calculation help pls!! (1 Viewer)

[lozabella]

we just did this sulfate fertliser prac thing.....and we have this calc question at the end of it and i've tried four different ways and have gotten four different answers...none of which are sounding right so i'm stuck!! some help would be very greatly appreciated!!
here's the question:
If the fertiliser contains 10.1% potassium, calculate the % of Nitrogen in the fertiliser( assuming all the potassium is present as Potassium Sulfate and all the Nitrogen is present has Ammonium Sulfate and no other source of sulfate is present. There was some question above it and we got that there was 67.3% Sulfate present in the fertiliser mix which was 0.0086118 moles.

 

[Jumbo Cactuar]

whoa! I would have got to this sooner...

Ok here goes...

Mass of fertiliser = ___? = x

Mass of K2SO4 in fertiliser = x * 0.101

Molar mass of K2SO4 = 16*4 + 2*39.1 + 32.07 = 174.27 g/mol

Amount of K2SO4 in fertiliser = ( x * 0.101 ) / 174.27 mol

Amount of S04 2- in fertiliser = 8.6118 *10^-3 mol

Amount of (NH3)2SO4 in fertiliser = 8.6118 *10^-3 - ( x * 0.101 ) / 174.27 mol

Molar mass of (NH3)2SO4 = 6*1.008+2*14.01+16*4+32.07 = 130.14 g/mol

Mass of (NH3)2SO4 in fertiliser = (8.6118 *10^-3 - ( x * 0.101 ) / 174.27) * 130.14 g

Percentage (NH3)2SO4 in fertiliser = (8.6118 *10^-3 - ( x * 0.101 ) / 174.27) * 130.14 * 100/x %
= 0.6431/x - 7.5424 % (x > 80mg)