Chemistry Project 06 - 07 Lau Ching Fai(8) Tze Chi Ho(21) Kwan Siu Hong(5) Lee Chun Tak(10)

Title: To determine the percentage of calcium carbonate in eggshell

Principle The major component of eggshells is calcium carbonate (CaCO3). Calcium carbonate (limestone) is very insoluble in pure water but will readily dissolve in acid according to the equation :  2HCl (aq) + CaCO3(s) ----> Ca2+(aq) + CO2(g) + H2O(l) + 2Cl- (aq) By adding an excess of acid to dissolve all of the CaCO3 and then titrating the remaining H3O+ with NaOH solution to determine the amount of acid which has not reacted with the calcium carbonate. The difference between amount of the acid (HCl) initially added and the amount left over after the reaction is equal to the amount used by the CaCO3. The reaction used to determine the leftover acid is according the equation:    HCl (aq) + NaOH (aq) ----> H2O(l) + Na+(aq) + Cl-(aq)

Chemicals: Sample A (Brown Eggs) x 1g Sample B (Leghorn Eggs) x 1g Hydrochloric acid(1M) x 50ml Distilled water x 100ml Sodium hydroxide (0.2M) X 200ml Ethanol x 30ml Phenolphthalein (a few)

Experimental procedures: Eggs were boiled Removed the eggshell that the protein membrane was left behind The eggshells was ground into fine powder Placed the ground powder in a drying oven for about 10 minutes Weighed accurately about 0.1 gram of each sample into a conical flask

Added 5ml ethanol into the flask (This acts as a wetting agent and helps the HCl dissolve the CaCO3) Added 10ml hydrochloric acid(1M) into the flask Heated the solutions in the flasks until they begin to boil and allow to cool

Add 3-4 drops of phenolphthalein to each flask Filled the burette with the NaOH(0.2M) solution Recorded the initial volume and titrate the sample with NaOH to persistent pink color Read and recorded the final volume Repeated the titration with other samples

Mass of eggshell dissolved Experimental results: Sample A : Brown Eggs Sample B : Leghorn Eggs Table to show the result of weighing Trial 1 Trial 2 Trial 3(only sample B) Sample A B Bottle + eggshell 8.02g 8.49g 8.10g 8.55g 8.03g Bottle + residue 7.92g 8.36g 7.97g 8.43g 7.90g Mass of eggshell dissolved 0.1g 0.13g 0.12g

Initial burette reading Table to show the result of titration Sample A Sample B Trial 1 Trial 2 Trial 3 Final burette reading 43.2 cm3 44.3 cm3 41.9 cm3 43 cm3 39.9 cm3 Initial burette reading 1.2 cm3 4.8 cm3 1.9 cm3 2.1 cm3 1.0 cm3 Volume of NaOH used 42 cm3 39.5 cm3 40 cm3 40.9 cm3 38.9 cm3 Average : 40.8 cm3 Average : 39.9 cm3

Calculations: Calculate the number of moles of HCl added to each shell sample Calculate the moles of HCl left in each sample after the reaction with CaCO3 For each sample determine the number of moles of HCl that has reacted with CaCO3 by taking the difference between the moles of HCl added and the moles of HCl remaining after the reaction is complete The moles of CaCO3 in each sample Calculate the percent CaCO3 in each sample

For Sample A (Brown Eggs) Trial 1 Trial 2 Mass of eggshell 0.10 g 0.13 g Volume of HCl 10ml Volume of NaOH 42 cm3 39.5 cm3 Moles of HCl (10/1000)(1) = 0.01 mol Moles of NaOH to neutralize the excess moles of HCl (42/1000)(0.2) =0.0084 mol (39.5/1000)(0.2) =0.0079 mol mol of HCL reacted = mol of HCL - mol of NaOH 0.01 – 0.0084 =0.0016 mol 0.01 – 0.0079 =0.0021 mol mol of CaCO3(1/2mol of HCL reacted) 0.0008 mol 0.00105 mol Molar mass of CaCO3 100.1 g mol-1 percentage of CaCO3 Trial 1 (0.0008)(100.1)(100%)/0.1=80.08% Trial 2 (0.00105*100.1*100)/0.13=80.85% Average : (80.08+80.85)/2=80.465%

Sample B (Leghorn Eggs) Trial 1 Trial 2 Trial 3 Mass of eggshell 0.13 g 0.12 g Volume of HCl 10ml Volume of NaOH 40 cm3 40.9 cm3 38.9 cm3 Moles of HCl (10/1000)(1) = 0.01 mol Moles of NaOH to neutralize the excess moles of HCl (40/1000)(0.2) =0.008 mol (40.9/1000)(0.2) =0.00818 mol (38.9/1000)(0.2) = 0.00778 mol mol of HCL reacted = mol of HCL - mol of NaOH 0.01 – 0.008 =0.002 mol 0.01 – 0.00818 =0.00182 mol 0.01 – 0.00778 = 0.00222 mol mol of CaCO3(1/2mol of HCL reacted) 0.0001 mol 0.00091 mol 0.00111 mol Molar mass of CaCO3 100.1 g mol-1 percentage of CaCO3 Trial 1 (0.001*100.1*100%)/0.13=77% Trial 2 (0.00091*100.1*100)/0.12=75.9% Trial 3 (0.00111*100.1*100)/0.13=85.47% Average: (77+75.9+85.47)/3=79.157%

Remarks: Safety goggles should be put on during heating Be careful when using Bunsen burner Take great care of 1M HCl because it is corrosive Dilute the acid by pouring it into sink with slowly running water Sources of errors: The eggshell powder did not dissolve completely. Some ethanol may evaporated. The eggshells may contained impurities. Variation in visual judgment at the end point.

Conclusion: As the percentage of CaCO3 in Brown Eggs and Leghorn Eggs are 80.465% and 79.157% respectively, these show that the main component of eggshells is CaCO3. This result is less than our expectation because of the presence of DDT. How does DDT affect the thinness of eggshell? Let’s get an answer……..

Further study - The side effects of DDT DDT is a colourless crystalline substance which is practically insoluble in water but highly soluble in fats and most organic solvents. It kills insects by opening sodium ion channels in neurons, causing the neuron to fire spontaneously Side effects: DDT cause cancer Killing higher level organisms like the birds. Harm bird reproduction by weakening and thinning eggshells since eggshells mainly contain CaCO3 Therefore DDT should be banned The molecular structure of DDT

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