[FlySkyHigh22]

Whoo my first post! 
I searched before I posted, didn't see anything - sorry if I missed it!

So in my Chem II class we did the classic (or so it seems to me) "Analysis of Silver in an Alloy" experiment as an intro into the AP labs.  If you're not familiar with it, its basically taking a silver/copper metal whatchamajigger (i think we used old silver dimes) and after dissolving the copper/precipitating the silver with HNO3 (something like that happened ), we filtered out the solid AgCl precipitate with a filter crucible and aspirator setup.

Anyway.... we heated the filter crucible in a 100 mL beaker, covered it with watch glass and stuck it in an oven, weighed it, and later once we ran the solution through to get the AgCl precipitate out,  we heated it again, subtracted the weight of the EMPTY crucible, and got the mass of AgCl in the alloy.

Whoo thats a lot =P

So one of postlab questions says, "If the crucible containing the silver chloride is not cool when its mass is determined, will the calculated percent silver be too high or too low? Why?"

I cant find any reason that the temperature of the crucible would affect the mass that is read out on the scale, which would inadvertantly affect the % of pure silver.

  Thanks in Advance!

P.S. Sorry if any of the Chemistry jargon I used was wrong.... Still getting a hang of it XD

[enahs]

The scale is metal. Metal heats and contracts with temperature. Putting a hot crucible on the scale, the scale will heat and throw off the reading; and also uncalibrate the scale. And if it is a closed scale, the crucible can heat the air, PV=nRT, if you increase the temperature and keep the volume constant, the pressure must increase.

[FlySkyHigh22]

=D thanks that makes 10x more sense than what I was thinking.

I calculated .650 g Ag in the alloy, when we started it was only .610 g total.

XD Obviously someone in my group goofed or we were all just oblivious to something =P

[constant thinker]

=D thanks that makes 10x more sense than what I was thinking.

I calculated .650 g Ag in the alloy, when we started it was only .610 g total.

XD Obviously someone in my group goofed or we were all just oblivious to something =P

Or if your school is like mine, you have really, really bad equipment and maybe a couple stupid teachers/lab assistants that screwed something up along the way. 

[FlySkyHigh22]

i wish i could say that.

But my teacher is like a freaking genius; she graduated from high school when she was 16 and has like a gazillion masters degrees. (okay, maybe only one, but STILL)

and the scales are like $800, mucho sensitive lol.

Im thinking maybe we didn't get all the precipitate outta the beaker..

oh well whats done is done, she doesn't take off for percent error or anything 

[enahs]

You never get 100% yield anyway. And it is not always physical (loss of substance in transferring or bad equipment), but chemical reactions do not always give you 100% what the chemical equation says.

[FlySkyHigh22]

yes, but if i'm getting 106% of a silver-copper combination being silver, it just doesnt work.

i ended up with like .40 g of silver ALONE more than what I started with total lol!

oh well thanks everyone!