[shadesofemerald]

The Aim of the titration was to determine the percentage of nitrogen present as ammonium ions in lawn fertiliser

In a flask we added 20.00ml of 0.100M NaOH then put in 1.308g of lawn fertiliser. added water, mixed, added more deionised water until it reached 250ml.

We pipetted 20ml of the NaOH solution in each of the 3 conical flasks then heated all the conical flasks up till there was no ammonium gas left

Added an indicator then titrated with 0.100M HCl.
The average titre obtained was 11.18ml.

The manufacturer's claim was 12.3% of nitrogen present as ammonium ions so the answer is prob somewhere near there.

Some steps i've used then got stuck:(dunno if it's wrong or right tho)


Equations:
HCl + NaOH ----> NaCl + H2O

NH4+ + OH- --->NH3 + H2O

n(HCl): 0.100 x 0.01118= 0.001118 mol

n(NaOH): 0.100 x 0.020=0.002 mol (originally added)

n(NaOH)/n(HCl): 1/1

n(NaOH): 0.001118 mol

.


also i think one of the steps we had to do later was find the amount of mol NH+ in the 20ml then the amount of NH+ in the 250ml


thanks!

This post has been edited by dreami_babe: Today, 08:33 PM

[Arkcon]

So the actual question is?  You used the HCl titration to determine many moles of NaOH remained after the NH3 reaction, and you know how much NaOH you started with, can you determine moles NH3, and convert to percent?

[Lilly]

Hi
I got my planning exercise late!
I am doing the same planning exercise and i was wondering if any of you could help me. I am confused as to how to determine "suitable quantities of chemicals to use in titration and calculations to show how you worked out these quantities."
How do i work out the quantity of NaOH that will be suitable to titrate against 1.00moldm?

I reallly want to do well in this.
Please help me, I am a student in desperate need of help 

[Arkcon]

I am confused as to how to determine "suitable quantities of chemicals to use in titration and calculations to show how you worked out these quantities."

This is a common question for people to ask, and I didn't know, until now, that it was a lab preparation question to ask.  Basically, there are historical procedures for this sort of set up ... you'll be doing a titration, using an indicator that changes color, in an Erlenmeyer flask containing sample.  You don't want to fill it, when all reactions are done, because such a large volume won't change color all at once, and you'll find it hard to find the end point.  Also, if you're not done (haven't seen the color change for the endpoint) and the flask is full, there's nothing you can do, but dump it out and start over from the beginning, with less sample.  That happens sometimes, but usually only when you're told, "titrate this approx 1 M NaOH", ant it's really 2.5 M.

But they only way to know, is to look at your equipment, and see what physical size it is, and what volume you'll want to about 2/3 fill the flask, and try to calculate what sort of volume you should be working with.  But the lab setup should explain most of this to you.  Or you do one throw-away titration to just sort of see about what volumes you'll be working with.