如何準確找出雞蛋売內碳酸鈣(calcium carbonate)的百分比??

The problem comes from EXCESS HCl.

When the reaction complete, CaCl2, H2O and some HCl exist in the resulting solution because you use excess HCl. So it is not easy to separate two aqueous solutions from water.

A better method is as follows :

Firstly, immerse the egg shell in a known volume (V1) of standard 0.1 M HCl.

CaCO3 + 2HCl ---> CaCl2 + H2O + CO2 ( Reaction 1 )

Secondly, titrate excess HCl using standard NaOH ( aq ) with molarity M2.

HCl + NaOH ---> NaCl + H2O ( Reaction 2 )

Record the volume of NaOH ( V2 ) used.

The number of moles of NaOH = ( M2 )( V2 / 1000 ) = M2 V2 / 1000

So the number of moles of HCl in reaction 2 is M2 V2 / 1000.

Then find out the number of moles of HCl used in reaction 1: ( 0.1 V1 / 1000 ) - ( M2 V2 / 1000)

Let A denotes ( 0.1 V1 / 1000 ) - ( M2 V2 / 1000).

In reaction 1, the number of moles of CaCO3 = A / 2

The mass of CaCO3 present in the egg shell ( m ):

m / 100.1 = A / 2

Hence the percentage by mass of CaCO3 in the egg shell : (m / 10) X 100%

Hope it helps.