Colorimetric determination of Iron Flashcards
what is one method for the determination of iron
based on the formation of the orange-red Iron(II)-orthophenanthroline complex
what is Iron(II)-orthophenanthroline often abbreviated to
“ferroin” with the molecule formula:
is orthophenanthroline an acid or base
base
what happens when orthophenanthroline is added to an acidic solution and WHY
it becomes pronated and giving up the phH+ ion because it is a BASE
what is the best pH for the formation of the Iron(II)-orthophenanthroline complex
3.5
why is a pH of 3.5 the best for the formation of the complex
because at this pH it is the best to PREVENT the formation of various iron salts (phosphates)
what is the importance of the hydroxylamine hydrochloride in this experiment
it is a reducing agent that prevents the iron (II) from being oxidized to iron (III) during the experiment
what is a benefit once the Iron(II)-orthophenanthroline complex forms
it holds it colour for a long period of time which allows for the determination of the concentration of the Iron(II)-orthophenanthroline complex
describe how colour is seen in the visible wavelength section of the electromagnetic spectrum
it “removes” them from the spectrum and the solution will appear to be a mixture of the colours NOT absorbed
what colours does the Iron(II)-orthophenanthroline complex absorb
green and blue light
what colour does the Iron(II)-orthophenanthroline complex appear
red-orange
what was the specific wavelength the Iron(II)-orthophenanthroline complex was measured at
508 nm (a shade of GREEN)
what is transmittance (T)
the relationship between the power of the original beam (Po) of light and the emerging beam of light/the remaining power after the beam has passed through the sample (P)
is the relationship between transmittance and solution concentration direct or indirect
not direct
is the relationship between absorbance and solution concentration direct or indirect
direct
what is the equation for Beer’s Law
A=abc
what do the different variables in Beer’s law indicate
A=abc
A is absorbance
a is absorptivity constant
b is cell width
c is the concentration
what is the fundamental law governing the absorption of all types of electromagnetic radiation
A=abc
(Beer’s law)
does Beer’s law only apply to solutions
NO - applies to solids and gases as well
why is a blank used in spectrophotomerty
to correct for a loss in beam power at each interface due to reflection and scattering by larger molecules
was it okay to use tap water, yes or no>
NO - tap water contains dissolved iron and other ions which messes with the results
how much of the iron salt solution was put into a 50 mL beaker
about 40 mL
what does iron salt refer to
Iron (II) ammonium sulfate hexahydrate
how were the 5 different solutions and blank created in this experiment
blank
- 0mL of iron salt
- 2.0 mL 10% hydroxylamine hydrochloride
- 3mL Orthophenanthroline
solution 1
- 1 mL iron salt
- 2.0 mL 10% hydroxylamine hydrochloride
- 3mL Orthophenanthroline
solution 2
- 2 mL iron salt
- 2.0 mL 10% hydroxylamine hydrochloride
- 3mL Orthophenanthroline
solution 3
- 3 mL iron salt
- 2.0 mL 10% hydroxylamine hydrochloride
- 3mL Orthophenanthroline
solution 4
- 5 mL iron salt
- 2.0 mL 10% hydroxylamine hydrochloride
- 3mL Orthophenanthroline
solution 5
- 10 mL iron salt
- 2.0 mL 10% hydroxylamine hydrochloride
- 3mL Orthophenanthroline
what can 1ppm be considered in water
1mg/L
what were the axes of the calibration curve
x was concentration of Fe2+ in ppm
y was the absorbance values
what are some health and safety reminders for HCl
- causes severe burns
- vapours irritate respiratory system and eyes
how to prepare 26mL 6 M HCl from 12 M HCl
combine 13 mL of RO water with 13mL of the 12 M HCl
how was solution A prepared
- 1 tablet of the iron was placed in 26 mL of 6 M HCl in a 100 mL beaker
- it was heated to a slow boil and stirred for about 15 minutes
- after it was diluted with about 10 mL of RO water
- filtered through filter paper into a 100 mL volumetric flask
- diluted to the mark with RO water
how was Solution B formed
- 5 mL of solution A was pipet into a clean 100 mL volumetric flask
- diluted to the mark with RO water
how was the number of sodium citrate drops determined
- pipet 10 mL of solution B into a smaller beaker and test pH
- add sodium citrate drops until the pH was about 3.5
how was solution c prepared
- pipet 10mL of solution B into a 100 mL volumetric flask
- add the required drops of sodium citrate for a pH of 3.5
- add 2.0 mL 10% hydroxylamine hydrochloride
- add 3mL Orthophenanthroline
- dilute to the mark with RO water
how was the blank for solution C prepared
- 2.0 mL 10% hydroxylamine hydrochloride
- 3mL Orthophenanthroline
- required drops of sodium citrate
- diluting to 100 mL volumetric flask with RO water
what was the waste clean up for all the solutions in this experiment
all can go down the sink with lots of tap water
what was the final volume of solution A
100 mL
what was the density of Solution A
1.00 g/mL
what range do the visible wavelengths run from
400 nm to 800 nm
how would you get your absorbance reading to fall between the range of your curve if the absorbance reading is HIGHER than the range of the curve
dilute the solution
how would you get your absorbance reading to fall between the range of your curve if the absorbance reading is LOWER than the range of the curve
increase the concentration
