[legitbrit]

I did a lab the other day (gravimetric determination of chloride) and I'm really confused about the results. I'd heated two crucibles in the oven for half an hour, weighed them, and then did the lab. At the end of the lab, I put the product that I created into the crucibles, let them dry in the oven for two hours and weighed them a week later. One of the crucibles weighs more than before which is expected but one actually weighs LESS!

How is this possible?

[magician4]

(...)I'd heated two crucibles in the oven for half an hour, (...)
(...) let them dry in the oven for two hours (...)
(...) one actually weighs LESS! (...)

to me, the answer seems obvious, doesn't it?


regards

Ingo

[legitbrit]

Sorry, what I meant was that the crucible without the product weighs less than when I put product in.

[magician4]

Sorry, what I meant was that the crucible without the product weighs less than when I put product in.

this seems even more obvious to me, as a "product" usually has a weight in its own right, which usually tends to add up with the weight of the crucible when put together on scales

or what, exactly, seems to be the problem? am I missing something here?


regards

Ingo

[curiouscat]

Moisture. Crucible wasn't fully dry.

From what I remember you keep drying n weighing at  30 minute intervals until succesive weights come the same.

Or

Bad weighing scale.

[Borek]

and weighed them a week later

Apart from every possible operator error - you should weight them immediately after drying and cooling, you shouldn't wait a week with weighting.

But I would not look for any other explanation than the error in weighting and/or writing down the result. Wild speculation won't change anything.

[legitbrit]

Sorry, what I meant was that the crucible without the product weighs less than when I put product in.

this seems even more obvious to me, as a "product" usually has a weight in its own right, which usually tends to add up with the weight of the crucible when put together on scales

or what, exactly, seems to be the problem? am I missing something here?


regards

Ingo

I'm recovering from surgery and I'm still a bit loopy so sorry. The crucible WITHOUT product weighs more than when I added product to it. The product has weight of its own. Also, I waited a week to weigh it because I had to. That's just the way that lab was set up guys. My professor wouldn't have it any other way. And I know that speculation won't change anything, but I have to explain this in my lab report and I'm truly puzzled. Thanks

[Corribus]

Also, I waited a week to weigh it because I had to. That's just the way that lab was set up guys. My professor wouldn't have it any other way.

Well I think you have your answer.  Ceramic is a porous material and can absorb a lot of water over a week, particularly if there's been a humid day.