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Determine the mass of calcium carbonate in chicken eggshells Essay

ApparatusUncertainty
25.00 cm3 pipette
± 0.03 cm3
50.00 cm3 burette
± 0.05 cm3
250.0 cm3 volumetric flask
± 0.3 cm3
50.0 cm3 measuring cylinder
± 0.5 cm3
Electronic balance± 0.01 g
Uncertainty of apparatus

Measurement
Mass of eggshell = 3.15 ± 0.01 g
Volume of HCl added = 50.00 ± 0.5 〖cm〗^3
Volume of solution = 250.0 ± 0.3 〖cm〗^3
Volume of NaOH pipetted = 25.00 ± 0.03 〖cm〗^3
Titration number Rough12
Initial burette reading of NaOH/
± 0.05 cm3
0.000.000.00
Final burette reading of NaOH /
± 0.05 cm3
11.8011.7011.20
Volume of NaOH titrated / ± 0.10 cm3
11.8011.7011.20

Titration table: data collected from burette of amount of HCl used for the colour of the solution with methyl orange to change

Qualitative observation

When added with eggshell solution, methyl orange turns from orange to pink. When titrated with NaOH, methyl orange turns from pink to orange. Bubbles or foams are formed when HCl is added to the eggshells

Data processing (3 sig. fig)Error propagation (2 d.p)
Average volume of NaOH
(11.70+11.20 )/2=11.45 〖cm〗^3 ∆ of burette = (0.10+0.10)/2 = 0.10 〖cm〗^3

Number of mols of NaOH used for titration
0.50 × 11.45/1000=0.00575 mols % ∆ of burette = 0.10/11.45 × 100 % = 0.87 %
Using mole ratio,
HCl : NaOH
1 : 1
Number of moles of HCl in 25.00 〖cm〗^3 of solution
= 0.00575 mol% ∆ of moles = 0.87 %
Number of moles of excess HCl in 250.0 〖cm〗^3 volumetric flask 0.00575 × 250.0/25.00=0.0575 mols % ∆ of pipette
0.03/(25.00 ) × 100 % = 0.12 %
% ∆ of volumetric flask
0.3/250.0 × 100 %= 0.12 %
% ∆ of moles of HCl
0.12% + 0.12% + 0.87%
= 1.11%
Initial mole of HCl added to eggshell
2.00 × 50/1000 = 0.100 mols % ∆ of moles of HCl
0.50/50 × 100%=1.00%
Number of moles of HCl reacted with CaCO_3
0.100 – 0.0575 = 0.0425 mols∆ mols of HCl added
1.00/100 × 0.100=0.001 mols
∆ mols of excess HCl
1.11/100 × 0.0575 = 0.000638 mols
∆ mols of reacted HCl
0.001 + 0.000638 = 0.00164 mols
% ∆ of mols of HCl reacted
0.00164/0.0425 × 100% = 3.86%
Using mole ratio,
CaCO_3 : HCl
1 : 2
Number of moles of CaCO_3 reacted
0.0425 × 1/2 = 0.0213 mols% ∆ mols of CaCO_3 = 3.86 %
Mass of CaCO_3 in eggshell
0.0213 × 100.09 = 2.13 g % ∆ of mass of CaCO_3 = 3.86%
∆ mass of CaCO_3
3.86/100 × 2.13 = 0.08 g
% of CaCO_3 in eggshell
2.13/3.15 × 100% = 67.6%% ∆ of mass of eggshell
0.01/3.15 × 100% = 0.317%
Total % uncertainty
0.317% + 3.86% = 4.20%

Total % uncertainty = 4 %

Mass of CaCO_3 in eggshell = 2.13 ± 0.08 g

% of mass of CaCO_3 in chicken eggshell = 67.6% (3sf)

Conclusion
In my experiment, the percentage by mass of calcium carbonate in chicken eggshell was 2.13 ± 0.08 g. the total % uncertainty of my experiment is about 4%. From the information given, a good quality dry eggshell contains 94% of calcium carbonate. By calculation, % error = |(67.6-94.0)/94.0 | × 100% = 28%, the % error is 28%. Providing my % uncertainty is lesser than my % error, my experiment can be concluded that it has significant systematic errors. Also, by looking at the percentage by mass of CaCO_3 of 67.6%, comparing with a good quality eggshell, which contains 94% of CaCO_3, it can be concluded that my eggshell quality is not good.

Evaluation
One source of error is the fizziness of the reaction due to gas evolved. This is a type of random error. This will cause mass loss due to acid spray would be included as mass loss due to the production of gas. This resulted in a greater mass instead or mass is lesser than actual. But this can be improved by instead of using a beaker for this reaction to happen, use a conical flask and cover the mouth with cotton wool to absorb the solution spray.

Another is the inconsistent size of grinded eggshell. This is a type of random error. Small sizes will lead to faster rate of reaction and larger size will lead to slower reaction. The unreacted will affect the volume of HCl in excess. Use a machine to do the grinding to have a more consistent size.

A source of error is wind draft. This is a random error. The wind draft may cause the reading mass of eggshell to be higher or lower than actual. Improvement can be done by switching the fan off or surround the weighing balance with cardboard.

Another source of error is the sensitivity of the weighing balance. This is a type of random error. It may cause the reading to be lower or higher than the actual mass of the eggshells. An improvement can be done by using a mass balance with greater precision that can read up to 0.001g.

Retention of HCl in measuring cylinder when it is transferred into the beaker is also another source of error. This is a type of systematic error. Retention may cause the volume of HCl reacted with CaCO_3 in eggshell to be lesser than 50〖cm〗^3, thus causing the concentration of dilution with distilled water to be inaccurate. This can be improved by using the burette to dispense HCl directly into the volumetric flask.

Another source of error is that it is unknown whether all the CaCO_3 in eggshell to be lower than the actual. This can be improved by letting the reaction last longer and more stirring to promote reaction.


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