Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Helppppp Stoichiometry (sp?)

  1. Feb 7, 2005 #1
    1. Aluminum chloride (15.0g) + sodium hydroxide (15g) = double displacement reaction.Predict mass of aluminum hydroxide produced. What mass of the excess reagent remains unreacted?

    2. What mass of copper(II) sulfate pentahydrate is needed to prepare 150.0 mL of a 0.125mol/L solution?

    How do I find them?
     
  2. jcsd
  3. Feb 7, 2005 #2
    2. convert 150 ml to L then multiply Volume * Concentration. Therefore = (0.150 L)(0.125 mol/L). This will get you the number of moles of copper (II) sulfate pentahydrate. Then multiply the Molecular Weight of copper (II) sulfate pentahydrate by the number of moles and you will get the number of grams. Hope that helps.
     
  4. Feb 7, 2005 #3
    does the Molecular Weight of copper (II) sulfate pentahydrate = 164.21g/mol?
     
  5. Feb 7, 2005 #4
    Not sure, if you calculated it using the molecular weights then it's probably right.
     
  6. Feb 7, 2005 #5
    copper(II) sulfate pentahydrate

    This is what I did:

    (molar mass of Cu * 2 ) + ( molar mass of S) + (molar mass of H * 5
     
  7. Feb 7, 2005 #6
    Cu+S+O*4+5*(H*2+O)

    The molecular formula is CuSO4(H2O)5
     
  8. Feb 7, 2005 #7
    Therefore your molecular weight is incorrect. Try again.
     
  9. Feb 7, 2005 #8

    I re-calculated it and it came out to 249.71g/mol??
     
  10. Feb 7, 2005 #9

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    It should come out 250.

    What about the first problem??Can u do it...?

    Daniel.
     
    Last edited: Feb 7, 2005
  11. Feb 7, 2005 #10
    63.546+32.066+15.9994*4+5*(1.00794*2+15.9994)
    I believe it should come out to be 249.686
     
  12. Feb 7, 2005 #11
    1. Is this right:

    Mol of AlCl3 = 0.112mol
    Mol of NaOH = 0.125mol

    mass = (0.112mol)(78.03g/mol)
    = 8.74g

    b)do I multiply 0.125 mol by the mols of 3NaCl. Then subtract 8.74 from the anwser?
     
  13. Feb 7, 2005 #12
    Depending on the number of the significant figures used I believe that your answer should be accurate enough.
     
  14. Feb 7, 2005 #13
    The final answer for question 2 should be 4.68 g.
     
  15. Feb 7, 2005 #14

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    No,no,no,no,no.No such precision required whatsoever.YOUR FINAL ANSWER IS APPROXIMABLE TO 250... :tongue2:

    Daniel.
     
  16. Feb 7, 2005 #15

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    The remaining mass is of NaOH indeed & is roughly 1.5g

    Daniel.
     
  17. Feb 7, 2005 #16
    How did you get that?
     
  18. Feb 7, 2005 #17

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    1 mole AlCl_{3}----------------->133.5g
    1 mole NaOH-------------------------> 40g

    The chemical reaction:
    [tex] 3NaOH+AlCl_{3}\rightarrow Al(OH)_{3}+3NaCl [/tex]

    So
    3 moles NaOH/120g react with 1mole AlCl_{3}/133.5 g.
    x g NaOH react with 15g of AlCl_{3}

    Find "x" & subtract it from 15.

    Daniel.
     
  19. Feb 7, 2005 #18
    :confused:
     
  20. Feb 7, 2005 #19

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Samantha, before solving problems on stoichiometry, you need to learn how to write and balance equations. I suggest you first work on this, and get your basics clear. It may take a while but it's very important, and essential to your being able to solve any kind of chemistry problem.
     
  21. Feb 7, 2005 #20
    I got the same equation but I don't get the calculations..I should work on that.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Helppppp Stoichiometry (sp?)
  1. SP Carbon Orbitals (Replies: 3)

Loading...