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!

Statistics Problems from Physical Chemistry

  1. Sep 13, 2012 #1
    1. The problem statement, all variables and given/known data
    The following data were obtained for trace elemental zinc in a particular sample of high purity (%Au> 99.99%). The results are given in mg Zn/ kg Au.

    15.38, 15.17, 15.33, 14.88, 14.71, 15.42, 15.60, 15.22

    Find the zinc content and the uncertainty at 95% confidence limit.

    2. Relevant equations

    Molecular weight of gold: 196.966569 g mol-1

    3. The attempt at a solution
    I found the average of all the values, then converted to mg of Zinc by multiplying the kg of Au. I'm not really sure on how to find the uncertainty at 95% confidence.
     
  2. jcsd
  3. Sep 13, 2012 #2

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    Find the sample mean and sample standard deviation of your data above, then use the t-distribution to determine a confidence interval.

    If you have never seen this type of material before, or if your textbook or notes have not done it, the assignment question could be counted as "unfair": this type of material is not always easy to grasp, and it takes practice to understand it. On the other hand, if it is in your book or notes, why don't you just follow the method therein?

    RGV
     
  4. Sep 13, 2012 #3
    So multiplying by kg of Au was right?
     
  5. Sep 14, 2012 #4

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    It depends on what you want to measure. You could just take the original measurements, without any multiplication, and that would give you inferences about mg of Z per kg Au. If you want something else, do the conversion.

    However, this has nothing at all to do with the question you were asked, which was about confidence intervals.

    RGV
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook