Aim: To estimate volumetrically the amount of Calcium carbonate present in the eggshell and analysing the sources of errors to evaluate the results.
Hypothesis: Back Titration is used instead of conventional acid-base titration when one of the reactants is not very soluble in water.
Independent variable: Potassium hydrogen phthalate, Volume of HCl, Weight of Eggshell
Dependent variable: Concentration & volume consumed of NaOH. Concentration of Calcium Carbonate in the eggshell
Controlled variables: Phenolphthalein solution, Ethanol
1 Boiled Egg
The experiment is divided in to three parts.
Part A: (Standardisation of 1 M NaOH)
We used the watch glass to take 2g of Potassium hydrogen phthalate and then recorded its exact mass up to 2 decimal figures. Then we transferred the salt into a 250ml conical flask and added 50ml of distilled water; swirled the flask to dissolve the salt by taking care that nothing remains in excess.
We added 2-drops of phenolphthalein indicator to the solution in the conical flask and then we started doing titration by keeping NaOH in the burette. Then we kept of doing that until we reached the end point of it which was the change of colour from colourless to (pink), we recorded the Volume of NaOH consumed and calculated the molarity of the NaOH,
Part B: (Standardisation of 2 M HCl)
We took 10ml of HCl in the conical flask and added 2-drops of phenolphthalein indicator and then we titrated it by taking standardized solution of NaOH in the burette.
The end point of the titration was again the same the colour change from colourless to (pink), we recorded the volume of NaOH consumed and then did the calculation to figure out the exact molarity of the HCl.
Part C: (Amount of Calcium Carbonate present in the Egg-Shell)
The experiment was done in three steps:-
By removing the egg shell from the boiled egg, we collected the shell in a watch glass; weighed it and recorded the mass, then we transferred the shells pieces into 250ml conical flask
We added 20ml of ethanol and 60ml of standardised HCl taking care of putting ethanol before HCl, and then we did the time consuming work and started swirling the conical flask till we saw no more reaction. We took care of not letting any piece of shell be unreacted.
And then we added 2-drops of phenolphthalein indicator we titrated the contents of the flask with the standardised NaOH solution, Again the end point of the titration was change in colour from colourless to (pink), we recorded the volume of NaOH consumed.
The values obtained by me are completely based on the data recorded, but yes there were systematic and random error while calculating the values,
Systematic errors like parallax, random errors like taking readings and adding excess NaOH.
On overall conclusion, the lab was set perfectly well with just a little bit of error, and nothing else, just there was a little bit mistake made by me when I was calculating the weight of watch glass with eggshell I was not able to transfer all the pieces of eggshell in the conical flask which might have reflected in my errors. There was a chance of getting an error in reading by letting the dipping NaOH to touch the walls of conical flask but that was take care by us and ensured that not even a single drop touches the wall.
I found some errors in the procedure of calculating the weight of eggshell and salt, we were supposed to check weight of salt and eggshell on the watch glass which was a perfect measurement but the mass of both when they were transferred to the conical flask some bit of it still remain on the watch glass or fell over. The experiment was quite perfect with least amount of uncertainties as quite accurate digital products were used to measure the weight and the only error was the error caused by parallax and one mentioned above. The volume is calculated in ml which is converted into dm3 which decreases the uncertainty of it. The overall quality of data is good but, the readings are précised but not exactly accurate that is because of huge alteration between the volumes of NaOH, yes there is another error of human reflection to the change in colour of liquid from colourless to pink which is an random error,
The equipment used is Analytical Balance, Watch Glass, Beaker 100(ml), pipette bulb, Conical Flask- 250(ml), Burette, Funnel, and Stand. The reaction between the eggshell and the HCl, Ethanol took a lot of time so we were supposed to calculate the readings for the Part C the eggshell one at the first place. That saved our time and gave us time to complete the full experiment within the given time. The readings of data were perfect and I don’t think that I need much changes.
The only thing that can be changed is using a steriliser which will reduce the time of reaction, and secondly I feel that using the same flask for three readings and cleaning it with distilled water was not accurate.
There no such important issues to be dealt in the experiment as the apparatus used were accurate but we had some random errors due to human’s indulgence in calculating the readings, that was solved by using uncertainty values.
The reading taken is once so we cannot be completely sure about the reading if we could have done it twice then we might have got the average readings which may have been a better judgement.