammable.
f) If spilled, avoid inhalation. Wear proper protective equipment and respirator. Remove
from sources of flame to prevent fumes from spreading. The spillage should be cleaned
up using a vacuum cleaner. It should be disposed by an approved waste disposal.
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