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I have been given a substance which is unknown in my class. The substance is white in colour and is in a powder form. I have conducted a few tests and have found out that the substance is a covalent compound.

Properties of the substance

  • Has a low melting point. When the item was melting it left a yellow/orange colour liquid, later it hardened and retained the same yellow/orange colour.
  • Soluble in water
  • Does not conduct electricity in solid state
  • Does not conduct electricity when dissolved in water
  • pH of 3-4
  • Soluble in Ethanol
  • Is not a sugar, used bennedict's solution and did not turn red instead gave of vapour and started bubbling.

From these steps I have concluded that the substance is a covalent compound. However, I need to find exactly what type of elements is in the covalent compound. If you could suggest a test to conduct to figure out what type of elements there are, it would be very helpful. Thanks.

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    $\begingroup$ Is the aqueous solution of it acidic, alkaline or neutral? $\endgroup$ – Waylander Nov 26 '20 at 8:21
  • $\begingroup$ I have not tested the PH level yet but if that helps, I will try it out. If the aqueous is acidic then the substance will be acidic, am I correct? $\endgroup$ – Shack Nov 26 '20 at 8:26
  • $\begingroup$ Is it soluble in ethanol ? in an alcane like gasoline, cyclohexane, petroleum ? $\endgroup$ – Maurice Nov 26 '20 at 9:00
  • $\begingroup$ I have only tested the solubility in Water, if ethanol helps, I will try that out too. $\endgroup$ – Shack Nov 26 '20 at 9:03
  • $\begingroup$ Also how would ethanol help in this situation? $\endgroup$ – Shack Nov 26 '20 at 9:10
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The problem is huge, because there exist many millions of different compounds which are white, soluble in water, and do not conduct electricity. Here are a couple of preliminary tests.

You might first determine if it is organic, by heating it in a test tube in a Bunsen burner. It will darken and be progressively transformed into charcoal if it is organic. Is it soluble in ethanol ? Is it soluble in an alcane like gasoline, cyclohexane, petroleum ?

Does it react with a diluted solution of CuSO4 ? If it produces a deeper blue color, it is probably some amine like RNH2, or a complexant agent like tartaric acid. If it produces a colored precipitate (blue or green), it may be a basic substance or a carboxylic salt.

Does it discolor Bromine water ? If yes, it probably contains a double bond C=C.

Does it react with Fehling's reactant (solution of CuSO4 plus much sodium tartrate and a few NaOH) ? If it does make an orange or brown precipitate at boiling temperature, it is a reducing sugar.

Does it react with diluted solution of permanganate KMnO4 ? Try in acidic and in basic solution. If so there is a reducing agent, and further study must be done.

Does it react with Tollens' reagent (solution of silver nitrate plus ammonia) producing a silver mirror at boiling temperature ? If yes, it is an aldehyde.

Knowing if the substance contains nitrogen is a little bit more difficult, as you should do Lassaigne test : heat it with a little bit metallic sodium in a test tube to high temperature, then dissolving into water with iron compounds. This a bit more dangerous : It requires some skill

There are plenty of other tests that could be made. Solving this problem in a general way would take hours. It is nearly impossible to solve it now. Try to find a treatise of organic qualitative analysis.

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  • $\begingroup$ My substance is soluble in ethanol, does this mean its organic? $\endgroup$ – Shack Nov 27 '20 at 6:37
  • $\begingroup$ Also, I have burnt the compound in a test tube in a bunsen burner yet the substance is not darkening and it dissolves in Ethanol. When it was burning it also released gas whihc could be smoke or vapor. $\endgroup$ – Shack Nov 27 '20 at 7:32
  • $\begingroup$ Does it react with solutions of CuSO4, or with AgNO3, or with KMnO4 ? Try ! Does it color the flame ? $\endgroup$ – Maurice Nov 27 '20 at 10:26

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