How much iron is in an iron tablet?Group members: Choi Chuen Ching (5)

Fong Ka Yee (6) Leung Chi Lai (12)

Lui Lai Sin (16)

1. To investigate how much iron is in iron tablets.

2. To compare the percentage of iron in iron tablets from two different manufacturer.

3. To find out which one is worth buying.

Aim

Why iron is essential to our body?

Because iron is necessary for the formation of haemoglobin. The deficiency of iron may lead to a disease called anaemia, people who suffer this disease may need to take iron tablet under the guidance of doctor.

We can obtain iron from the following food sources:

Liver, eggs, beef, green leafy vegetables, etc.

Daily requirement of iron:

For male is 10mg and for female is 18mg.

Principles

A. Standardization of Potassium Permanganate SolutionPotassium permanganate slowly decomposes in solution, especially in sunlight and readily oxidizes organic matter. It has to be stored in brown bottle and has to be standardized before use.

The most common reagents which are used for the standardization of KMnO4 are oxalic acid, sodium oxalates, ammonium iron(II) sulphate or arenious oxide. KMnO4 is deep purple in color and is reduced to almost colorless solution (Mn2+ salts are light pink in color). It does not require a chemical indicator for the detection of end point.

In this experiment, ammonium iron(II) sulphate is used as a primary standard to standardize the KMnO4 solution. Solid ammonium iron (II) sulphate(AIS) is stable at room temperature and can be obtained in pure state. It can be used as a primary standard in redox titration. A neutral solution of AIS is unstable and iron will precipitate out as the hydroxide. Therefore it should be dissolved in an acidified solution, preferably oxygen free.

In this experiment, a standard ammonium iron(II) sulphate solution is used to standardize the potassium permanganate solution. The overall equation for the reaction is:MnO4

- + 5Fe2+ + 8H+ 　　　 Mn2 + 5Fe3+ + 4H2O

B. Determination of the mass of iron in one gram of the iron tablet

The iron in iron tablets comes from hydrated iron(II) sulphate (sometimes called hydrated ferrous sulphate). FeSO4 ． 7H2O. As its name suggests, iron(II) sulphate contains Fe2+ ions. These react with the MnO4

- ions in the potassium permanganate as shown in the equation below:5Fe2+ + MnO4 + 8H+ 　　　 5Fe3+ + Mn2+ + 4H2O

The colour of the potassium permanganate disappears as it reacts with the Fe2+ ions. This provides a way of deciding when the titration is complete because, when all the Fe2+ ions are gone, just one drop extra of potassium permanganate solution will make the titration mixture turn pale purple.

ProceduresA. Standardization of potassium manganate(VII) solution1) About 9.8G of ammonium iron(II) sulphate was accurately wei

ghed out. Then it was dissolved in 25ml of sulphuric acid. The mixture was diluted with distilled water and was made up to exactly 250.0ml of solution.

2) 25.0ml of this solution was pipetted into a conical flask. 25ml of 1M sulphuric acid was added to it.

3) It was titrated with potassium manganate(VII) solution until a permanent pink colour was obtained (would not disappear after 30 seconds).

4) The molaruty of the manganate(VII) solution was calculated.

B. Determination of the mass of iron in one gram of the iron tablet1)  Five iron tablets were weighed accurately and their masses were

recorded. .

2)  They were grinded up in a mortar and were pestled with about 5 cm3 of 1M sulphuric acid.

3)  The acid and tablets were transferred through a small filter funnel into a 250.0 cm3 volumetric flask. The mortar and pestle were rinsed with further quantities of acid, each portion were transferred carefully into the flask, until all trace of the iron tablets had gone.

4)  The funnel was rinsed with more acid, and then 1M sulphuric acid was added to the flask until the solution reaches the 250.0 cm 3 mark. The flask was stoppered and was inverted several times to mix the solution.

5)   25.0 cm3 of the solution was pipetted from the volumetric flask and was transferred to a conical flask.

6)   A burette was filled with the potassium manganate(VII) solution.

7)   The potassium manganate(VII) solution was titrated against the solution in the conical flask. The volume of potassium manganate(VII) solution used at the end point was recorded.

8)   The above steps were repeated but using different brands of iron tablets in step (1).

Standardization of potassium permanganate solution

Trial 1 2 3Initial/ml 0.10 0.10 0.20 0.00Final/ml 24.90 25.00 25.00 24.70

Vol. Used/ml 24.80 24.90 24.80 24.70

Result

Average volume used = 24.80ml

Enteric-coated 167mg iron tablets

Trial 1 2 3Initial/ml 0.00 3.00 5.70 8.40Final/ml 3.00 5.70 8.40 11.20

Vol. Used/ml 3.00 2.70 2.70 2.80

Average volume used = 2.73ml

Weight of 5 tablets = 1.067g

Enteric-coated 300mg iron tablets

Trial 1 2 3Initial/ml 0.95 6.45 17.50 22.85Final/ml 6.45 11.85 22.85 28.25

Vol. Used/ml 5.50 5.40 5.45 5.40

Average volume used = 5.42ml

Weight of 5 tablets = 1.580g

After calculation, we found that there is 142.76mg of iron present in the “167mg tablet” and 191.42mg of iron present in the “300mg tablet”.

Then we decided to remove the coating of the tablet and see whether the coating will affect the iron content.

How about the iron tablets without enteric-coating?

167mg iron tablets after removing the enteric-coat

Trial 1 2 3Initial/ml 0.00 2.55 4.90 7.25Final/ml 2.55 4.90 7.25 9.65

Vol. Used/ml 2.55 2.35 2.35 2.40

Average volume used = 2.37ml

Weight of 5 tablets = 0.959g

300mg iron tablets after removing the enteric-coat

Trial 1 2 3Initial/ml 36.20 40.70 45.00 39.10Final/ml 40.60 45.00 49.30 43.40

Vol. Used/ml 4.40 4.30 4.30 4.30

Average volume used = 4.30ml

Weight of 5 tablets = 1.312g

After calculation, we found that there is 138.48mg of iron present in the “167mg tablet” and 182.88mg of iron present in the “300mg tablet”.

DiscussionManufacturer of the iron tablets:

“167mg tablet” --- Christo Pharmaceutical LTD HK

“300mg tablet” --- Apotec Inc.

ManufacturerMass

Christo “167mg tablet”

Apotec “300mg tablet”

Tablets with enteric-coating

142.76mg 191.42mg

Tablets without enteric-coating

138.48mg 182.88mg

The table showing the mass of iron present in an iron tablet

It is found that the difference between the experimental value and the described value of the Christo is smaller than that of Apotec.

Manufacturer% of iron

Christo “167mg tablet”

Apotec “300mg tablet”

Tablets with enteric-coating

14.3% 19.1%

Tablets without enteric-coating

13.9% 18.3%

The table showing the % of iron present in an iron tablet

Source of error:

~The iron tablets are not completely dissolved in sulphuric acid.

~The percentage of iron in enteric-coating may not be the same as that of the inner part of the tablets.

~Potassium permanganate may decompose so that the volume of KMnO4 added may not accurate enough.

~The colour of the coating may affect the observation of end point during titration.

Observations:

We found that the “300mg tablet” is more difficult to dissolved in sulphuric acid.

Improvement:

~Potassium permanganate solution should be used immediately after pouring out of the brown bottle.

ConclusionWe found that the difference between the experimental value and the described value of “167mg tablet” was smaller than that of “300mg tablet”.

Therefore the manufacturer of “167mg tablet” (i.e.Christo Pharmaceutical LTD HK)is more reliable than that of “300mg tablet” (i.e. Apotec Inc.).

On the other hand, the price of both kinds of tablets were the same. So “300mg tablet” is more worth buying than “167mg tablet”.

The End