Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: nikita on May 27, 2008, 05:39:15 PM
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Hi! i am actually in college, but this is general chem and chap 1, so i decided to put it in here. i am an adult going back to college, so hs chem was long ago for me. i am working on unit conversion and densities, and i have a few problems that i am confused by, or maybe i just dont know where to start.
a 5.79 mg piece of gold is hammered into gold leaf of uniform thickness with an area of 44.6 cm^2. what is the thickness of the gold leaf?
i understand 5.79mg to be the mass here. i also guess that if i have the area, i am then looking for the h, in LxWxH?
i also guess that 19.3 grams is going to come into play here?
no, i am totally lost. i think its because i may need a formula that i dont know. i dont even know what to convert into what. any pointers? im not asking for the answer because i have that, maybe just a jumpstart, as i think i can figure it out if i just knew where to start. thanks.
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Not sure if this will help at all but...
I believe since you know its gold you can find its density (You were right with 19.3 g/cc), and from there you have its density, mass, and area.
Then calculate its volume = mass/density.
Then finally its thickness = volume/area.
I think this is what needs to be done but I'm not entirely sure. Hopefully someone else with more knowledge comes around and checks it out. Hopefully I helped a little bit. :)
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ok, i thought about it longer and decided to convert the mg mass to g and then i have my mass and density.
i get
19.3g = .00579g/v and v then = 3.00 x 10^-4
so i have the volume and mass, how do i find the thickness?
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You have volume - and you first instict of LxWxH was correct. Just LxW is already a surface which you are given.
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.0003 = 44.6x
.0003/44.6 = 44.6x/44.6
x = 6.73 x 10^-6cm^2
i know that is the right answer. did i do this correctly, or did i make up a crazy way of doing it?
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Rounded I got the same result and yes I believe this is the correct approach... ;D
*Edit* I'm not sure about college, but a lot of my teachers are picky about the showing of units and how they are simplified in the equations as well.
In this case it went from
Volume (cm3) = mass (g) / density (g/cm3) [g cancel]
Thickness (cm) = volume (cm3) / area (cm2) [which leaves you with cm]
As far as I can tell this is the correct method of choice for this problem.
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this is how i did it:
5.79mg x .001g/1mg = .00579g (canceling out mgs)
19.3 g = .00579g/v (19.3 grams the density of gold)
v= .0003cm^2 (yes?)
so i took L x W x H for the volume formula with
v = .0003g
.0003g = 44.6cm^2 (LxW = 44.6, so i put in x for the height) i really dont think that is the right way to do it, is it?
dividing, i get
6.73 x 10^-6g/cm^2 is the thickness?
i have a few more questions about other problems, but i guess its prudent to write a new thread. oh, and thanks so much for the help thus far!