Complete question: what are the conditions for solubility in water, and is CH3NHCH3 soluble in water?

I will expand on the original question and explain the concept of solubility in general:
If you think about it, for any material in the world, there must be at least one chemical in which it dissolves in an ideal manner, and at any ratio that we choose, and that is… that chemical itself.
Water of course dissolves in water, soybean oil dissolves in soybean oil, paraffin in paraffin, mercury in mercury, and so on. This seems very obvious, but this fact gives rise to the concept of "like dissolves like", which means that if a material is best dissolved in itself, it would most likely dissolve in a similar material. The similarity refers to the chemical properties of the material – especially to the properties of the chemical bonds between the atoms.

Hence, metals dissolve in metals, polar compounds dissolve in polar solvents, non-polar compounds dissolve in non-polar solvents, hydrogen-bond-containing compounds dissolve in hydrogen-bond-containing solvents, and so forth. For example: common table salt (NaCl), which is an ionic/polar compound, dissolves in water, which is polar, but not in cooking oil, a non-polar compound. On the other hand, other types of oil are soluble in cooking oil, but water isn't.

In the process of producing aluminum, aluminum oxide (Al2O3, an ionic compound) is dissolved in molten cryolite (Na3AlF6, another ionic compound). Mercury, a metal that is liquid at room temperature, can dissolve copper and gold, other types of metals.

Mercury (adopted from Wikipedia)

Of course things are more complicated for molecules that form different types of bonds. For example, alcohols contain a polar region that forms hydrogen bonds (-OH) and a non-polar carbon backbone. Hence, the solubility of alcohols in water is determined by the length of the non-polar carbon backbone – the longer it is, the less soluble the alcohol. Drinking alcohol (ethanol) contains a short 2-carbon atom backbone, and therefore dissolves in water at any ratio. In contrast, panthenol (also known as pro-vitamin B5, an ingredient in many shampoos), contains a 5-carbon atom backbone chain and is thus only partially soluble in water, while alcohols with a longer, 20-carbon atom backbone, are hardly water soluble at all.

You specifically asked about the solubility of methylamine (CH3NHCH3(. This is a polar molecule that doesn't comntain any long carbon chains. The nitrogen-hydrogen group allows the formation of hydrogen bonds with water, so methylamine will dissolve quite well in water.

Dr. Avi Saig
Davidson Institute of Science Education
Weizmann Institute of Science

 

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2 comments

  • F you

    Five carbon backbone?

    I would like for you to display this five carbon backbone of pantin. Because your are undoubtedly and objectively incorrect with this statement which makes this entire document incorrect....

  • Ashutosh Bhakuni

    Hello

    Hello
    Can you tell me why water is called UNIVERSAL solvent and if it can be demonstrated to kids visually without much theory? I have read that it dissolves all salts and lots of substances, and is called so because it dissolves more substances than any other solvent. But it also doesnt dissolve a LOT of substances and isnt really universal that way...So if i tell a kid to test materials around the house and outside to see if they dissolve in water, then MOST of the materials dont dissolve and she/he might conclude that 'water dissolves some but it is certainly not UNIVERSAL solvent and most things dont dissolve in water'. The usual experiments where they try to 'show' this, actually use water, oil and alcohol with substance like salt, sugar, sand...in this case water will obviously dissolve salt and sugar more, but I feel that it isnt really honest or correct to make a huge leap from this activity and say water is a 'universal' solvent. So why is it called universal solvent? And how to really show its universal nature more concretely to a child? Will this require lab chemicals? Even then how to show it in lab? And does water dissolve 'every' material, even if in a microscopic amount, or are there some materials which just dont dissolve in water? Thanks!