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Homework Help: Electric Forces Problem

  1. Jul 9, 2008 #1
    First post here, so I wanted to say hello first of all. Must admit this board seems quite helpful. Anyways, here's my problem I'm having issues with, any help would be great.

    Water has a mass per mole of 18.0 g/mol, and each water molecule (H2O) has 10 electrons. (a) How many electrons are there in one liter (1.00x10^-3) of water? (b) What is the net charge of all these electrons?

    I'm not even sure where to get started which is my main problem. Thanks again.
  2. jcsd
  3. Jul 9, 2008 #2

    Doc Al

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    Hint: What's the density of water?
  4. Jul 9, 2008 #3


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    A mole of water contains Avogadro's number of molecules, 6.02*10^23 and it has a mass of 18g. A liter of water has a mass of 1000g. So how many moles in one liter? Hence how many molecules in one liter? Hence how many electrons in one liter? Etc. Does that get you started?
  5. Jul 9, 2008 #4
    I think I can maybe go with that... It's been a while since I've done anything physics related so I'm extremely rusty. Thanks, I'll be back quick with a response.
  6. Jul 9, 2008 #5
    OK, I took that info and did my best to work out the problem... I came up with 3.34x10^26 which was very close to one of the answer choices provided by my professor. Anyone mind double checking me?

    The other 4 choices were:

  7. Jul 9, 2008 #6


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    That looks fine to me.
  8. Jul 9, 2008 #7
    Awesome, thanks a ton!
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