Chemistry question, I think it has to do with empirical formula?

Question

Here's the problem:

Washing soda, is a hydrate, which means that a certain number of water molecules are included in the solid structure. It's formula can be written as Na2CO3 * XH2O, where X is the number of moles of H2O per mole of Na2CO3. When a 2.558 gram sample of washing soda is heated at 25 degrees celsiusous, all the water of the hydration is lost leaving 0.948 grams of Na2CO3. What is the value of X?

please help me :(

my chem teacher told me that I did these kinds of problems last year, but I didn't and she won't tell me how to do it :(

Answer 1

Some helpful teacher. Here's how:

The ratio of the weight of water to the weight of sodium carbonate is equal to the ratio of their molecular masses......

2.558 - 0.948 = 1.61

Na2CO3 = 46+12+48 =106

XH2O = 18X

1.61/0.948 = 18X/106

18X = 180

X = 10

The mineral natron, is natural sodium carbonate decahydrate