# determine the mass of calcium carbonate in chicken eggshells and hence its percentage by mass

Topics: Observational error, Measurement, Calcium carbonate Pages: 4 (771 words) Published: July 5, 2014
Aim: determine the mass of calcium carbonate in chicken eggshells and hence its percentage by mass

ApparatusUncertainty
25.00 cm3 pipette
± 0.03 cm3
50.00 cm3 burette
± 0.05 cm3
± 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
± 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 %
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...