Quick Gravimetric Question

[asiandee]

It asks me to find the average mass of the precipitate (AgCl) with 5 weighings and then find the mole of NaCl. The five weighings were:
1. 1.183g
2. 1.137g
3. 1.109g
4. 1.110g
5. 1.108g
My question is, why do you have to use concordant results in this question to find the mole of NaCl, I thought the whole point of gravimetric was to eliminate all the water in the precipitate and then use that mass to find the mole :S.

[Somye]

That is what you're doing!

The weights above are what occurs when you heat your substance to constant mass (get rid of water)
Therefore, your last 3 masses show that point, as the difference between them becomes minimal

So use the average of those last three masses, and calculate mol of AgCl, and work from there

[asiandee]

Wouldn't the last result be more accurate? Because that would be the mass with the least amount of water :S