Open Investigation: Testing Fertiliser (1 Viewer)

[iluvbyrnsie]

Does anyone have any information on the experiment testing the sulfate content in lawn fertiliser?? I have to design an experiment and some of the apparatus and methods are confusing me.

 

[ND]

Which part is confusing you?

 

[iluvbyrnsie]

Why do you need to use excess Barium Sulfate, and how can you test to see if all of it has reacted? And is filter paper effective enough to filter the hydorcholic acid through the fertiliser

 

[jm1234567890]

you use excess cause it is dificult to see if all of it has reacted and the excess wont affect the procedure.

filter paper is not enough, you need a sintered glass filter with vacuum pump. The precipitate is VERY fine

 

[jims]

BaSO4 is what you're going to be precipitating. u use excess BaCl or something which is soluble to react with the SO4 in the fertiliser to form the BaSO4. you cant really do any test to see if it has all reacted which is why you use excess BaCl.

i dont think its possible to filter HCl nor why you would need to for this prac.

if u want to filter the BaSO4 (which you do because thats what ur trying to analyse), you should use a sintered glass funnel because filter paper isnt fine enough to collect the precipitate.

u can improve the experiment by warming the BaCl and fertiliser solution and pouring the BaCl in slowly with constant stirring to create larger precipitate particles which will be easier to filter.

 

[parry]

or you can do the titration method, but i dont like it as much as this one

 

[inasero]

yeah i also have a question pertaining to this experiment...what is the purpose of adding HCl of a known concentration (according to MacMillan)? isn't is only meant to dissolve all of the fertiliser?

 

[Constip8edSkunk]

u dun need a known concentration... it prevents precipitation of PO4 3- by shifting the equilibrium towards HPO42- and H2PO4 - i think

 

[inasero]

ehheh u thought wrong

it prevents precipitation of PO4 3- by shifting the equilibrium towards HPO42- and H2PO4 - i think

its only there to dissolve sulfate afaik

but thanks anyhows
by the way based on what you've seen so far what raw mark dya reckon we will need to get band 6 in maths ext 2 this yr?

 

[mercury]

you want concentrated HCl for two main reaons:

1. to ensure that none of (at least minimal) other barium ppt (eg. BaCO3) is produced.

H2O + CO2 <=> H+ + HCO3 -
HCO3 - <=> H+ + CO3 2-
BaCO3 (s) <=> Ba2+ + CO3 2-
to explain it in a simple sense, js use Le Chatelier.

2. coz BaSO4 crystals are puny... it's hard to filter. agar gel can coagulate the particles better, but also concentrated acid like HCl is adsorbed onto BaSO4 surface during precipitating. This somehow makes the surface slightly charged so the microcrystals get attracted to each other and coagulate better.

 

[phenol]

other way around merc BaSO4 absorbs the Cl- onto its surface via some surface effect

other bits all cool

 

[mercury]

righteo *salute*

 

[ND]

In the procedure i have for this (i didn't actually do the prac) it says to boil the water (after adding the HCl), and to add the BaCl2 while it's boiling, can anyone tell me why this is?

 

[toknblackguy]

boiling?
most probably to aid in the coagulation of BaSO4 sulfate crystals

 

[iluvbyrnsie]

It is suggested that you boil the solution while adding the barium chloride in order to achieve larger particles of sulfate precipitate which can then be collected by the filter paper. Our reacher suggested however, that running the solutions (in the beakers/conical flask) under hot water, is sufficient enough in heating the solutions.