Results are out! Find what you need...fast. Get quick advice or join the chat
Hey! Sign in to get help with your study questionsNew here? Join for free to post

Do simple molecular covalent substances dissolve in water, and why?

Announcements Posted on
Applying to Uni? Let Universities come to you. Click here to get your perfect place 20-10-2014
    • Thread Starter
    • 1 follower
    Offline

    ReputationRep:
    I have my GCSE Chemistry on Monday and cramming a bit of revision this weekend. Though I'm getting lots of different answers on the internet for this question, and I'm terrible and chemistry and confused. It's a question with a table and different substances. This one has a low melting and boiling point and doesn't conduct electricity, even as a liquid. That means it's simple molecular covalent right? I also need to suggest why it will or won't dissolve...Please help! Thanks guys.
    • 0 followers
    Offline

    ReputationRep:
    Correct it is a simple molecular structure because it doesnt conduct electricity and low melting and boiling point. Why do you think it might not or will dissolve. well it all depends on the polarity of the molecule
    is there anymore information or you could talk about intermolecular force (although im not sure if you do this for GCSE. Hmm use your information and make a reasonable deduction
    • 20 followers
    Offline

    ReputationRep:
    (Original post by Education_1)
    Correct it is a simple molecular structure because it doesnt conduct electricity and low melting and boiling point. Why do you think it might not or will dissolve. well it all depends on the polarity of the molecule
    is there anymore information or you could talk about intermolecular force (although im not sure if you do this for GCSE. Hmm use your information and make a reasonable deduction
    I agree, I'm not sure you can deduce whether something will dissolve or not using only GCSE knowledge and application
    • 4 followers
    Offline

    ReputationRep:
    (Original post by Stevo F)
    I agree, I'm not sure you can deduce whether something will dissolve or not using only GCSE knowledge and application
    Intermolecular forces are on the syllabus but I was always under the impression that dissolution referred to a compound being split into ions when it comes into contact with water yet in past papers they say that hydrogen chloride is dissolved in Methylbenzene, which of course does not split it into ions, but I don't understand what the actual definition of dissolve (or dissolution) is. Could someone please explain this to me?
    • 0 followers
    Offline

    ReputationRep:
    (Original post by Stevo F)
    I agree, I'm not sure you can deduce whether something will dissolve or not using only GCSE knowledge and application
    Yup it mostly depend on how polar the molecule is ..Maybe OP; is there any more information that you could provide or something (maybe structure of the molecule). I may have confuse you if you dont do polarity of molecules; OP does this help?
    http://www.bbc.co.uk/scotland/learni...bsp_rev4.shtml
    • 0 followers
    Offline

    ReputationRep:
    (Original post by Umackjiggles)
    Could someone please explain this to me?
    Dissolving is just going into solution, it doesn't really matter how. So some things break into ions (which are charged) so can come associated with water molecules and hence are dissolved. Other substances are charged nonetheless (like chloromethane) and so can associate with water molecules.

    The associations occur because of the charges and hydrogen bonds occur between the H on the H2O and the charged molecule - be it ion or polar.
    • 32 followers
    Offline

    ReputationRep:
    It depends on the polarity, e.g. C2H6, although being simple covalent in structure, is non-polar, and thus will not dissolve in water very well.

    It would, however, dissolve in a non-polar solvent, e.g. cyclohexane, C6H12.

    Essentially, polar solutes dissolve in polar solvents and non-polar solutes dissolve in non-polar solvents. This explains why oils and fats cannot dissolve in water, as oils and fats are non-polar, where as water is polar.
    • 0 followers
    Offline

    ReputationRep:
    Educations_1 is right, it all depends on how polar the molecule is.
    Dissolution is really to do with the affinity that the solute has for the solvent (liquid medium)

    A non polar substance (like alkenes and alkanes) will dissolve well in nonpolar liquids.
    Likewise ionic and polar substances will dissolve best in polar liquids (such as Water)

    Since this is GCSE we can guess we're talking water as the solvent. This means that ionic substances will dissolve in them as well as polar substances. For GCSE this means assume all salts (except the insoluble exceptions) and the acids dissociate and dissolve in water.
    • 1 follower
    Offline

    ReputationRep:
    (Original post by ScienceConfusion)
    I have my GCSE Chemistry on Monday and cramming a bit of revision this weekend. Though I'm getting lots of different answers on the internet for this question, and I'm terrible and chemistry and confused. It's a question with a table and different substances. This one has a low melting and boiling point and doesn't conduct electricity, even as a liquid. That means it's simple molecular covalent right? I also need to suggest why it will or won't dissolve...Please help! Thanks guys.
    In general, yes, low melting and boiling point and non-conductance of electricity suggests that the compound is a simple covalent molecule.

    As for solubility, you first must remember that it is all relative. Almost all compounds are soluble in water, its just that some are massively more soluble than others. Iron is soluble in water, it's just that salt (sodium chloride) is much more soluble. Glucose is even more soluble than salt etc.

    Water (H2O, so 2 hydrogens and 1 oxygen) is a polar molecule. The oxygen atom attracts the electrons in the O-H covalent bond towards itself, and so is slightly negatively charged; the hydrogen, losing some of its electrons is slightly positively charged. This is because oxygen is more electronegative than hydrogen. If you haven't come across electronegativity before, then you can just remember that in general, molecules with different atoms are polar whereas molecules with same atoms are non polar (e.g. O=O is non-polar as its 2 atoms are the same whereas H-F is polar as its 2 atoms are different).

    Polar solvents will tend to dissolve polar compounds more than non-polar compounds and vice versa. Water is a polar solvent, and so will tend to dissolve other polar compounds better. If your mystery compound is polar e.g. H-F, then it will be very soluble; if it is non-polar e.g. O=O, the it won't be very soluble.

    This explains why we have a specialized protein for transporting oxygen in our blood. O=O is non-polar and therefore doesn't dissolve well in our blood, so to carry it in high concentrations, we need to bind it to haemoglobin protein. Carbon dioxide, on the other hand, O=C=O, is polar because of the large difference in electronegativity between O and C and can therefore just be carried by dissolving it in the blood.

    Hope this helps.
    • Thread Starter
    • 1 follower
    Offline

    ReputationRep:
    (Original post by qiaoyu.he)
    In general, yes, low melting and boiling point and non-conductance of electricity suggests that the compound is a simple covalent molecule.

    As for solubility, you first must remember that it is all relative. Almost all compounds are soluble in water, its just that some are massively more soluble than others. Iron is soluble in water, it's just that salt (sodium chloride) is much more soluble. Glucose is even more soluble than salt etc.

    Water (H2O, so 2 hydrogens and 1 oxygen) is a polar molecule. The oxygen atom attracts the electrons in the O-H covalent bond towards itself, and so is slightly negatively charged; the hydrogen, losing some of its electrons is slightly positively charged. This is because oxygen is more electronegative than hydrogen. If you haven't come across electronegativity before, then you can just remember that in general, molecules with different atoms are polar whereas molecules with same atoms are non polar (e.g. O=O is non-polar as its 2 atoms are the same whereas H-F is polar as its 2 atoms are different).

    Polar solvents will tend to dissolve polar compounds more than non-polar compounds and vice versa. Water is a polar solvent, and so will tend to dissolve other polar compounds better. If your mystery compound is polar e.g. H-F, then it will be very soluble; if it is non-polar e.g. O=O, the it won't be very soluble.

    This explains why we have a specialized protein for transporting oxygen in our blood. O=O is non-polar and therefore doesn't dissolve well in our blood, so to carry it in high concentrations, we need to bind it to haemoglobin protein. Carbon dioxide, on the other hand, O=C=O, is polar because of the large difference in electronegativity between O and C and can therefore just be carried by dissolving it in the blood.
    Hope this helps.

    THANK YOU SO MUCH. I'm eternally grateful! You've helped me so much with Chem revision, I thank you again. Fantastic answer, thanks for your help. :rolleyes:

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: May 19, 2012
New on TSR

Personal statement help

Use our clever tool to create a PS you're proud of.

Article updates
Reputation gems:
You get these gems as you gain rep from other members for making good contributions and giving helpful advice.