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Chemistry: Significant Figures and Addition

  1. Feb 18, 2009 #1
    1. The problem statement, all variables and given/known data

    I just wanted to know if I wrote the answer with the correct number of significant figures for this addition problem.

    0.00015 M + 0.00004 M + 0.00011 M = 0.00030 M (Correct?)


    2. Relevant equations

    See above.

    0.00015 M + 0.00004 M + 0.00011 M = ?

    3. The attempt at a solution

    See Part 1.

    All of the original numbers have 5 decimals places, but only the first and third values have 2 significant figures. (The second has 1 significant figure.) Therefore, the final answer must be expressed with 5 decimal places, and will have 2 significant figures (0.00030 M)?

    Thank you.
     
  2. jcsd
  3. Feb 18, 2009 #2

    symbolipoint

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    You have all the place values known to the fifth decimal place, so yes, take to the fifth decimal place.
     
  4. Feb 26, 2009 #3

    chemisttree

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    I would say that the answer was 0.0003. If you were to express the answer to 5 places you would get 0.00029... that is two sig figures and you are allowed one. 0.00030 has two sig figures and you are allowed one.
     
  5. Feb 26, 2009 #4

    Borek

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    0.111+0.222+0.0001=0.3 then?
     
  6. Feb 26, 2009 #5

    chemisttree

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    Yikes! Of course you are correct, Borek. Good catch. You will also note that I cannot even be trusted to correctly add three numbers together as well...
     
  7. Feb 26, 2009 #6

    symbolipoint

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    We each did some rethinking and are a bit better for doing so.
     
  8. Feb 26, 2009 #7
    haha should you really be helping people with that kind of math? XD just kidding :P
     
  9. Feb 26, 2009 #8

    chemisttree

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    Sometimes I amaze myself.
     
  10. Feb 27, 2009 #9

    Borek

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    Don't feel alienated :rofl:
     
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