# Homework Help: Calculations 1

1. May 23, 2007

### Janka

Hello people...could u help me pls...coz i am rly stuck in these thing like calculations...i know all right answers but i am not too sure how to get them...please if somebody of us has a few minutes could u help me with that?
Thank you very much.

Azides are compounds of nitrogen , used mainly as detonators in explosives.
However , sodium azide , NaN3 , decomposes non-explosively on heating to release nitrogen gas. This provides a convenient method of obtaining pure nitrogen in the laboratory.

2NaN3 (s) ---> 2Na (l) + 3N2 (g)

1., A student prepared 1.80 dm3 of pure nitrogen in the laboratory by this
method.This gas volume was masured at room temperature and pressure (r.t.p).

(i) how many moles of nitrogen , N2 , did the student prepare?
- assume that 1 mole of gas molecule occupies 24.0 dm3 at r.t.p.

1 mol of gas molecule = 24.0 dm3

1.80 dm3 / 24 dm3 = 0.075 moles of nitrogen

(ii) What mass of sodium azide did the student heat?

2., After cooling , the student obtained 1.15 g of solid sodium.She then
carefully reacted this sodium water to form 25.0 cm3 of aqueous sodium
hydroxide:
2Na (s) + 2H2O (l) ---> 2NaOH (aq) + H2 (g)

Calculate the concentration , in mol dm-3 , of the aqueous sodium hydroxide.

Last edited: May 23, 2007
2. May 23, 2007

### cristo

Staff Emeritus
Welcome to PF. The rules state that you must show your work before you get help with homework or coursework questions. Furthermore, in future please post such questions in the homework forums.

3. May 23, 2007

### chemisttree

What is the relationship between the number of moles of sodium metal and sodium hydroxide? Same? Different?
Once you find the number of moles of NaOH, you should be able to determine molarity since you know the volume as well.