To Determine the Percentage by Mass of Calcium Carbonate in Eggshells

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Aim
The purpose of this experiment is to determine the percentage by mass of calcium carbonate in eggshells.

Introduction
To avoid the breakage of eggs before reaching market, the eggshells needs to be as strong as possible. The strength of eggshells is mainly determined by the percentage of calcium carbonate in it. In order to monitor the quality of eggshells, the following experiment has to be done to determine the percentage of calcium carbonate in eggshells. In this experiment, back titration is used. First, excess acid is reacted with the calcium carbonate in eggshells: 2HCl(aq) + CaCO3(s) → CaCl2(aq) + H2O(l)+ CO2(g)

Later, if we can find out the number of mole of unreacted acid, number of mole of calcium carbonate can then be found out. The number of mole of unreacted acid can be found by titration with the following reaction: HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)

Percentage by mass of calcium carbonate in eggshell can then be calculated by the following formula:

% by mass of CaCO3 =

Requirements

eggshell
burette, 50 cm3, and stand
pipette, 25 cm3
pipette filler
methyl orange indicator
1 M NaOH solution, standardized
1 M hydrochloric acid, standardized
ethanol
wash-bottle with de-ionized water
mortar and pestle
forceps
safety spectacles
2 beakers, 100 cm3
volumetric flask, 250 cm3
filter funnel, small
magnetic stirrer
pH meter
electronic balance

Procedures
1.The attached membrane of the eggshell was removed carefully by forceps and the remaining eggshell was ground into a fine powder with mortar and pestle. 2.2 g of powder was weighed accurately by the difference on an electronic balance and put into a beaker on a magnetic stirrer. 3.50cm3 of 1.003 M hydrochloric acid was added into the beaker by pipette and about 5 cm3 of ethanol was added into the beaker. The magnetic stirrer was turned on. Stirring was maintained until no more gas bubbles were seen. 4.The solution was transferred to a 250 cm3...
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