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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".

Compounds to test:

Compound Number

/ Compound Name / Chemical Structure
1 / Methanol / CH3OH
2 / Ethanol / CH3CH2OH
3 / 1-Propanol / CH3CH2CH2OH
4 / 1-Butanol / CH3CH2CH2CH2OH
5 / 1-Pentanol / CH3CH2CH2CH2CH2OH
6 / 1-Hexanol / CH3CH2CH2CH2CH2CH2OH
7 / Pentane / CH3CH2CH2CH2CH3
8 / 1,4-Butanediol / HO-CH2CH2CH2CH2OH
9 / Diethyl ether / CH3CH2OCH2CH3
10 / Pentanal / CH3CH2CH2CH2CH=O
11 / Diethylamine / CH3CH2NHCH2CH3

CH234 Water-Solubility LabName: ______

Water-Solubility Data

Compound Number

/ Compound Name / Volume of water needed to dissolve 0.5 mL of compound
1 /

Methanol

2 / Ethanol
3 / 1-Propanol
4 / 1-Butanol
5 / 1-Pentanol
6 / 1-Hexanol
7 / Pentane
8 / 1,4-Butanediol
9 / Diethyl ether
10 / Pentanal
11 / 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.
  1. What was the order of solubilities of the alcohols, compounds 1-6? Explain why this order was observed.
  1. What the order of solubilities of compounds 1-pentanol, 1,4-butanediol, and pentanal? Explain why this order was observed.
  1. 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?
  1. 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.