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Water-Solubilities of Organic Compounds
In this exercise, you will be determining the solubilities of different organic
compounds in water. You will vary three factors: the functional group, the size,
and the shape of the organic compound. From this exercise, you should learn
which functional groups enhance water-solubility, and how the size and shape of
the organic compound influences water-solubility. You will be determining the
amount of water needed to dissolve 0.5 mL of different organic compounds. If a
compound doesn't dissolve to the extent of 0.5 mL in 20 mL of water, we will
arbitrarily call that compound "insoluble". The solubilities can be explained by
examining how well each compound can hydrogen bond with water. The overall
polarity of each molecule must be considered, as well as its size and shape.
Molecular weights, not just numbers of carbons, must be compared.
General Experimental Procedure for Determining Water-Solubility
Obtain 0.5 mL of the organic compound (the bottles of organic compounds have
droppers attached with a mark at the 0.5 mL mark), and place it in a large test-tube.
Add 2 mL of water to the test-tube, cork it, and shake it gently. Observe whether
the organic compound dissolved. If it has dissolved, you are finished with that
organic compound. If it has not dissolved, add an additional 2 mL of water, and
gently shake. Continue adding water 2 mL at a time until the organic compound
dissolves, or until you have added a total of 20 mL of water. Report the minimum
number of mL of water required to dissolve each organic compound, or
"insoluble", if it doesn't dissolve in 20 mL.
Waste Disposal
Water-soluble compounds may be flushed down the sink with a large amount of
water. The contents of the test-tubes containing water-insoluble compounds should
be placed in the large beaker in the hood marked "Water-Insoluble Waste".
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Compounds to test:
Compound
Number
1
2
3
4
5
6
7
8
9
10
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Compound Name
Chemical Structure
Methanol
Ethanol
1-Propanol
1-Butanol
1-Pentanol
1-Hexanol
Pentane
1,4-Butanediol
Diethyl ether
Pentanal
Diethylamine
CH3OH
CH3CH2OH
CH3CH2CH2OH
CH3CH2CH2CH2OH
CH3CH2CH2CH2CH2OH
CH3CH2CH2CH2CH2CH2OH
CH3CH2CH2CH2CH3
HO-CH2CH2CH2CH2OH
CH3CH2OCH2CH3
CH3CH2CH2CH2CH=O
CH3CH2NHCH2CH3
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CH234 Water-Solubility Lab
Name: ________________________
Water-Solubility Data
Compound Compound Name
Number
1
2
3
4
5
6
7
8
9
10
11
Volume of water needed to
dissolve 0.5 mL of compound
Methanol
Ethanol
1-Propanol
1-Butanol
1-Pentanol
1-Hexanol
Pentane
1,4-Butanediol
Diethyl ether
Pentanal
Diethylamine
If a compound didn't dissolve in 20 mL of water, put ">20 mL".
Answer the following questions
1. On a separate page, draw structures showing how water can hydrogen-bond
with each compound, if it can. If it can't, say it can't. For compounds 1-6,
you can just draw one generic “R-O-H”, rather than drawing all 6 alcohols.
2. What was the order of solubilities of the alcohols, compounds 1-6? Explain
why this order was observed.
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3. What the order of solubilities of compounds 1-pentanol, 1,4-butanediol, and
pentanal? Explain why this order was observed.
4. What the order of solubilities of compounds 1-butanol, pentane, and diethyl
ether? Explain why this order was observed. How water-soluble is
diethylamine compared to these?
5. 1-butanol and diethyl ether (CH3CH2OCH2CH3) have identical molecular
formulas, but 1-butanol has a much higher boiling point than diethyl ether.
Explain why on the molecular level.