A student tests the absorbance of a solution of nickel sulfate and cobalt chloride from 400 to 700 nm. The nickel sulfate had a peak at 405 nm and the cobalt chloride had a peak at 512 nm. Write 3–4 sentences to describe how an absorbance spectrum is obtained and why there are differences between the two molecules.

Question

anonymous · Answer

@Somy @Luigi0210

anonymous · Answer

Write 3–5 sentences to describe how the actual concentrations of each sample of nickel sulfate can be determined from the spectraphotometric data.

luigi0210 · Answer

@Somy 's got it ;P

anonymous · Answer

@Luigi0210 ok. @Somy @Tech1 I don't even know where to start haha

anonymous · Answer

@Abmon98

anonymous · Answer

@Somy

aaronq · Answer

An absorbance spectrum is acquired by scanning taking abs measurements at every wavelength in the range.

There are differences - for the obvious reason - that they're different compounds which will have electrons that are excited at different energies. This can be expanded on with crystal (or ligand) field theory if you've learnt about that.

anonymous · Answer

ok and then Write 3-5 sentences to describe how the actual concentrations of each sample of nickel sulfate can be determined from the spectraphotometric data. @aaronq I have no idea what this means lol

aaronq · Answer

in a cuvette (small vile of known dimensions) you put a known volume of a sample.

You select the wavelength at which the substance has the highest abs (this is why you need the spectrum) and take readings. 

then use the Beer-Lambert law: $ Abs=\epsilon*l*c$

$\epsilon$=molar extiction coefficient
l = path length (of cuvette)
c= concentration (in molarity)

aaronq · Answer

You also need to prepare your sample and blanks to calibrate the instrument, but i dont think you need to talk about that here.

anonymous · Answer

but @aaronq what is the actual process? just take down the measurements and plug it into the equation?

aaronq · Answer

yes

aaronq · Answer

if you need to describe the physical principles of the instrument, thats another story.

anonymous · Answer

oh ok I was just overthinking it i guess

anonymous · Answer

thank you!

aaronq · Answer

no problem !