FInding the percentage purity of CACO3 in egg shell

Authors Avatar by crysisfreak69 (student)

Aim

 Egg shell is hard and cracks easily when beaten because of the constituent of CaCO3.Our main aim will be to determine the purity or the percentage composition of CaCO3 in the egg shell by using the technique of back titration. The egg shell is just a representation of any substance containing CaCO3 in their constitution; this method could be used to find the percentage purity of marble, limestone, sea shell etc.

Identification of Variables

Independent variable

  • Purity of CaCO3 in the egg shell

Dependent Variable

  •   Volume of Hcl

Controlled Variable

  • Concentration of Hcl

The concentration of Hcl that is going to be used must be calculated for the experiment for show results. I took 4.931 g of egg shell which is 0.04931 moles. We will be following the procedure of back titration in this experiment since CaCO3is insoluble in water/reacts slowly with acid. Thus the first procedure of back titration is to react the substance with excess of acid , which means that we have to take a slightly high concentration of a preferred acid , in this experiment we have taken 2M of Hcl acid. If we don’t take excess of acid then the substance will not react completely with the acid and hence this will then lead to major inaccuracies in the experiment and the result of the experiment will be wrong  , having large discrepancy.

  • Concentration of NaOH

The NaOH concentration that will be used in the experiment will be prepared before performing the experiment whose concentration is known. In the second stage of titration, contrary to the first stage we do not use excess of NaOH. The amount of NaOH that has to be used is calculated before the experiment is done in order to know the exact amount of alkali that will be required to neutralize the base. The concentration is calculated by finding a good orientation of the number of moles that will react with the volume that will be needed. If the concentration of NaOH used due to inaccurate calculation is little then while titrating the burette will show great volume of NaOH that will be required to neutralize the acid hence an error, and if the concentration used is high then the burette will show a lower value of the volume of the alkali that will be required to neutralize the base.

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  • Room temperature at which the experiment is performed

There can be a difference in the concentration of the solution if the solution prepared and the experiment performed is at different temperatures .Hence an ideal way to control the variable would be to prepare the solution and perform the experiment at the same temperature.

  • Mass of the egg shells

The mass of the egg shells that is taken is controlled by the person performing the experiment. This is the major variable  , as according ti this variable all other variable are dependent of this.If we take a higher mass of egg ...

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