# Homework Help: Calculating Mass Of Sulphur

1. Nov 15, 2015

### Sace Ver

1. The problem statement, all variables and given/known data

Determine the mass of all the sulphur atoms in 71g of Na2SO4?

2. Relevant equations

Not sure

3. The attempt at a solution

Do I divide 71 by 7 because 2+1+4=7?

And then would I multiply 1 by the number I get?

2. Nov 15, 2015

### MexChemE

There are 32 grams of sulfur in a mole of Na2SO4. Calculate the molar mass of sodium sulfate and then use a simple rule of three to calculate what you need.

3. Nov 15, 2015

### SteamKing

Staff Emeritus
And then would I multiply 1 by the number I get?[/QUOTE]

Why? Does an atom of Na weigh the same as an atom of S and the same as an atom of O?

You're still apparently hazy on the concept of what a mole is and how to calculate the weight, in grams, of one mole of a substance, given its chemical formula.

If you have 1 mole of Na2SO4, how many moles of S will there be? For any amount of this substance which is less than the weight of 1 mole, simply ratio the amount of the substance you have to the weight of one mole to determine the amount of S in 71 g of the substance.

This is a very simple concept to grasp, but you must study it carefully.

4. Nov 20, 2015

### Sace Ver

Would it be 16g of sulphur?

5. Nov 20, 2015

### SteamKing

Staff Emeritus
MexChemE was correct in that you need to calculate the molar mass of Na2SO4 in order to find the mass of S contained in 71 g of the original substance.

This 'Rule of Three' which was mentioned is not at all clear.

6. Nov 21, 2015

### MexChemE

Oh, sorry. I meant this.
$$\frac{32 \ \mathrm{g \ S}}{142 \ \mathrm{g \ Na_2SO_4}} = \frac{x}{71 \ \mathrm{g \ Na_2SO_4}}$$