Determining the purity of Iron Wool.

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Subhir Bedi                                                                  Biochemistry Practical 2- Dr Wendy Gill

Determining the purity of Iron Wool

Introduction-

        The principal objective of the experiment was to determine the purity of a sample of iron wool using a form of titration, however, the experiment also highlights the importance of experimental errors and their consequences on the results collected as well as testing the accuracy of lab abilities.

        Iron (Fe) belongs to the transitions metals group of the periodic table and expresses all the fundamental characteristics that go along with this group, they are predominantly solid metallic in structure with equally high boiling and melting points.      

It’s the bonding in metals such as Iron which enable these types of characteristics, metallic ions such as Fe2+ are produced but the loss of electrons from atoms which along with free moving valence electrons create the “sea” of positively charged ions and negatively charged electrons.

Metallic Iron used today is extracted from a combination of Iron ore, Limestone and Coke under the conditions provided both by the structure and internal environment of a blast furnace. This process is summerised by the following equation:

Fe2O3(s) + 3CO(g)            2Fe(l) + 3CO2(g)

This Iron, known as “pig” Iron contains impurities which are removed by oxidation to create steel. Then through additional reactions using acids Hydrogen gas is liberated producing ferrous ion (Iron (III)).

The type of titration carried out during the experiment was for a redox reaction which is also known as an oxidation-reduction reaction.  This type of reaction involves the transfer of electrons from one unit to another. The oxidation number of all elements is always zero e.g. oxidation number of Fe in the metallic form is zero however the oxidation number of a substance as a monatomic ion equals the charge of that ion.1 

Oxidation and Reduction can be defined by the following:

Oxidation: the part in an oxidation-reduction reaction in which there is a loss of electrons by a species (or an increase in the oxidation number of an atom) 1

Reduction: the part in an oxidation-reduction reaction in which there is a gain of electrons by a species (or an decrease in the oxidation number of an atom) 1

The oxidation number in the experiment equation is:

MnO4-  +  8H+  +  5Fe2+                       Mn2+  +  4H2O  +  5Fe3+

Oxidation        +7                       5x(+2)                        +2                        5x(+3)

 Number

In the case of the equation above, Potassium Manganate VII has become an oxidizing agent and oxidized Fe2+ to Fe3+. There is also a change to the Potassium Manganate VII; it has been reduced to form a Manganese ion. The result is a near colourless aqueous solution which in the addition of the Potassium Manganate VII via the titration method turns the solution pink-ish marking the end point of the reaction.

Method:

1.40g of iron wool sample weighted out on a digital balance using a weighting boat after balance reading had been put to zero.

Using a measuring cylinder and collected 2.0M Sulphuric Acid (H2SO4) 75cm3 was measured out accurately and placed in a 250cm3 conical flask along with the weighted out sample of iron wool.

The flask was then placed on a hotplate inside a fume cupboard in order for dissolution to occur. Once heated it was removed from the hotplate and left to cool to room temperature. Although the solution was heated for sometime there may have been remnants of impurities which hadn’t dissolved and which could have affected the overall results.

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 In order to speed up this process cold water was poured around the bottom of the outside of the conical flask making absolutely sure no additional water got into or out of the flask.

 The solution was then poured into a 250cm3 flask using a funnel and made up to 250cm3 using deionised water making our stock solution. The funnel and any used/dirty apparatus were rinsed out using deionised waster as well. Using a pipette 25cm3 of the stock solution was extracted and place in a clean conical flask with the addition of 20cm3 of 1M sulphuric acid which had ...

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