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Chemistry questions

  1. Nov 22, 2013 #1


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    I'm taking a course in chemistry and I need some help, I have some questions :
    1.Why do ions, strong acids,bases etc. conduct electricity well ?

    2.In the periodic table, are the masses of atoms in amu or grams? what's the difference? and why is Carbon 14 the standard ? why do we need a standard in first place, in other words why can't we just measure the mass without relating to carbon 14 ?

    find the molarity of each ion in 0.50M Co(NO3)2.
    So we put the equation:
    Co(NO3)2 --> Co2+ +2NO3-
    Co2+ = 0.50M
    NO3- = 1.0M
    My question is why did we multiply with the coefficient? how is it that by multiplying the coefficients with concentration we immediately get the answer? I just can't find the logic here.

  2. jcsd
  3. Nov 22, 2013 #2


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    Ions themselves do not conduct electricity.They conduct electricity when in molten or aqueous ionic compounds.
    Acids and based have H+ and OH- ions,respectively.And the ions such as NO3- for Nitric acid .Na+ for Sodium Hydroxide.
    When we pass electricity through this molten/aqueous ionic compounds,Acids,bases, they decompose.This happens by electrolysis
  4. Nov 22, 2013 #3


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    2. Carbon 14 is not the standard. C14 is a radioactive isotope of carbon. Its chief use is in dating organic material. Perhaps you mean Carbon 12.
  5. Nov 22, 2013 #4
    If I tell you I have a parking lot with 100 cars in it and I ask you to do an inventory of car parts, will you need to go and count each part on each car? Can you tell me how many tires, steering wheels, headlights, catalytic converters, engines etc there are?
  6. Mar 5, 2014 #5
    This is also because in strong acid there are more hydrogen ions present to carry the charge (of electricity)

    Sent from my iPhone using Physics Forums
  7. Mar 5, 2014 #6
    When the charged ions in aqueous solution are in an electric field, the ions are free to migrate through the water toward the anode (negative ions) and cathode (positive ions). This constitutes electric current flow.

  8. Mar 5, 2014 #7


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    For question 2 these things are often historical but at the same time rational and useful on the whole.

    Most of the answer should be evident from your own experience if you have done any amount of chemistry. Would you prefer to every time remember or look up the mass of the C atom, and then remember or look up the mass of the H atom, and of the O atom, and the N atom every time you do a calculation about a compound containing these? It is far more convenient to remember their ratios, which are all you need for chemical calculations anyway, are approximately 14: 1: 16: 14. You have probably used this a number of times, and for many of us it is the sort of thing for which we say 'I wish I had 10 cents for every time...'

    At the time atomic masses emerged as a concept they were only known as ratios in chemistry. It made sense to define the hydrogen atomic mass as 1. And when I say hydrogen, or 'the' hydrogen atom, that meant the bulk hydrogen that you can normally get in a laboratory on earth. They had to imagine all the atoms were identical, they knew nothing of isotopes and that natural hydrogen atoms are really three types, and similarly for other elements. They did know that the atomic mass ratios for these mixtures that they didn't know were mixtures were not exact whole numbers, though most of them were close to whole numbers (and someone did suspect the obvious explanation of that fact, but there wasn't much anyone could do about it at the time).

    H = 1 was convenient to start with. But standards get officially redefined constantly because it is found that something other than the one originally used lends itself to more exact measurements. But they at the same time try to make the new units agree approximately with the old so nothing or as little as possible changes for those who work to only some approximation. So for this reason they have redefined atomic masses the way you know and H instead of 1 is 1.008 or whatever.

    You might think that some of that you could have worked out for yourself. :biggrin:
    Last edited: Mar 5, 2014
  9. Mar 6, 2014 #8


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    Obviously I meant to write 12:1:16:14 there. :redface:
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