moles calculation question...?

Question

A 25.00g sample of sodium carbonate-10-water was heated in an oven to remove all its water of crrystallisation. Calculate:
a) moles of sodium carbonate-10-water present in the original sample

Note: How do I do this? I just worked out the molar mass of sodium carbonate-10-water (Na2CO3.10.H2O) which=286.15
What is the answer? Do I need to refer to the 25.00g sample size? What do I do?

b) mass of water driven off in the oven
c) mass of anhydrous sodium carbonate remaining after heating

Please help me and show working before the answer. Thankyou.

0.08736676568 moles
is that 0.087 moles (3 sig. figures) or do I do it to 5 sig. figures? If 5, is that 0.08736 or 0.08737 moles?

Answer 1

mass divided by molar mass
25.00/286.15=0.08736

Answer 2

I show you the maths but not the calcuations.

You have worked out the molar mass of Na2CO3.10.H2O

b) now you have to work out the molar mass of H2O

Then work out the no of moles in 25 g of Na2CO3.10.H2O

this is = 25 g/ 286.15 g/mol = x moles.

How work out the work of moles of H20 in the compound this equeals 10 x (x moles)

Then work out the weight of water 18 g/mol x 10 x (x moles)

= mass of water.

c) the renaming mass = mass of starting - water driven off.

remaining mass = 25g - mass of water driven off.

Answer 3

If the molecular weight is 286.15, then a 25.00 gram sample would be 0.087 moles.

If there are 0.087 moles of this salt, you would drive 0.87 moles of water off, or 15.66 grams. There will be 9.34 grams of sodium carbonate left.

Answer 4

oh my god.. go outside and play.