CHEM URGENT!!
posted by matt .
If a cube with edges of 1.000 cm weighs 25.68 g, what would the mass of a cube
of the same material with sides 2.63 cm in length be?

the ratio of volumes is the cube of the length ratio:
(2.63)^3 = 18.19
18.19 * 25.68 = 467.2 g 
Damon has worked this problem as a math problem. If you wish to look at it from a chemistry perspective (that's the title of your post); calculate density of the first one.
volume = 1 cm x 1 cm x 1 cm = 1 cc.
density = mass/volume = 25.68/1 cc = 25.68 g/cc.
Second cube.
volume = 2.63cm x 2.63 cm x 2.63 cm = 18.19 cc
mass = volume x density = 18.19 g x 25.68 g/cc = 467.2 grams.
By the way, there aren't many things with a density of 26 g/cc. 
DrBob makes an interesting point: "By the way, there aren't many things with a density of 26 g/cc."
The two densest things I could find were uranium (18.9 g/cc and plutonium (19.8 g/cc)
I hope you aren't planning to make a bomb.