Determination of the amount (%) of iron in an iron tablet Flashcards
Apparatus needed
PESTLE AND MORTAR, safety glasses, clock glass, funnel, balance, beaker, stirrer, pipette, burette, 250cm³ volumetric flask, retort stand, conical flask, wash bottle with deionised water, white tile.
Material needed
Irons tablets, dilute sulphuric acid, standard solution of KMnO₄ (0.02M).
Why should this experiment get done ASAP?
As KMnO₄ concentration will continue to change as it is not stable in air, if we leave it for a period of time our results for the next experiment will not be accurate.
Is KMnO₄ a primary or a secondary standard?
Secondary
Why is KMnO₄ a secondary standard?
As it is not stable in air.
What is the first step in the method?
5 iron tablets were weighed accurately on a clock glass using a balance.
What was the mass of the 5 tablets when they were placed on the clock glass?
1.56g
What happens after the iron tablets were weighed?
The tablets were crushed using a pestle and mortar with some dilute sulphuric acid.
Why were the tablets crushed using a pestle and mortar with some dilute sulphuric acid?
To prevent aerial oxidation of the iron (II) in the tablets and to dissolve the tablets more quickly.
What happens after the tablets were crushed using a pestle and mortar with some dilute sulphuric acid?
This paste was then transferred to a 250cm³ volumetric flask using a funnel.
What happens after the paste was transferred to a 250cm³ volumetric flask using a funnel?
The pestle and mortar and funnel were washed several times with deionised water and the rinsings were added to the volumetric flask.
What happens after the pestle and mortar and funnel were washed several times with deionised water and the rinsings were added to the volumetric flask?
The solution was then made up to 250cm³ observing the usual precautions.
What happens after the solution was then made up to 250cm³ observing the usual precautions?
The pipette was washed with deionised water and some of the solution and then 25cm³ of this solution were transferred to a clean conical flask observing the usual safety precautions.
What happens after the pipette was washed with deionised water and some of the solution?
Roughly 20cm³ of dilute sulphuric acid was added to the solution in the conical flask.
Why was roughly 20cm³ of dilute sulphuric acid was added to the solution in the conical flask?
To ensure complete reduction of Mn(+7) to Mn(+2).
What happens after roughly 20cm³ of dilute sulphuric acid was added to the solution in the conical flask?
The burette was washed with deionised water and with some of the standard KMnO₄ solution.
What happens after the burette was washed with deionised water and with some of the standard KMnO₄ solution?
The burette was then clamped vertically and filled using a funnel to above the 0cm³ mark. The funnel was then removed. The tap was opened to fill the bit below the tap until the top of the meniscus was at the 0cm³ mark at eye level.
When were the solutions titrated until?
A permanent pink tinge was observed in the conical flask.
Results from burette
1st titre (rough) - 6.2cm³
2nd titre - 6.3cm³
3rd titre - 6.3cm³
Average titre
6.3cm³
Balanced ionic equation
MnO₄- + 5Fe₂+ + 8H+ → Mn₂+ + 5Fe₃+ + 4H₂O
Why are iron tablets sometimes medically prescribed? (L.C)
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Why must potassium manganate (VII) solutions be standardised? (L.C)
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Why was it necessary to standardise the potassium manganate (VII) solution immediately before use in the titration. (L.C)
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What reagent is used for ^^ purpose? (L.C)
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Describe how exactly 250cm³ of Fe₂+ solution was prepared from five iron tablets, each of mass 0.325g.(L.C)
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Why was some dilute sulphuric acid used in making up this solution?
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