How to test if some unknowns are covalent or ionic?

[Infinity]

So...how do you carry out an experiment to test if these unknowns are covalent (polar or non-polar) or ionic?

 

Unknowns:

C6H12O6 --NaCl --CH4N20 --C6H8O7

[jdurg]

Dissolve it in water, then put a current through the solution. If it dissolves and conducts electricity, then it's ionic. If it dissolves and does NOT conduct electricity, it is covalent. If it doesn't dissolve in water, then try and dissolve it in some xylene. If it dissolves, it's covalent. That should cover all of the substances you have listed there.

[Ferdinand]

So, "Acids are ionic!!!!!"

[jdurg]

Organic acids are a PERFECT example of why you can't really say something is 100% ionic or something is 100% covalent. Numerous organic acids are VERY ionic in character while still being considered a covalent compound. A good analogy is to say that there are two types of temperatures; hot and cold. In reality, there are many subtle layers in between.

 

In the example the original poster gave, the tests I described would easily tell the difference between the substances listed there.

[woelen]

Organic acids are a PERFECT example of why you can't really say something is 100% ionic or something is 100% covalent. Numerous organic acids are VERY ionic in character while still being considered a covalent compound. A good analogy is to say that there are two types of temperatures; hot and cold. In reality' date=' there are many subtle layers in between.

 

In the example the original poster gave, the tests I described would easily tell the difference between the substances listed there.[/quote']

In fact, acids (also inorganic ones) are purely covalent compounds, such as HCl, H2SO4, CH3COOH, but when they are dissolved in water, an hydrogen ion (proton) can be split off easily and that is solvated by the water:

 

HCl + nH2O --> [H.nH2O](+) + Cl(-)

 

Most times this is simplified somewhat as follows:

 

HCl + H2O --> H3O(+) + Cl(-)

 

So, the compound itself is covalent, but when it dissolves in water, a chemical reaction occurs with the water, such that a new compound is formed, which is ionic. For many acids, this reaction also is noticeable very well. Dissolving HCl gas in water, or adding pure H2SO4 or HNO3 to water results in formation of a LOT of heat, indicating that a real (exothermic) chemical reaction occurs. I once did an experiment where accidently some HCl gas was streaming along one of my fingers. Initially I did not notice, until I felt that my finger became very hot, due to reaction of HCl gas with humidity from the skin . Quite strange feeling to have a gas react with the water from your skin and you feeling the heat of that reaction.

 

This is a large difference with real ionic compounds, such as NaCl. In the latter, the solid also contains Na(+) and Cl(-) ions. This is absolutely not the case for HCl, nor for H2SO4, CH3COOH and other acids.

 

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Another thing to point out, is that many compounds can be purely ionic and purely covalent at the same time.

 

An example is NaNO3. The solid also is purely ionic, it contains Na(+) ions and NO3(-) ions. The NO3(-) ion, however, is purely covalent. It can be regarded as a covalent molecule, with a charge. When dissolved, it does not break down further in smaller ionic parts.

 

 

Dissolve it in water, then put a current through the solution. If it dissolves and conducts electricity, then it's ionic. If it dissolves and does NOT conduct electricity, it is covalent. If it doesn't dissolve in water, then try and dissolve it in some xylene. If it dissolves, it's covalent. That should cover all[/b'] of the substances you have listed there.

Your test covers all the compounds mentioned above, but in general I would say many, or most, not all.

 

If a compound does not dissolve in xylene, nor in water, then the test is not conclusive. In that case, the compound can be either ionic, covalent or something in between. Covalent example: Polymeric compounds (e.g. plastics). Ionic example: CaF2.

[Infinity]

Hi, but how do you make an quantitative experiment to test that? Also, how about the polar and non-polar stuff? it seems harder to test whether a covalent compound is polar or not.