12.1 Flashcards
12.1 Investigating iron tablets. • To research and plan a short investigation
You will plan how to determine the iron content in iron tablets. You will use research skills to find the necessary information, and then carry out your planned procedure.
‘Iron tablets’ are prescribed by doctors to treat anaemia (iron deficiency). The outer coating of an iron tablet breaks down in the acidic environment of the stomach to release the water-soluble iron(II) compounds inside the tablet.
The aim of this task is to plan an experiment to find the exact mass of iron contained in an iron tablet. One method of finding the concentration of Fe2+ ions in a solution is titration using potassium manganate(VII) solution. You will need to research this technique, and plan how to use it in this context.
Aims
Equipment
Chemicals
You will be provided with:
• a maximum of 5 iron tablets
• a standard solution of potassium manganate(VII), KMnO4(aq), 0.0200 mol dm3
• aqueous sulfuric acid, H2SO4(aq), 1.00 mol dm3.
Your research will help you decide which pieces of laboratory apparatus you will need.
Learners will be selecting appropriate apparatus for the experiment. It is likely that they will require
• safety spectacles
• conical flasks (100 cm3 or 250 cm3), with bung
• measuring cylinder (100 cm3)
• volumetric flasks (100 cm3 or 250 cm3)
• filter funnel and paper
• burette, stand and clamp
• pipettes (10 cm3 or 25 cm3) and filler
• white tile
• wash bottle containing distilled or de-ionised water
- What iron tablets contain.
- The role of iron in the body, and why some people need to take iron tablets?
- The approximate mass of iron present in a standard iron tablet?
- The recommended daily intake of iron?
- Details about a titration method using potassium manganate(VII) solution that can be used to find the concentration of Fe2+ ions in a solution.
- The chemistry on which this titration is based.
What iron tablets contain, and the approximate mass of iron present in iron tabletsThis will depend on the tablets provided. The active ingredient in most iron tablets is iron(II) sulfate, FeSO4 (200 mg), equivalent to 65 mg iron. Some iron tablets contain iron(II) fumarate, FeC4H2O4, as the active ingredient.
Tablets will contain additional inactive ingredients that e.g. make up the coating, act as a binder, flavouring agent etc.
The role of iron in the body, and why some people need to take iron tablets
Iron is a mineral that the body needs to produce red blood cells. When the body does not get enough iron, it cannot produce the number of normal red blood cells needed to keep you in good health. This condition is called iron-deficiency anaemia. Iron supplements work by replacing body iron.
Recommended daily intake
- 7 mg a day for men
- 8 mg a day for women
Titration method
Most methods involve the use of a pestle and mortar to grind up the tablets before making up a solution in dilute sulfuric acid. Learners could choose to make up a single solution of all 5 tablets in a 250 cm3 volumetric flask, and then titrate 25 cm3 aliquots. Alternatively, they could make up solutions of one tablet at a time and titrate each one separately. Learners will need to indicate what concentration of potassium manganate(VII) they will use, and the approximate quantity they will require.
The chemistry on which the titration is based
The reaction that takes place during the titration is:
5Fe2+ + MnO4 + 8H+ 5Fe3+ + Mn2+ + 4H2O
Iron tablets
Commercial iron tablets. Usually labelled ‘200 mg’ and containing 65 mg iron in the form of soluble Fe(II) ions.
Each learners or group should be given 5 tablets.
The packaging should be made available to learners so that they can find information regarding the identity and mass of the active ingredient. No hazard classification
Commercial iron tablets.
Usually labelled ‘200 mg’ and containing 65 mg iron in the form of soluble Fe(II) ions.
Each learners or group should be given 5 tablets.
The packaging should be made available to learners so that they can find information regarding the identity and mass of the active ingredient. No hazard classification
KMnO4(aq)
Currently no hazard classification at this concentration
H2SO4(aq)
Causes skin irritation
Causes serious eye irritation
note
http: //papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_nos_ps_3.pdf
http: //en.wikibooks.org/wiki/Applied_Science_BTEC_Nationals/Chemical_Laboratory_Techniques/Iron_tablet
procedure
Method 1
- Crush 5 iron tablets with a pestle and mortar.
- Make up a solution of the tablets in 1.00 mol dm3 H2SO4(aq) in a 250 cm3 volumetric flask.
- Titrate 25 cm3 aliquots of this solution with 0.0100 mol dm–3 KMnO4(aq) until concordant results are obtained.
- The mean titre should be about 11.5 cm3.
- This method also works well by dissolving 2 tablets in 100 cm3 in 1.00 mol dm3 H2SO4(aq) and then titrating 10 cm3 aliquots with 0.00500 mol dm3 KMnO4(aq). In this case the mean titre should be about 9.3 cm3.
Method 2
Outlines of example methods and expected results are given below.
- Crush 1 iron tablet with a pestle and mortar.
- Dissolve in 1.00 mol dm3 H2SO4(aq) in a conical flask. (About 50 cm3 solution would be appropriate, but the exact volume does not matter.)
- Titrate with 0.0100 mol dm–3 KMnO4(aq).
- Repeat until concordant results are obtained.
- The mean titre should be about 23 cm3.
plan to investigate the speed of release of Fe2+ from an iron tablet. This activity is difficult to carry out in a classroom setting, as some iron tablets can take more than 24 hours to release all of the soluble iron(II) compounds they contain. However, learners should be able to suggest a method for conducting this investigation.
Possible methods include:
- adding an iron tablet to a volume of sulfuric acid (the pH of an empty stomach is usually close to 2, http://scienceline.ucsb.edu/getkey.php?key=275); removing portions of the solution at set intervals for direct titration with potassium manganate(VII) solution
- setting up multiple experiments consisting of iron tablets in sulfuric acid, filtering each mixture after a different amount of time, making each filtrate up to a fixed volume and titrating portions of these solutions.
The following research papers describe ways in which the rate of dissolving can be measured.
- http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3585894/
- www.ncbi.nlm.nih.gov/pubmed/24482777
