Volumetric Determination of Nitrogen Content in Fertiliser

[vexx]

Hi,

This may be good practice for peoples, but i'm just wanting verification as i think i know what to do, but wanting to verify by seeing how someone else would do it
It's similar to my SAC question so i won't to make sure i know the exact correct procedure, just in case !

Summary:
1.3g of fertiliser-->diluted with water to 250ml--->20ml aliquot taken and put into a conical flask--->20ml of 0.100 M Sodium Hydroxide solution put in flask also--> Add +50ml of de-ionised water ---> Boil until all ammonia is gone (tested with litmus paper) --> cool the flask---> fill a burette with 0.100 M HCl --> add methyl red indicator ---> titrate with the HCl until endpoint is reached --> repeated with an average titre of 18.50ml

Calculate the %w/w of nitrogen in the fertiliser sample:

Thanks,

Vexx.

[hhland]

Just remember to place 1.3g of fertiliser and add water half way and mix till all the fertiliser dissolves before filling up to the 250ml mark. Im not so sure about the rest since I didnt do this prac...

[Blakhitman]

LOL...looks familiar.

Anyway, the way I'd go about it is:

find n(HCl) that reacted with NaOH, hence find (with mole ratios) n(NaOH) that DIDNT react with NH4 or excess NaOH, then minus excess n(NaOH) from original n(NaOH) to find the n(NaOH) that DID react with NH4, then use mole ratios to find n(NH4)...

the rest is simple...

[coletrain]

im pretty sure that our school is having a SAC on this, this week

[Blakhitman]

yeah ours is actually the exact same as Vexx mentioned. 1.3g too rofl.

[vexx]

LOL, i think we all have the same sac...

LOL...looks familiar.

Anyway, the way I'd go about it is:

find n(HCl) that reacted with NaOH, hence find (with mole ratios) n(NaOH) that DIDNT react with NH4 or excess NaOH, then minus excess n(NaOH) from original n(NaOH) to find the n(NaOH) that DID react with NH4, then use mole ratios to find n(NH4)...

the rest is simple...

oooh that's what i did but it seemed too simple, like the last sac .___.
thanks:)

i got 2.019% for this data i just gave, the sac won't be that small.

[Blakhitman]

If I remember correctly, the % of Nitrogen in the fertiliser we're using as shown on the box was 1.92% so that looks darn close....

EDIT: LOL just realised you made up the Data...

The % of Sulphate we had to find in the first part of the prac using gravimetric analysis in the fertiliser was almost 3 times what was mentioned on the box....but most the class got similar results, so I stopped freaking out lol.

[vexx]

edit, yeah heaps of people in my class got huge results for that like 32%+, whilst i got 13.8% which ended up being the right one haha.
don't want to scare you

If I remember correctly, the % of Nitrogen in the fertiliser we're using as shown on the box was 1.92% so that looks darn close....

oh hahah, are you serious.
i just made up a random titre of 18.50ml- i thought a much smaller titre would be used and there would be heaps more nitrogen in fertiliser. how silly, i just tried it again with a titre of 10.87ml and got 12.2%, i thought that'd be more correct o-O.

[Blakhitman]

re-read post :p

[Blakhitman]

Did you do the sac yet? if you did, how was the result compared to % on the packet of Nitrogen (as ammonium)??

we did ours yesterday, I got 19% (as opposed to 1.2%)....but the Total nitrogen in the fertiliser is 21% so I said that there is the chance that it included other ammonia compounds, because what we were asked to find was Nitrogen as ammonium, most of class got similar result, and this is the only explanation I could give. you think it sounds reasonable??

[vexx]

Did you do the sac yet? if you did, how was the result compared to % on the packet of Nitrogen (as ammonium)??

we did ours yesterday, I got 19% (as opposed to 1.2%)....but the Total nitrogen in the fertiliser is 21% so I said that there is the chance that it included other ammonia compounds, because what we were asked to find was Nitrogen as ammonium, most of class got similar result, and this is the only explanation I could give. you think it sounds reasonable??

i think so, basically you were asked why your result was different?
you could have perhaps mentioned titration errors. but i don't know if i get your question haha.

and yeah i did it on monday, i got 1.2% higher then the one on the packet. everyone had different results due to a) quite a few people don't understand how to work this out, and b) everyone had different titre averages.

[Blakhitman]

Ok, lol I just read what I wrote...it confused me so don't worry :p

what was the % on the packet?

[vexx]

Ok, lol I just read what I wrote...it confused me so don't worry :p

what was the % on the packet?

haha. i think all schools would use different fertiliser.
ours was 12%.

[Blakhitman]

yeah, I was thinking maybe our teacher read it wrong, because the whole class got way higher than 1.2%.

oh well, I'll just account for the differences and hope for the best!

we got redox titration next, determining iron content in the fertiliser using potassium permanganate...you the same??

[vexx]

yeah, I was thinking maybe our teacher read it wrong, because the whole class got way higher than 1.2%.

oh well, I'll just account for the differences and hope for the best!

we got redox titration next, determining iron content in the fertiliser using potassium permanganate...you the same??

we haven't found out yet. i think we get told tomorrow. probably haha.