June 30, 2022, 01:03:24 PM
Forum Rules: Read This Before Posting


Topic: Question relating to moles, Mass, Molecules of water crystallisation  (Read 6585 times)

0 Members and 1 Guest are viewing this topic.

Offline earthnation112

  • Regular Member
  • ***
  • Posts: 94
  • Mole Snacks: +2/-0
Re: Question relating to moles, Mass, Molecules of water crystallisation
« Reply #15 on: May 01, 2016, 09:12:54 AM »
I think I finally see where the confusion is.

Question is a bit ambiguous. "The number of molecules of water of crystallization in Borax" can mean both x in ·xH2O (and I believe this is what they are asking for), and the number of molecules in the whole sample.

What you did is OK, that's the correct way of finding x.

To calculate total number of molecules it is enough that you have determined mass of water in the sample from the experimental data.

If I was to find the "number of molecules of water of crystallisation in Borax" do I simply take the "Weight of water in the borax sample " answer and multiply it by 10 since x=10 and then multiply that by Avogadro's number? Or would I take the  "Weight of water in the borax sample " and multiply this directly by Avogadro's number? Cheers

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27120
  • Mole Snacks: +1761/-405
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Question relating to moles, Mass, Molecules of water crystallisation
« Reply #16 on: May 01, 2016, 01:39:00 PM »
Say you have 2 g of water.

Does the number of molecules depend on where the water comes from and what was the formula of the original compound that contained it?

Is 2 g of water taken from CuSO4·5H2O different from 2 g of water taken from Na2B4O7·10H2O?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline earthnation112

  • Regular Member
  • ***
  • Posts: 94
  • Mole Snacks: +2/-0
Re: Question relating to moles, Mass, Molecules of water crystallisation
« Reply #17 on: May 01, 2016, 04:36:04 PM »
Say you have 2 g of water.

Does the number of molecules depend on where the water comes from and what was the formula of the original compound that contained it?

Is 2 g of water taken from CuSO4·5H2O different from 2 g of water taken from Na2B4O7·10H2O?

No it doesn't matter because to know the amount of molecules present when given grams of a substance you  would need to:

1. Divide the grams of the substance by its molar mass which gives the moles of a substance.
2. Then you need to multiply this number by  Avogadro's number to get the amount of molecules.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27120
  • Mole Snacks: +1761/-405
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Question relating to moles, Mass, Molecules of water crystallisation
« Reply #18 on: May 01, 2016, 06:20:56 PM »
Do you see how it answers your question?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline earthnation112

  • Regular Member
  • ***
  • Posts: 94
  • Mole Snacks: +2/-0
Re: Question relating to moles, Mass, Molecules of water crystallisation
« Reply #19 on: May 01, 2016, 06:32:46 PM »
Do you see how it answers your question?

Yes I see, I just need to:

1. Divide the grams of the substance by its molar mass which gives the moles of a substance.
2. Then you need to multiply this number by  Avogadro's number to get the amount of molecules.

1. 2.431463775/18.01528 = 0.1349667491 moles
2. 0.1349667491* 6.022 x 1023  = 8.1276976 x 1022

Thanks for all the help finally got there 8) Once again cheers.

Sponsored Links