Gravimetric analysis

[teletubbies_95]

1. In the Nelson book Unit 3 , do we need to memorize the different ways/pathways of gravimetric analysis(Chapter 3)?
2. In the Studyon book (Pg 42, Q1) , which states that :

Phosphorus is an important nutrient and is therefore present in many fertilizers it can be determined gravimetrically by carrying out a number of steps, eventually leading to it precipitation of insoluble Mg2P2O7. In one such analysis , a 14.298 g sample of fertilizer yielded 4.107g of Mg2P2O7 precipitate. Calculate the mass of phosphorus in the precipitate.

My thought process:
- i found the moles of precipitate and used the mole ratio to find out the mass of phosphorus.

I still got the question wrong. 0.8967g is the answer.

[huaxiadragon]

Interesting, I got the wrong answer as well.

I got

n(Mg2P2O7)=0.01845mol
n(P)=0.0369mol
m(P)=1.1439g

Used the same method you described. Sure you quoted the right initial values?

[teletubbies_95]

No. The figures are correct. I'm not even sure if the method is correct.

[huaxiadragon]

Pretty sure the method is correct, this is certainly weird. Perhaps the molecular formulae are wrong? Or incomplete reaction?

[teletubbies_95]

I attached the question .

I dunno if this breaches copyright or anything, but if it does , I'll delete it.

[huaxiadragon]

Well it's clear you made no mistakes in quoting the question.

Hmm....and Im pretty sure the method we used are correct. Perhaps the solution is incorrect? It does happen in textbooks

Here's what I got for the rest anyway.

a) 1.1439g
b) 8%
c) We assumed the all of the phosphorus in fertiliser precipitated