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!

Chemistry Problem III

  1. Sep 26, 2007 #1
    Question:

    Given
    mass of hexaammine complex [Ni(NH3)6](NO3)2 is 0.0937 g
    mass of Ni2+ is 0.0193 g

    if the mass of [Ni(NH3)6](NO3)2 was 0.0886 g instead of 0.937g, this would indicate that the hexaammine complex was not pure and some ammonia had been lost. Calculate the value of n in the formula [Ni(NH3)n](NO3)2


    my attempt:

    - Take the mass of Ni2+ and find the moles of it using Ni2+ molar mass. This mole would then be the same as the moles of the complex (1:1 ratio) --> i found to be 0.0003288 moles

    - then take the grams of the complex 0.0886 g and divide by that mole: 0.0886g/0.0003288moles = 264.4404 g/mol which would be the molar mass of the complex

    - then i subtracted the molar masses of Ni2+ and (NO3)2 from that molar mass and what is left is the amount of (NH3)n. Then i took that amount and divided by the molar mass of one NH3 to see how many NH3 I have.

    am I thinking right?
     
  2. jcsd
  3. Sep 27, 2007 #2

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You are well on your way.
     
  4. Sep 29, 2007 #3
    i keep getting the wrong answer....what am i doing wrong?
     
  5. Sep 29, 2007 #4
    so here is what i did

    0.0193g Ni x (1 mol Ni/58.693g) x (1mol [Ni(Nh3)6](NO3)2/ 1 mol Ni) = 3.288 E-4 moles of [Ni(Nh3)6](NO3)2

    then i took 0.0886g and divide by this moles to get the molar mass
    0.0886g/3.288 E-4 moles [Ni(Nh3)n](NO3)2
    = 269.44 g/mol

    then i substracted Ni (58.693g/mol) and (NO3)2 (124.008g/mol) from that molar mass
    269.44 - 58.693 - 124.008
    86.739 g/mol

    then take this number and divide by (NH3) molar to see how many NH3 there are:
    (86.739g/mol) / (17.031g/mol)
    = 5.09 NH3

    so n is equal to 5.09.... this answer is still incorrect when i entered into the computer for grading ><

    what am I doing wrong!!!!!!!!!??????????
     
  6. Sep 29, 2007 #5
    did you enter 5 or 5.09? n should be a whole number
     
  7. Oct 2, 2007 #6

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    How many significant figures are you asked to provide? Generally you would use an integer value if you were trying to determine the empirical formula for a pure substance. In this case the sample may be a mixture of the hexamine, pentamine, etc... and so a non-integer value for n may be correct.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Chemistry Problem III
  1. A chemistry problem (Replies: 4)

  2. How many moles of ATP (Replies: 3)

  3. Chemistry problem (Replies: 9)

  4. Chemistry problem (Replies: 1)

Loading...