[PointlessDirection]

It has been a minute(10 years) since I have had to do this, but how would you find the concentration of Nitrogen in a standard made from NH₄Cl? For example, if I weigh 3.8 g of NH₄Cl and dilute to 1000 mL it is supposed to have a concentration of 1 mg of N/mL, but I cannot remember the make to make sure this is correct.

[Corribus]

How many assumptions are you willing to make? There are a number of tests for ammonium ion concentration, so if you are willing to assume that mole ratio of nitrogen to ammonium is exactly 1:4, then you could use one of those. If you need a direct measurement of nitrogen, that's harder because nitrogen is everywhere.... including dissolved in your solvent. You could do CHNX/CHNS (combustion) analysis, but you'd need to remove your solvent first and then back-determine concentration using the volume of solvent you removed. But that'd be kind of silly... because why did you add the solvent in the first place, then.

https://en.wikipedia.org/wiki/CHN_analyzer

[chenbeier]

I think he will only know to calculated.

Calculate the moles of 3,8 g ammonium chloride using molecular mass this equal of the moles of N. Then convert back to the mass by using molecular mass of N.

[Corribus]

Oh. Well I feel kinda silly now.

[MNIO]

how's your dimensional analysis?

   3.8g NH4Cl        14.01g N           1000mg N
 --------------- x ------------------ x ------------- = 1.0 mg N / mL
     1000mL        53.491g NH4Cl         1g N

on the left is what you started with
the middle fraction is the unit factor made from mass fraction N in NH4Cl
the right fraction is the unit factor made from 1000mg = 1g
enter the calcs as 3.8/1000*14.01/53.491*1000 = . or better yet... 3.8*14.01/53.491 =
round to 2 sig figs
note what's canceling.. g NH4Cl / g NH4Cl.. g N / g N.. leaving mg N / mL solution

   3.8g NH4Cl        14.01g N           1000mg N
 --------------- x ------------------ x ------------- = 1.0 mg N / mL
     1000mL        53.491g NH4Cl         1g N