# Homework Help: Chemistry Mole calculations

1. Sep 17, 2010

### Hockeystar

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

Determine the number of moles of Nitrogen atoms in a sample of C7H5(NO2)3 that has the same number of oxygen atoms as 12.6 grams of sugar.

2. Relevant equations
Mole calculations

3. The attempt at a solution

First find the amount of moles of Oxygen in sugar. Multiply 12.6g by 96grams O/ 180grams sugar to get 6.72grams of sugar. The divide 6.72grams by 16 to get 0.42 moles of Oxygen. Then I'm struggling at the next part. To get the same amount of moles of Nitrogen shouldn't I just divide 0.42 by 3 to get 0.14? 0.14 was not the correct response on mastering chem.

2. Sep 17, 2010

### zorro

Determine the number of moles of Nitrogen atoms in a sample of C7H5(NO2)3 that has the same number of oxygen atoms as 12.6 grams of sugar.

First calculate the no. of oxygen atoms in sugar
moles of sugar = 12.6/342
no. of O atoms= 12.6/342 x 11x N where N is avogadro number

Let the mass of the compound given be m
moles of this compound= m/227
no of O atoms= 6 x m/227 x N

equate and get m,
I got it as 15.3 g
Now moles of nitrogen atoms = 15.3/227 x 3

3. Sep 17, 2010

### Hockeystar

Isn't the molar mass of sugar 180 g/mole not 342?

4. Sep 17, 2010

### Staff: Mentor

What sugar? Ribose? Arabinose? Xylose? Gulose? Lyxose? Psicose? Fructose? Sorbose? Tagatose? Allose? Altrose? Glucose? Mannose? Idose? Galactose? Talose? Sucrose? Lactose? Maltose? Trehalose? Turanose? Cellobiose? Ribulose?

5. Sep 17, 2010

### Hockeystar

My bad, I meant glucose. Thanks for showing the steps to solving the problem.

6. Sep 17, 2010

### zorro

Here in this question 'sugar' can be assumed as sucrose as nothing is mentioned about it.