# Homework Help: What is the percentage of ammonia in the sample?

1. Jan 28, 2010

### tag16

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

Ammoniacal nitrogen can be determined by treatment of the sample with chloroplatinic acid; the product is slightly soluble ammonium chloroplatinate: H2PtCl6 + 2NH4 --> (NH4)2PtCl6 + 2H

The precipitate decomposes on ignition, yielding metallic platinum and gaseous products:
(NH4)2PtCl6 --> Pt(s) + 2Cl2(g) + 2NH3(g) + 2HCl(g)

Calculate the percentage of ammonia in a sample if 0.2115g gave rise to 0.4693g of platinum.
2. Relevant equations

3. The attempt at a solution

0.4693(1/(14+1+1+1))= 0.0276
0.0276(2)(159)= 8.778
8.778/0.2115= 41.5%

did I do this right? The back of my chemistry book says that the answer should be 38.74% NH3, so if this is correct how would you arrive at this answer?

2. Jan 29, 2010

### Lok

Did you use NH4 or NH3 as ammonia is NH3. Might be a mistake there as for Molecular mass 17 the result is the one in the book.

3. Jan 29, 2010

### Staff: Mentor

Please elaborate, I have no idea what you did. You started dividing mass of platinum by the molar mass of ammonia, next you multiplied the result by 2 (stoichiometric coeffcient) and by molar mass of platinum (with digits reversed to make it harder to guess what you did). From what I understand at this stage your result is in rather unexpected units:

$$\frac {(g_{Pt})^2 (mol_{NH_3})^2} {g_{NH_3} (mol_{Pt})^2}$$

I doubt that's what you wanted to do, from the last operation seems like you think at this stage you have mass of ammonia multiplied by 100.