1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Tough Chemistry Question

  1. Feb 1, 2005 #1
    Hello, I got this really hard question on my chemistry assignment and I don't know where to start; I am completely lost.

    If 125g of magnesium sulfate heptahydrate is completely dehydrated, how many grams of anhydrous magnesium sulfate will remain?

    Any help would be greatly appreciated!
     
  2. jcsd
  3. Feb 1, 2005 #2
    Do you know the formula for the above mixture ? What does the formula tell you about how much each part contributes to the mass ?
     
  4. Feb 1, 2005 #3
    is it Mg2SO3 . 7H2O?

    I could probably solve this if I knew what anhydrous meant.
     
  5. Feb 1, 2005 #4

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    That's not SULPHATE,that's a wrong version of SULPHYTE.You need another formula...

    Anhydruous=without water...

    Daniel.
     
  6. Feb 1, 2005 #5
    I am sorry, I do not get this; could you please rephrase it for me?What's sulfyte?
    and what is a difference between dehyration and anhydrate?
     
    Last edited: Feb 1, 2005
  7. Feb 1, 2005 #6

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    [itex]MgSO_{3} [/itex] is MAGNESIUM SULPHYTE and [itex] MgSO_{4} [/itex] is MAGNESIUM SULPHATE.One of them comes from the sulphurous acid,the other from sulphuric acid...

    DEHYDRATION=losing water.
    ANHYDROUS=without water...

    Daniel.
     
  8. Feb 1, 2005 #7
    I finally get the question but how do I solve it?
    I done this before but with knowing the weight of each elements.
     
    Last edited: Feb 1, 2005
  9. Feb 1, 2005 #8

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    Well,1 mole of [itex] MgSO_{4}\cdot 7 H_{2}O[/itex] has a certain mass...Can u compute it...?How about the mass of 1 mole of [itex] MgSO_{4} [/itex] ??

    Daniel.
     
  10. Feb 2, 2005 #9

    GCT

    User Avatar
    Science Advisor
    Homework Helper

    You can observe the formula and from this find the final mole value of magnesium sulfate heptahydrate; find the molar mass of the compound and then find the realistic mole value using the 125 grams.

    You know that for every one mole of the compound, there is 7 moles of H20. This should give you a stoichiometric ratio 7 moles of H20/1 mole of the compound. Convert using this ratio to moles of water. From this mole value, convert to grams of water. Subtract this value from 125, and that should be your answer.
     
  11. Feb 2, 2005 #10

    saltydog

    User Avatar
    Science Advisor
    Homework Helper

    I'd like to help:

    mol. wgt of MgS04*7H20 = 246.3
    mol.wgt of MgS04 = 120.3

    Thus, the ratio of anhydrous/hydrous (without water/with water) = 0.488

    Thus, when you remove the water from 125 grams of the hydrate, the remaining is:

    125*0.488=61 grams MgSO4 left.

    I believe that's right. It's been a while and I don't want to make it worst for you.

    Salty
     
    Last edited: Feb 2, 2005
  12. Feb 2, 2005 #11
    Thank you all, I got how you solve it now.
    It seems so easy after you get what is doing on
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Tough Chemistry Question
  1. Tough question (Replies: 1)

  2. Tough Question? (Replies: 1)

  3. Tough moments question (Replies: 9)

Loading...