Homework Help: Chemistry

Posted by Sara on Wednesday, August 22, 2007 at 8:27pm.

hmmm...I just can't seem to get it.
It looks like I got it right up to the volume of the metal point. Don't I have to divide the mass of the metal by the density of the water given before? (0.9970)? I guess I am having a problem with this which results in the wrong answer for the density because I have to use this number..right? The volume of the water is the mass of the water divided by the density of the water...That's what I did. I'm lost....
I do understand though what I did wrong with the first part. Do I have to use the volume of the flask, which was the volume of the water also to get the density of the Metal? Can you help me out?

Mass of stoppered Flask plus metal:
61.28g
Mass of stoppered Flask + Metal+ Water:
78.19g
Mass of metal:
61.28g - 37.34g= 23.94g
(Note that 37.34 is the mass of the stoppered Flask from before)
Mass of water:
78.19g - 61.28g=16.91g
Volume of water:
(16.91)/ (0.9970)=16.96cm^3
Volume of metal:
???????????
I did the following:
(23.94g)/(0.9970g/cm^3)= 24.01cm^3
then using this answer I need to caculate the Density of the Metal:
(23.94g)/(24.01cm^3)= 0.9970 g/cm^3

But why would the Density for water at 25*C, which was given, be the same as the density of the metal? Shouldn't it be different? So I came to the conclusion that in the end I must be doing something wrong because my answer is like walking around in circles...(The last two caculations), so I either don't really get the concept or I made a mistake from the get go...or I am using the wrong numbers, to calculate certain parts. so, this is were i need your help. I hope it's clearer whemn I show you exactly what I did.

Chemistry - ~christina~, Wednesday, August 22, 2007 at 8:37pm
Well...I corrected what I did wrong before and from that ...

to see what's happening with your calculations..

(23.94g)/(0.9970g/cm^3)= 24.01cm^3
then using this answer I need to caculate the Density of the Metal:
(23.94g)/(24.01cm^3)= 0.9970 g/cm^3
______________________________________
The density is NOT the same as water. so it would not be the mass of metal divided by density of water.
It would be however, what I later posted on the last last post.

Orig Vol- new Vol= 26.40cm^3 -16.96cm^3= 9.44cm^3 (vol of metal)

D of metal= Mass/Vol
23.94g/9.44cm^3= ____g/cm^3
- Chemistry - Sara, Wednesday, August 22, 2007 at 8:46pm
  Thank you so much...I would have never been able to figure that out. I would have never came up the idea of subtracting the new volume by the old volume...thank you for all your help!!
Chemistry - ~christina~, Wednesday, August 22, 2007 at 8:48pm
Your very welcome, I actually had a hard time figuring out that a few years back as well so I know what your speaking about =D

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