Investigation 2: Determination of the concentration of iron (II) ions in a commercial iron tablet (by
titration with standardised potassium manganate (VII)
Aim:
The objective of this experiment is to determine the quantity of iron (II) ions present in a commercial
iron tablet using the titration method. Titration is a chemical technique that entails the gradual
addition of a solution with a known concentration to a solution with an unknown concentration until
the reaction is complete. In this particular case, we will utilize a solution containing potassium
manganate (VII) with a known concentration, which will be gradually added to the solution
containing iron (II) ions until all of the iron ions are converted to iron (III) ions. The endpoint of the
titration is the point at which all of the iron (II) ions have undergone oxidation, and the colour of the
solution changes. To calculate the concentration of iron (II) ions in the tablet, we will need to know
the volume and concentration of the potassium manganate (VII) solution utilized in the titration. This
information will allow us to determine the quantity of iron (II) ions present in the commercial iron
tablet. By doing so, we can evaluate whether the iron tablet is meeting the required dosage and is of
excellent quality
Part 1: Standardization of Potassium Permanganate
Background:
In this laboratory experiment, we will be standardizing potassium permanganate, an oxidizing
substance, using a primary standard of sodium oxalate, a reducing agent. The goal of the experiment
is to accurately determine the concentration of the potassium permanganate solution. To begin the
experiment, we will need to prepare a 0.10 mol dm-3 sodium oxalate (COONa)2 solution. The
sodium oxalate will have been dried in a desiccator beforehand to remove any water. We will weigh
out the sodium oxalate quickly and accurately, minimizing its exposure to open air to avoid re-
adsorption of water. Then, we will quantitatively transfer the sodium oxalate to a 250 cm3
volumetric flask using deionized water and prepare the mixture accurately. Next, we will titrate the
sodium oxalate solution against the potassium permanganate solution. It is unusual for a
permanganate/oxalate redox titration to not require an additional indicator to determine the
endpoint. However, in this instance, potassium permanganate serves as its own indicator. When the
solution is in its oxidized state (MnO4-), it is purple in colour, but when reduced to its Mn2+ state, it
is colourless. The endpoint of the titration is reached when all of the sodium oxalate has reacted
with the potassium permanganate and the solution changes colour. At this point, we will record the
volume of the potassium permanganate solution used to reach the endpoint of the titration. We will
also need to know the concentration of the potassium permanganate solution, which we will
determine using the stoichiometric relationship between the two substances. Finally, we will use the
concentration of the standardized potassium permanganate solution to determine the concentration
of an unknown substance that can be oxidized by potassium permanganate. This will be done using a
similar titration procedure, where the unknown substance will be titrated against the standardized
potassium permanganate solution.
, Equipment
Part 1
A Weighing boat, five iron tablets, 100 cm3 conical flask with stopper, A label
Part 2
Beaker 250 cm3 ,Beaker 100 cm3 ,Glass stirring rod , deionised water ,Funnel to fit volumetric flask
neck, Weighing boat ,Spatula ,Burette ,Burette holder and clamp ,Retort stand, Volumetric flask 250
cm3 with stopper, Retort stand,25 cm3 pipette and filler ,25 cm3 measuring cylinder , Hotplate ,
Thermometer , Conical flask (either 100 or 250cm 3), White tile, Labels, Pasteur pipette
Healthy and safety
Lab coat to be worn with safety glasses
hazard warning and safety sign to be read before any work
Bags or coat must be kept under bench or completely out of the way
Spills or accident must be told to a teacher. Rinse skin instantly if any chemical touches
Broken glass must be cautiously place in the yellow glass bin provide
Chemicals
350 cm3 Potassium Permanganate solution 0.02 mol dm-3 -- the hazard associated with this
chemical are that is it highly toxic, it will cause respiratory problems when inhaled and cause
eye and skin irritation. By following the health and safety this risk can be minimized
200 cm3 Dilute sulphuric acid, approximately 1 mol dm-3 -- the hazard associated with this
chemical are it can cause chemical burns to your skin and eye, they are highly reactive and
can cause explosion, they are also an environmental hazard. By following the health and
safety this risk can be minimized
1 container of approximately ~3.5g dried sodium oxalate Balance -- the hazard associated
with this chemical are it can cause chemical burns to your skin and eye, they are highly
reactive and can cause explosion, they are also an environmental hazard. By following the
health and safety this risk can be minimized
