Calculating Copper Density: Is My Bar Pure?

[CuriousMister]

I recently bought a 1-pound .999 fine copper bar. I was curious to know how closely the density of my bar was with the actual density of copper (about 8.96 g/cc). My bar measured 1 pound .5 oz (467.76 g). I calculated the volume two ways, water displacement and measurement; the volume is 48cc. Therefore the density is calculated as 9.745 g/cc (467.76/48). Why is my bar denser than the actual density of copper. It makes me think the bar isn't pure, but is mixed with another denser metal. Any thoughts?

 

[mfb]

8% deviation.
How precisely did you measure the volume?

Can you measure the apparent weight of the copper bar when submerged in water and held up by a rope?

 

[CuriousMister]

There probably is significant error in volume calculation. If the volume was 52 mL instead of 48 mL, the density would be very close to the actual density. On second thought, my volume displacement measurement was probably less than the least measurable quantity on the graduated cylinder I used.

 

[aikismos]

Oooh. Fun.

First of all, please note that you can only claim that your density is ## 9.7 \frac{g}{c^3} ## on account that your volume only has two significant figures.
I'd have to agree that it's like an error in volumetric evaluation. It's pretty difficult to measure the volume of physical objects. Is the bar a perfect rectangular solid, and what was the resolution of instrument to measure length? Using fluid displacement would be the way to go, but even then do you have a flask that can measure extremely fine gradations in the change of volume? Putting it in a standard measuring cup and estimating would easily create a deviation. Describe how you arrived at your volumetric measure.