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Math Help - Density problems (work check)

  1. #1
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    Density problems (work check)

    Here's a question I was working on:

    A crystal of sulfur has a density of 1.94 g/cc.
    (a) What is the mass (in grams) of a sulfur crystal with a volume of 2.534 cm3?
    (b) What is the density of sulfur in kg/m3?
    (c) What is the volume (in mL) of a sulfur crystal that weighs 9800 mg?



    Here is the solutions I've arrived at:

    (a) Well we know D = M / V thus rearrange as M = D * V to obtain the value of 4.91596g which I rounded to 4.92g as taking into account significant digits.

    Correct or incorrect?

    (b) I know D = 1.94 g/cc thus I can write 1.94 g/cc / 1000 = 0.00194 kg/m3

    I'm not so sure about the sig figs on that final answer there, or if it's even the correct conversion at all?

    (c) I rearrange as such:  V = M / D and plugged in 9800mg / 1.94g per cc = 5051.5mL

    Is this correct?


    If you could help me with the mistakes I made and offer advice, etc. that would be appreciated. Thanks a lot for reading.
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  2. #2
    No one in Particular VonNemo19's Avatar
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    Detroit, MI
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    Quote Originally Posted by hemi View Post
    Here's a question I was working on:

    A crystal of sulfur has a density of 1.94 g/cc.
    (a) What is the mass (in grams) of a sulfur crystal with a volume of 2.534 cm3?
    (b) What is the density of sulfur in kg/m3?
    (c) What is the volume (in mL) of a sulfur crystal that weighs 9800 mg?



    Here is the solutions I've arrived at:

    (a) Well we know D = M / V thus rearrange as M = D * V to obtain the value of 4.91596g which I rounded to 4.92g as taking into account significant digits.

    Correct or incorrect? correct

    (b) I know D = 1.94 g/cc thus I can write 1.94 g/cc / 1000 = 0.00194 kg/m3

    I'm not so sure about the sig figs on that final answer there, or if it's even the correct conversion at all? corect. If your worried about sig figs switch to scientific notation.

    (c) I rearrange as such:  V = M / D and plugged in 9800mg / 1.94g per cc = 5051.5mL you're dividing mg's by g's?

    Is this correct?


    If you could help me with the mistakes I made and offer advice, etc. that would be appreciated. Thanks a lot for reading.
    ..
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  3. #3
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    Thank you very much for the reply again Von. As for (c), I take it I'd need to make both units the same. When I do this however, that is, convert 1.94g per cc to 0.00194 mg per cc I get the same result when plugging it back into my equation.


    I have a feeling I'm just doing this wrong. What direction should I look in?
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  4. #4
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    I've reworked the question (c) and this is my work...

    (9800mg) (\frac{1cm^3}{1.94g}) (\frac{1g}{1000mg})


    And the final answer is equal to 5mL, is this technique correct?
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