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Specific heat capacity of brass

  1. Sep 26, 2012 #1
    1. The problem statement, all variables and given/known data
    i getting the wrong the answer

    i am

    trying to find the specific heat capacity of brass
    using copper calorimeter
    Data :
    mass of brass bob= 32.5gm
    mass of calorimeter = 39.7 gm
    mass of water + calorimeter = 93.9gm

    mass of water = 93.9 - 39.7 = 54.2g

    specific heat of water = 4.2 j/gm deg Cel
    specific heat of copper = 0.382 j/gm deg cel

    Temp of water = 23 deg cel
    Temp of brass = 94 deg cel

    temp of mixture = 47 deg cel




    2. Relevant equations
    formulas used..

    part A

    (Mc*cc + Mw*cw)(T1-T2)

    (mass of the calorimeter* specific heat of the calorimeter + mass of the water*specific heat of the water)*Fall in the temperature.


    Part B
    C=H/mΔT



    3. The attempt at a solution

    part A being solved

    (mass of the calorimeter* specific heat of the calorimeter + mass of the water*specific heat of the water)*Fall in the temperature.

    (39.7 * 0.386) + (54.2 * 4.2) * (47-23)
    (15.3242 + 227.64) * 24

    242.9642 * 24

    5831.1408

    part b being solved.

    C=H/mΔT
    = 5831.1408/ 32.5 * 47

    = 5831.1408 / 1527.5

    = 3.8174407856

    specific heat of brass = 3.8174407856 j/gm deg cel




    this answer is wrong

    the expected answer is 0.3817

    where am i going wrong....
     
  2. jcsd
  3. Sep 26, 2012 #2

    CWatters

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    Science Advisor
    Homework Helper

    The SHC of brass should be roughly similar to that of copper because brass is made from copper so the book answer is probably correct and google confirms it..

    In which case the heat lost by the brass is

    E = 0.3817 * 32.5 * (94-47) = 583 Joules

    If the water (alone) rises from 23 to 47 then the energy gained by the water is

    E = 4.2 * 54.2 * (47-23) = 5463 Joules

    so I think there is something wrong with the original data.
     
  4. Sep 27, 2012 #3
    hi CWatters

    I and my colleague tried this experiment many times . but we come to almost the same wrong answer.

    we are not able to find where could the data go wrong.
     
  5. Sep 27, 2012 #4

    gneill

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    Staff: Mentor

    The result would come out better if the mass of the brass happened to be 10x higher (325gm rather than 32.5gm). Possible transcription error?
     
  6. Oct 2, 2012 #5
    Thanks sir for your prompt reply

    But I checked the mass there is no transcription error

    It is 32.5 grams

    But similarly I too doubt that somewhere there is an issue with a decimal point

    But I can't figure out
     
  7. Oct 2, 2012 #6

    gneill

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    Staff: Mentor

    Is this a problem from a text, or is it data reduction from a laboratory experiment that you have performed? You mention that you and your colleague "tried the experiment many times"...
     
  8. Oct 2, 2012 #7
    It is a data from a lab experiment
     
  9. Oct 2, 2012 #8

    gneill

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    Staff: Mentor

    Ah. I see. After examining the procedure and the equipment and after a trial run, did you make a list of possible sources of error? Is there any place that heat might come from or escape to during the experimental runs?
     
  10. Oct 2, 2012 #9

    CWatters

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    Homework Helper

    Is it possible the thermocouple is measuring the temperature of the water close to the brass bob and that it's not 47C everywhere?
     
  11. Oct 2, 2012 #10
    Thanks again

    I'll verify the points you suggested and get back to you later

    And also go through possible errors
     
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