Determine the calcium carbonate content of a sample of an egg shell 08-09 Chemistry Report Determine the calcium carbonate content of a sample of an egg shell Members : Ho chi nam Tong wing kwan Chan siu sing Chan sing yeung Lee cheung fat

Introduction The pesticide DDT has caused significant damage to the environment and its wildlife. Birds are especially affected because the DDT weakens the shells of their eggs which would break before hatching. This caused certain bird species to become endangered (i.e. the American bald eagle). One method of monitoring the strength of the egg is by determining the percentage of calcium carbonate in eggshell

Principle During this experiment,the percentage of CaCO3 in an eggshell is determined by reacting the eggshell with hydrochloric acid. 2HCl(aq)+CaCO3(s)→Ca2+(aq)+CO2(g)+H2O(l)+2Cl-(aq)

Back titration This reaction cannot be used directly to titrate the CaCO3 because it is dissolved in water .Thus ,we must use back titration. Back titration is an analytical chemistry technique that allows the user to find the concentration of a reactant of unknown concentration by reacting it with an excess volume of another reactant of known concentration.

The resulting mixture is then titrated back, taking into account the molarity of the excess that was added. Through to find out the molarity of resulting mixture,we can calculate the abundant of an unknown sample

In this experiment,excess of standard hydrochloric acid is added to dissolve the eggshell. Ethyl alcohol is added to eggshell as a wetting agent to help the hydrochloric acid dissolve the CaCO3. Wetting agents are chemicals that increase the spreading and penetrating properties of a liquid by lowering its surface tension – that is, the tendency of its molecules to adhere to each other.

The remaining acid is titrated with NaOH solution. determine the amount of acid that did not react with the eggshell HCl(aq)+NaOH(aq)→H2O(l)+Na+(aq)+Cl-(aq) Through to find out the amount of acid ,we can calculate the abundant of CaCO3.

Experimental apparatus Wash bottle x1 Conical flask x4 Mortar and Pestle x1 Filter funnel x1 Electronic balance x1 50.00ml Burette x1 White tile x1 25.00ml pipette 250.00ml beaker x2 Oven x1 Bunsen burner x2 Tripod x2 250.00ml volumetric flask x2

Experimental Chemical Phenolphthalein 0.101188M NaOH 0.2175M HCl Enthanol Distilled water Paper towel Egg shell x2 (import form USA and Malaysia respectively)

Preparing fine egg shell powder: Procedure Preparing fine egg shell powder: Eggs were put into boiling water for 5 minutes. Eggshells of 2 eggs were washed with distilled water. Eggshells of 2 eggs were obtained by break the eggs shell.

The inside membrane was removed. The eggshell of 2 eggs was put into oven for 15 minutes. The eggshell powder of 2 eggs were ground by using mortar and pestle.

Preparation 0.20g of dried eggshells powder was weighed into each of 4 conical flask accurately. 25.00cm3 of 0.2175M HCl solution was pipetted into each flask. 5.00cm3 of ethanol was added to each flask. The flasks were swirled to wet all of the solid . Any excess HCl should be disposed in the sink by diluting with water.

The solutions in the flasks were heated until they began to boil and allow to cool .The walls of the flasks were rinsed with distilled water from the wash bottle. 3 drops of phenolphthalein was added to each flask.

7. A funnel was used to partly fill a clean burette with NaOH solution to rinse it. 8. The burette was filled with NaOH solution by using a funnel, and some solution were run out to remove all bubbles from the tip. 9. The initial volume was recorded.

10. Titrate the first sample to get a reference. 11. Titrate other three samples and record the results. 12. Calculate the percentage of calcium carbonate in each sample and the mean value. 13. Calculate the average deviation from the mean.

Results Table showing the titration result of Malaysia egg shell : Trial 1 2 3 Aveage Volume Final burette reading 26.1 26.6 25.2 27.2 Initial burette reading 1.5 0.5 2.8 3.4 Volume of NaOH used 24.6 22.4 23.8 24.1 Table showing the titration result of U.S.A egg shell : Titration Trial 1 2 3 Aveage Volume Final burette reading 28.6 29.2 30.2 47.8 Initial burette reading 0.1 0.4 17.7 Volume of NaOH used 29.1 29.8 30.1

Calculations the initial moles of HCl = 0.2175M x 25cm3/1000cm3 = 5.4375 x 10-3 mol HCl (aq) + NaOH (aq)→NaCL (aq) + H2O (l) 1 mole of HCl (aq) react with 1 mole of NaOH (aq) the moles of HCl react with NaOH = the moles of NaOH used =0.101188 x 24.1cm3/1000cm3 =2.4386308 x 10-3 mol

The moles of HCL react with CaCO3 = the Initial moles of HCl – the moles of HCl reacted with NaOH = 5.1875 x 10-3mol – 2.4386308 x 10-3mol =2.9988692 x 10-3mol

CaCO3 (s) + 2HCl (aq) →CaCl (aq) + H2O (l) + CO2 (g) 1 mole of CaCO3 react with 2 moles HCl The moles of CaCO3 = 2.9988692 x 10-3mol / 2 = 1.4994346 x 10-3 mol Percentage of CaCO3 in eggshell = 1.4994346 x 10-3mol x(40.1+12+16x3)g-mol/0.2g x 100 = 75.05%

the initial moles of HCl = 0.2175M x 25cm3/1000cm3 = 5.4375 x 10-3 mol HCl (aq) + NaOH (aq)→NaCL (aq) + H2O (l) 1 mole of HCl (aq) react with 1 mole of NaOH (aq) the moles of HCl react with NaOH = the moles of NaOH used =0.101188 x 29.8cm3/1000cm3 =3.015164 x 10-3 mol

The moles of HCL react with CaCO3 = the Initial moles of HCl – the moles of HCl reacted with NaOH = 5.4375 x 10-3 x 10-3mol –3.015164 x 10-3mol =2.4220976 x 10-3mol

CaCO3 (s) + 2HCl (aq) →CaCl (aq) + H2O (l) + CO2 (g) 1 mole of CaCO3 react with 2 moles HCl The moles of CaCO3 = 2.4220976 x 10-3mol / 2 = 1.2110488 x 10-3 mol Percentage of CaCO3 in eggshell =1.2110488 x 10-3 mol x(40.1+12+16x3)g-mol/0.2g x 100 =60.61%

Observations Bubbles appeared when dissolving egg shell powder by HCl(aq). Eggshell powder could not completely dissolve in HCl. The sodium hydroxide solution was colourless. When the sodium hydroxide solution was added to the mixture of eggshell and hydrochloride, the mixture turned pink.

Remarks Ethanol must be added before the boiling of mixture of eggshell and hydrochloride. The ethanol should be stored in a closed vessel and was pipette only when it was used. When the mixture heated to 80oC,the titration was started immediately. Shark flask continuously during the titration. Make sure that the eggshell powder was dry. The conical flask should be heated by air bath because the mixture contain ethanol which is flammable.

Source of error Variation in visual judgement at the end point. Eggshell powder could not dissolve completely in HCl. The inside membrane was not completely removed. The mixture was not heated enough. Although after through rinsing,not all the eggshell powder is transferred to the volumetric flask.

Precautions The hydrochloride acid and Sodium hydroxide solution are corrosiveness. During the heating, the safety goggles must be weared. Label the containers of each solution because they are colorless solution. We should wash our hands after the experiment.

It reflect that the pollution of DDT is more serious in U.S.A Conclusion Though the experiment,the egg of Malaysia was found that the percentage of CaCO3 was 75.05%. The egg of U.S.A. was found that the percentage of CaCO3 was 60.61%. The egg of Malaysia contain more CaCO3 than the egg of U.S.A. It reflect that the pollution of DDT is more serious in U.S.A