Chemistry project • To determine the percentage of calcium carbonate in eggshell • Lin Yin Shing (23) • Hung Ching Yin(4) • Wai Sze Wah (8) • Poon Yee Man (7) • Yuen Chun Fai (30)
Content • Introduction • Principle of this experiment • Apparatus and equipments • Experiment procedures • Chemical used • Sample used • Source of errors • Assumption made • Experimental results • Calculations • Conclusion • Sources of references
Introduction • 1960's - 1970's USA used a pesticide, DDT extensively • Run-off from DDT entered our waterways and eventually into many of our wild birdlife. • DDT affected the population by weakening the eggshells which would break before hatching. • An example of this devastation was the American Bald Eagle whose population was as low as 400 mating pairs in the lower 48 states. • DDT has been banned in the USA and the Bald Eagle is no longer on the endangered species list. One method of monitoring the strength of the egg is by determining the percentage of calcium carbonate in the eggshell. • This can be accomplished through an acid/base titration method.
Principle of the experiment • During this lab, the percentage of CaCO3 in an eggshell is determined by reacting the eggshell with hydrochloric acid. The equation for this reaction is: • 2HCl (aq) + CaCO3(s) →Ca2+ (aq) + CO2(g) + H2O(l) + 2Cl- (aq) • This reaction cannot be used directly titrate with the CaCO3. Instead, an excess of hydrochloric acid is added to dissolve the eggshell, and the remaining acid is titrated with NaOH solution to determine the amount of acid that did not react with the eggshell. The equation used to determine the amount of leftover acid is: • HCl(aq) + NaOH(aq) → H2O(l) + Na+(aq) + Cl- (aq)
In order to help the hydrochloric acid dissolve the CaCO3, ethyl alcohol is added to the eggshell as a wetting agent. 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. • Although it is now banned in the United States, 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 the eggshell. • The percentage of calcium carbonate indicate that the strength of the eggshell . And the strength of the eggshell show how serious the pesticide damaged to the eggshell.
Apparatus and equipments • 250.00 cm3 beaker X4 • glass rod X1 • Filter funnel X1 • Wash bottle X1 • Electronic balance X1 • Weighing bottle X1 • 250.00cm3 volumetric flask X2 • 25.00 cm3 pipette X2
Conical flasks X2 • Measuring cylinder X1 • Bunsen burner X2 • Heatproof mat X1 • Burette X2 • Wire gaze X2 • Tripod X2 • White tile X2 • Mortar and pestle X2 • Oven X1
Chemical used • 0.1M NaOH • 0.2M HCl • Phenolphthalein • Ethanol
Sample used • 2 different eggs (1 white & 1 brown) USA Malaysia
Procedures • The eggs was boiled and cooled down. • The protein membrane was removed on the inside of the boiled eggshell. • The eggshell was washed with distilled water
The eggshell was then grounded into fine powder by mortar and pestle. (white egg) (brown egg)
0.2g of eggshell powder is weighted accurately by using an electronic balance and it was transferred to a conical flask.
25.00 cm3 of HCl was pipetted to dissolve the eggshell powder and 5 cm3 of ethanol was also added in order to help the HCl dissolve the CaCO3 • Distilled water was added to the flask until it reached about 50cm3. The flask was swirled gently.
The mixture was boiled for about 15 minutes (boiling away CO2) and then cooled down.
Boil !! Cool down!! 15 minutes!!!
Experimental set-up NaOH Burette stand Burette 25.00cm3 of HCl + 0.2g if egg shell powder + 5.00cm3 of ethanol + 3 drops of phenolphthalein + about 20.00cm3 of distilled water stopcock Jet Conical flask White tile
The solution was then titrated with standardized NaOH. • Repeat another sample
Experimental results The colour change of the solution: White egg: Colourless pink Brown egg: Colourless pink
The titration result of brown egg: Average volume of NaOH used: (20.00+18.30+13.10)/3=17.13cm3
The titration result of white egg: Average volume of NaOH used: (19.60+19.80+19.70)/3=19.7cm3
Calculations 2HCl (aq) + CaCO3(s) →Ca2+ (aq) + CO2(g) + H2O(l) + 2Cl- (aq) HCl(aq) + NaOH(aq) → H2O(l) + Na+(aq) + Cl- (aq) For brown egg: Number of moles of NaOH used to react with HCl: (17.13cm3 /1000) X0.1M = 1.713 X 10-3 mol Since number of moles of NaOH = number of moles of HCl = 1.713 X 10-3 mol The initial no of moles of HCl: volume X molarity = 25/1000 X0.2M = 5X10-3 mol Number of moles of HCl used to react with CaCO3 : (5X10-3 - 1.713 X 10-3) mol=3.287 X10-3 mol
According to the equation, one mole of HCI required to react with 2 moles of CaCO3, Number of moles of CaCO3 reacted: 3.287X10- 3 /2 = 1.6435X10-3 mol The weight of CaCO3: 1.6435X10-3g X100.1 =0.1645g The % of CaCO3 in eggshell (brown) : (0.1645/0.2) X100% =82.25%
For white egg: Number of moles of NaOH used to react with HCl: (19.7/1000)X0.1 = 1.97X10-3mol Since number of moles of NaOH = number of moles of HCl = 1.97X10-3mol The initial moles of HCl: volume X molarity = 25/1000 X0.2M = 5X10-3 mol Number of moles of HCl used to react with CaCO3 : ( 5X10-3 - 1.97X10-3) mol =3.03 X10-3 mol
Number of moles of CaCO3 reacted: 3.03 X10-3/2 = 1.515X10-3 mol The weight of CaCO3: 1.515X10-3g X100.1 =0.15165g The % of CaCO3 in eggshell (white) : (0.15165/0.2) X100% = 78.83%
Summary of Calculations For Brown egg:
Sources of errors • The eggshell powder did not dissolve completely • Variation in visual judgement at the end point • Instrumental errors of the electronic balance • The eggshell was not fully dried • Some droplets of solution may still adhere on the beaker and the glass rod which lead to the reduction in number of moles of excess HCl we should wash our hands after the experiment • There was vaporization during boiling.
Remarks • During titration, control the stopcock of the burette with your left hand. Swirl the conical flask with your right hand • Use a conical flask to dissolved the eggshell since colourless gas bubbles will be evolved. It is to prevent the solution from jumping out .(CO2 is formed) • When dissolving the eggshell in a conical flask, use a stirrer to stir the solution well in order to make sure that the eggshell is totally dissolved • After pouring the solution mixture of eggshell and HCl into a volumetric flask, remember to rinse the stirrer and the conical flask with distilled water and pour the washing to the volumetric flask • After filling up the burette with NaOH, we should remember to remove the filter funnel on the top of the burette • Bubble in the burette should be removed before the initial reading of the burette is read • we should swirl the conical flask after each addition. Distilled water should be added to rinse the NaOH down the flask • Put a white tile under the conical flask for clearer observation
Safety precautions • Dilute NaOH is corrosive • Do not touch chemicals with bare hands • Safety goggles should be put on during the experiment • We should wash our hands after the experiment
Conclusion • By comparing the percentage of two eggs, brown egg (Malaysia) has a higher percentage than white egg (USA) indicate brown egg has a higher strength than white egg. It also show that eggs from USA have a more serious problem of using DDT.
Group members • Hung Ching Yin (4) Took photos, Typing, Search for information, Calculations, Grouping information • Wai Sze Wah (8) Typing, Search for information, Calculations • Poon Yee Man (7) Record the results, typing, search for information, Design PowerPoint • Lin Yin Shing (23) Typing, search for information • Yuen Chun Fai (30) Typing, search for information, Caclculations
Sources of references • http://www.chem.csustan.edu/chem1102/Egg.htm • www.wikipedia.com