Need help with Chemistry assignment :)

[that_guy]

Heyy folks, im looking for a source or info on what ammonium hydroxide does in spectrophotometry in finding concentration of copper II sulfate. need info fast as the assignments due Wednesday!! if needed ill scan the experiment sheet and email :D

cheers,
tony

[OICURMT]

I don't know about Ammonium Hydroxide, but any Copper Sulphate is a covalent copper, thus would emit in the blue region of the spectrum. Note that there should be adsorption lines in the 432nm & 460nm range. I'd suggest you look into interference effects of hydroxides via adsorption lines.

Is your assignment for an experiment that you are performing?

If it's a titration experiment then hydroxide would probably be used as an agent to indicate the presence of copper (not sure which kind though, cupric (covalent) or cuprous (monolavent)).

It's been decades since I've studied Chemistry. Alas, all my Chemistry books are in storage back in the USA, so I'm going from one of my books here, The Spectroscope and Gemmology, Anderson & Payne (1998) and extrapolating some possibilities.

OIC!

[marki]

Tony it would help if you told us the type of spectrophotometry i.e. UV, IR or visable for colorimetry. Ammoium hydroxide will form as soon as you mix NH3 with water. Normally the OH ion will form a sky blue solid with the Cu2+ ion (not much use for visable analysis) but in this case if it is a concentrated solution of NH4OH a deep blue/purple complex ion will form ([Cu(NH3)6]2+). I can see no real use for ammonium hydroxide to be added to visable spectrum analysis as it is relatively simple to determine the the concentration of CuSO4 using a single or double beam spectrophotometer. You just need a calibration curve and you are off. With IR you have to make little disks where you mix your sample with powdered KBr and put it in a press to squash them together (a real pain as the disks are very fragile) but this is only good for composition and structure. If you use liquids to determine conc in IR spec you must use a cell (cuvettes) made of an insoluble salts like AgCl as glass as most materials absorb and emit IR frequencies and this will muck up your accuracy. I still cannot think of a reason to use ammonium hydroxide.

Mark

[that_guy]

hi mark :) sorry, its a visible light to measure the percent of transmittance of light...

cheers,
tony

[that_guy]

thanks OIC!! LOL... its for a write up report for an experiment i performed... :D

[marki]

Still cant think of a reason Tony, where did you get your info on needing NH4OH from??? All sortd of things can affect the accuracy of your reading e.g. dirty or scratched cuvette, sediment in the sample etc. Another biggie is the absortion by the solvent itself even if it was colourless. The only time I can remember using an ammonium compound (ammonium vandomolybdate) was to determine a phosphate concentration.

Mark

[that_guy]

the teacher gave us a sheet in which we followed to the line when we were doing the experiment... it said to add 2 drops of ammonium hydroxide in to the solution before putting it in to the spectrophotometer... :shrug:

[marki]

Okay Tony, there are only two things I can think of.

1. Depending on how they got the CuSO4, a slight adjustment in pH may be needed. e.g. they may have used conc sulfuric to dissolve the solid copper :shrug:.

2. They want you to analyse ammonical copper ([Cu(NH3)6]2+) for some reason. Do you know how strong the ammonium solution was?

Mark

[that_guy]

the ammonia was 14.8M mark

[AstralTraveller]

My first guess was that you need to ensure that all the copper is in the 2+ oxidation state. After looking on Wiki I'm pretty sure you have made Schweizer's reagent aka tetraamminediaquacopper dihydroxide, which will ensure all the Cu is as Cu II and will give very good absorbance. Was the result a deep azure blue?

See

http://en.wikipedia.org/wiki/Ammonia#Ammonia_as_a_ligand
http://en.wikipedia.org/wiki/Schweizer%27s_reagent

Don't worry too much about the term 'ligand' and 'sigma donor' (σ-donor), they are both upper uni topics.

If you can get a hold of 'Standard Methods for the Examination of Water and Wastewater' it should cover it in detail.



Cu(NH3)4(H2O)2](OH)2

BTW what you want to measure isn't transmission, it is absorbance. If PO = (power of light source) and p = (power received by detector) then transmission = p/PO but absorbance = -log(base 10) (PO/p). The point is that you must express the light loss as absorbance so you can use the Beer-Lamberts Law to calculate the concentration.

http://en.wikipedia.org/wiki/Ultraviolet%E2%80%93visible_spectro scopy

ps As an undergrad the alternative formulation of Beer-Lamberts Law was "bugger spectroscopy, lets go to the bar".

[marki]

Yes agree David. Tony has since indicated that the copper sulfate solution was very dilute (0.05 M) so a couple of drops of 14 M would probably do the trick.

Mark

[OICURMT]

Geezzz... I'm glad I didn't get too involved in this one... would have been left behind "in a heartbeat"... :lol:

[that_guy]

yep mark, 2 drops to be exact :P asked the teacher today and she told me the same thing :D cheers all!! yous all legends!! :lol:


cheers,
tony

[Suzy]

My head hurts after reading this. :confuse2:
:lol:

[astroron]

:hi:Tony, I didn't even try to read it as it is Waaaaay above my understanding :rolleyes:
Congratulations anyway:thumbsup:
Cheers

[that_guy]

Its okay guys... i just go with the flow :lol:

[AstralTraveller]

Tony, chemistry is where it's at. A reasonable chemistry knowledge is vital in many fields of work - medical, environmental, materials, earth science, astronomy to name a few. I think the assignment you did is quite advanced for high school; titrations was about as far as we went at school.

A shockingly high percentage of students enrolling in chemistry at uni have not done any high school chemistry and virtually no geology graduates who want to do geochemistry have done much chemistry at uni. In both cases they are well behind the 8-ball and have a lot of catching up to do. The knowledge you are gaining now will stand you in good stead for the rest of you life. (And IMHO it's actually a lot of fun.)

[rowena]

oK what highschool can afford a spectrophotometer?! I know I graduated nearly 20 yrs ago from highschool and we didn't have them back then! :\

2H + 02 -> 2H20 was the kinda stuff we did most days, and then getting into electrons, electron swapping and all that fun stuff.

[el_draco]

I agree totally. Chemistry is the glue for the universe and I am horrified by how how little students know. Half the problem is that it requires that novel thing called study. 30 minute grabs once a fortnight is a waste of time...

[rowena]

I started a degree in chemistry at uni. I did chemistry, phsyics, maths 1 and biology at highschool. What failed me was my lack of maths.. where i needed maths 2... or maths C what it used to be called..

I dont know how people can go try and do a chem degree without having done it at highschool... u have all your basics from highschool for uni! :\

[jenchris]

Odd that, I did titration at grammar school when I was 15.
44 years ago