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Alcohols and solubility

  1. Oct 31, 2004 #1
    hi. im in grade11 chemistry and have a few questions regarding alcohols and solubility in water (polar/non-polar molecules).

    1) how does the OH groups in surcrose and glycerin help them to be water soluble?

    2) what would you use to clean your hands and the paint brush after painting with latex paint? explain.

    3) what solvent would you use to clean your hands and the paintbrush after painting with enamel(alkyd) paint? explain

    if you could help me thatd be great! thanks=D
  2. jcsd
  3. Oct 31, 2004 #2


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    equivalent dissolves equivalent

    1. Alcohols like sucrose and glycerin are soluble in water, since O-H groups can be dissociated in aqueous solution to give O- H+ ions, and they can easily hydrated (dissolved).
    2. As mentioned in this website, latex paints are water-soluble; this means that you can use warm water (for quick removal) to clean your hands and the paint brush after finishing your work.
    3. This website tells that alkyd paints are oil-based; so treatment with an organic solvent, preferably 1,1,1-trichloroethylene, would be good. There are commercial products known as "thinner" for this purpose.

    We can conclude that the famous sentence "equivalent dissolves equivalent" can be applied to your questions.
  4. Oct 31, 2004 #3
    i have one question though, what makes surcrose and glycerin different from butanol and pentanol that allows them to be soluble in water, and not the mentioned alcohols.

    also, what makes ethanol and butanol different ? (ethanol is water soluble, but not butanol). i speculate this has something to do with the hydrocrabon chain, but is the hydrocarbon chain polar or non-polar? and if so, how does it affect its solubility in water? thanks.
  5. Nov 1, 2004 #4
    In addition to what chem_tr said there is an important effect operative in polar solvents: that of intermolecular hydrogen bonding (also called H-bonding). If a compound contains a hydrogen bonded to an electronegative atom such as O, F or N, then it can in principle participate in weak attractive interactions with electronegative atoms such as O, F, N.

    The hydrogen bond causes weak attractive forces to develop between molecules of the solvent and the molecule's hydrogen. Now this bond is inherently weak but a large number of such bonds in solution require greater effort to break and so the boiling point of such a system increases and so does water solubility. So water solubility is really an outcome of weak intermolecular forces between the water molecules and the solute molecules.

    As the size of the carbon chain increases, the molecule becomes bulkier and the inductive effect of the carbon chain increases, placing a larger partial negative charge on the oxygen. The greater the negative charge on the oxygen (partial charge) the smaller is the oxygen atom's tendency of giving up its hydrogen for hydrogen bonding as the hydrogen is more strongly attracted to the oxygen--less available for weakly bonding with an external ato. The increase in size of the carbon chain and or increase in branching of a carbon chain also decrease the acidity of the hydroxy group's hydrogen atom.

    Steric effects are also operative. It is conventional to say that lower alcohols like methanol and ethanol are soluble in water. As the number of carbon atoms increases however, we cannot make such a generalization. In fact the alcohol actually contains a polar and a nonpolar part (a hydrophilic and hydrophobic part I think its called...) and the effect in solution is a result of the amount the nonpolar part (the carbon chain minus the hydroxy group and any other polar groups present) outweighs the polar part in simple terms.

    Hope that helps...

  6. Nov 1, 2004 #5
    one quick question though. as chem_tr suggested, we should use warm water to clean latex paint. however, how does using hot water allow the removal of latex paint? is it because latex paint will dissolve in water, allowing both the removal of water and the paint at the same time?

    by the way. thanks maverick and chem_tr
  7. Nov 1, 2004 #6


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    As latex paints are water-soluble pigment-based paints, water can dissolve them and separate from the surface by gentle rubbing and using warm water (this is not always necessary; cool water does the work as well as warm one). However you cannot do the same thing for alkyd-based paints, since they are insoluble in water, so however hard you try, water (either warm or cool) won't help you. This is a matter of solubility and solvatation.

    This is my 300th message :smile:
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