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Chemistry Lab Exam > Colorimetric determination of Iron > Flashcards

Colorimetric determination of Iron Flashcards

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1
Q

what is one method for the determination of iron

A

based on the formation of the orange-red Iron(II)-orthophenanthroline complex

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2
Q

what is Iron(II)-orthophenanthroline often abbreviated to

A

“ferroin” with the molecule formula:

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3
Q

is orthophenanthroline an acid or base

A

base

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4
Q

what happens when orthophenanthroline is added to an acidic solution and WHY

A

it becomes pronated and giving up the phH+ ion because it is a BASE

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5
Q

what is the best pH for the formation of the Iron(II)-orthophenanthroline complex

A

3.5

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6
Q

why is a pH of 3.5 the best for the formation of the complex

A

because at this pH it is the best to PREVENT the formation of various iron salts (phosphates)

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7
Q

what is the importance of the hydroxylamine hydrochloride in this experiment

A

it is a reducing agent that prevents the iron (II) from being oxidized to iron (III) during the experiment

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8
Q

what is a benefit once the Iron(II)-orthophenanthroline complex forms

A

it holds it colour for a long period of time which allows for the determination of the concentration of the Iron(II)-orthophenanthroline complex

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9
Q

describe how colour is seen in the visible wavelength section of the electromagnetic spectrum

A

it “removes” them from the spectrum and the solution will appear to be a mixture of the colours NOT absorbed

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10
Q

what colours does the Iron(II)-orthophenanthroline complex absorb

A

green and blue light

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11
Q

what colour does the Iron(II)-orthophenanthroline complex appear

A

red-orange

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12
Q

what was the specific wavelength the Iron(II)-orthophenanthroline complex was measured at

A

508 nm (a shade of GREEN)

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13
Q

what is transmittance (T)

A

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)

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14
Q

is the relationship between transmittance and solution concentration direct or indirect

A

not direct

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15
Q

is the relationship between absorbance and solution concentration direct or indirect

A

direct

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16
Q

what is the equation for Beer’s Law

A

A=abc

17
Q

what do the different variables in Beer’s law indicate

A

A=abc

A is absorbance

a is absorptivity constant

b is cell width

c is the concentration

18
Q

what is the fundamental law governing the absorption of all types of electromagnetic radiation

A

A=abc

(Beer’s law)

19
Q

does Beer’s law only apply to solutions

A

NO - applies to solids and gases as well

20
Q

why is a blank used in spectrophotomerty

A

to correct for a loss in beam power at each interface due to reflection and scattering by larger molecules

21
Q

was it okay to use tap water, yes or no>

A

NO - tap water contains dissolved iron and other ions which messes with the results

22
Q

how much of the iron salt solution was put into a 50 mL beaker

A

about 40 mL

23
Q

what does iron salt refer to

A

Iron (II) ammonium sulfate hexahydrate

24
Q

how were the 5 different solutions and blank created in this experiment

A

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

25
Q

what can 1ppm be considered in water

A

1mg/L

26
Q

what were the axes of the calibration curve

A

x was concentration of Fe2+ in ppm

y was the absorbance values

27
Q

what are some health and safety reminders for HCl

A
  • causes severe burns
  • vapours irritate respiratory system and eyes
28
Q

how to prepare 26mL 6 M HCl from 12 M HCl

A

combine 13 mL of RO water with 13mL of the 12 M HCl

29
Q

how was solution A prepared

A
  • 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
30
Q

how was Solution B formed

A
  • 5 mL of solution A was pipet into a clean 100 mL volumetric flask
  • diluted to the mark with RO water
31
Q

how was the number of sodium citrate drops determined

A
  • pipet 10 mL of solution B into a smaller beaker and test pH
  • add sodium citrate drops until the pH was about 3.5
32
Q

how was solution c prepared

A
  • 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
33
Q

how was the blank for solution C prepared

A
  • 2.0 mL 10% hydroxylamine hydrochloride
  • 3mL Orthophenanthroline
  • required drops of sodium citrate
  • diluting to 100 mL volumetric flask with RO water
34
Q

what was the waste clean up for all the solutions in this experiment

A

all can go down the sink with lots of tap water

35
Q

what was the final volume of solution A

A

100 mL

36
Q

what was the density of Solution A

A

1.00 g/mL

37
Q

what range do the visible wavelengths run from

A

400 nm to 800 nm

38
Q

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

A

dilute the solution

39
Q

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

A

increase the concentration

Chemistry Lab Exam (4 decks)

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