IB Chemistry IA Eggshell Lab

CaCO3 in an Eggshell An investigation determining the percentage by mass of calcium carbonate in an eggshell.

Ms. Mass Nour Makarem 12S-JM Thursday, January 19th, 2017

Introduction Calcium Carbonate (CaCO3) is an abundant simple chemical compound, with a hexagonal crystal structure. Occurring readily in nature it is found in limestone and rocks.The compound yields extensive industrial and medical applications. A carbon based compound, leading to potential prevalence in organic life, particularly that of the egg shells of chicken eggs. The colour difference can be attributed to breed of the chicken. There is no distinct relationship between colour and quality of egg, meaning nutritional value & taste do not differ from colour to colour. Most notable however is the price and size difference. Brown eggs tend to be larger, since they are made by larger hens and hence are priced slightly more expensively. The implicit reason behind the price increase can be attributed to the dietary needs of the chicken required to produce a larger egg. A larger hen needs more food, within its diet presumably there must be more calcium, leading to the assumption that brown eggs hold more CaCO3. On average, high quality eggs contain 2.2 grams of calcium in the form of calcium carbonate. Approximately 94% of a dry eggshell is calcium carbonate and has a typical mass of 5.5 grams. The aim of the investigation deduce the relationship present between percentage composition of CaCO3 in eggshells with the colour of the eggshell. The following is an equation of the reaction taking place: CaCO3 (s) + 2HCl(aq) → CaCl2 (aq) + CO2 (g) + H2O(l)

Research Question What is the relationship between the eggshell colour (white & brown) and calcium carbonate percentage composition?

Hypothesis Experiment hypothesis H1: If the brown eggshell is ground to a thin powder and mixed with hydrochloric acid to form a solution that undergoes a back titration with sodium hydroxide, then the result of the titration will reveal a higher percentage mass composition of CaCO3. This is because the brown eggshells correspond to larger chickens which presumably have a higher dietary calcium intake.

Materials • • • • • • • •

1x [0.6g] Brown Eggshells. 1x [0.6g] White Eggshells. 1x Pestle & Mortar. 1x Conical Flask [250 ml]. 1x White Tile. 1x Volumetric Flask [100 ml]. 10x 1 ml Phenolphthalein. 1x Stirrer.

• • • • • • • •

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1x Digital Scale. 1x 5 ml Pipette. 1x Beurette. 1x Graduated Pipette (w/ sucker) 1x Beurette Stand. 10x 20.0 cm3 of (1 mol dm-3) HCl. 10x 20.0 cm3 of Distilled Water. 1x 100.0 cm3 NaOH.


(±0.01 g) (±0.50 ml) (±0.50 ml) (±0.50 ml)

Variables Table 1.1 Table containing the independent variable and how it will be measured (the dependent variable) Independent

Dependent

Brown eggshells. White eggshells. i.e. the volume of the titrants.

The percentage by mass of CaCO3 in the eggshell.

Table 1.2 Table containing the Control variables, the reason they’re controlled and the means by which the will be controlled. Controlled: #

Variable:

Reason for Control

1 The amount of the solution used in the titration. 2 The initial volume of the solvent.

Concentration maintained.

3 The initial mass of solute. (eggshells).

Accuracy of percentage composition yielded.

Method Safety Precautions & Ethical Considerations: Eggshells can be sharp and caution must be taken in order to avoid skin penetrations. The use of organic eggshells requires the sacrifice of potential food. When handling acids take precaution due to their corrosive properties. Wash hand thoroughly if contact is made. Part I - Solution Preparation 1. Begin by acquiring either a brown or white eggshell. Attentively wash the shell of the egg to remove any dirt and organic mater. 2. In order to vaporise surface liquid accumulations, apply heat in the form dry air by means of hairdryer or oven. 3. Use the pestle and mortar to grind the eggshell into as thin a powder as possible. 4. Accurately measure 0.6 grams of the eggshell powder using the scale. Then place the measure powder int a 250 ml conical flask. 5. Using a graduated pipette measure 20.0 cm3 of (1 mol dm-3) HCl. Add this acid slowly to the conical flask containing the eggshell powder. 6. Upon completion of the entire reaction, add 20.0 cm3 of Distilled Water using the graduate pipette. Take the mixture and pour it into a volumetric flask [100 cm3].

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Part II - Titration 1. Extract 10 cm3 aliquots of the prepared solution and pour it into a beaker. Add 2 ml of Phenolphthalein. 2. Use the NaOH to clean the burette. After cleaning, begin the titration procedure by clasping the burette to the stand and pouring an adequate amount of NaOH into the burette. 3. Repeat the titration procedure multiple times using more aliquots to acquire accurate amount of trials. Repeat Part I to prepare a mixture containing the white eggshell. Then proceed to to titrate it following the same prouder of Part II. Ensure all equipment is always cleaned, avoid contamination.

Raw Data Collection Table 2 Table containing raw data collected during back titrations of NaOH for both eggshells. Brown Eggshell Solution (± 0.5 cm³)

White Eggshell Solution (± 0.50 cm³)

First Titration

11.2

12.9

Second Titration

11.2

12.9

Third Titration

11.3

13.0

Fourth Titration

11.1

12.8

Fifth Titration

11.2

13.1

Average Titration Values

11.2

12.9

Volume of Aliquots (± 0.5 cm³)

10.0

10.0

1.0

1.0

Molarity of NaOH (mol)

Qualitative Data • When reacting the Eggshell powders with HCl both the brown and white eggshells produced foam. º This made it difficult to move from flask to flask, because there would be content lost in the form of residue. º The bubbles were composed of CO2. • When reaching the end point of the titration the conical flask containing the eggshell and HCl solution turned close to pink, but for it to be an accurate titration, it was not close to fuchsia.

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Data Processing Uncertainties There is first an uncertainty associated with the prepared eggshell solution. This is composed of the uncertainty of the mass of the eggshell, the volume of HCl and the volume of water used. The uncertainty of the equipment they were measured with is going to be decided with the amount measured of the substance. Multiplying the fraction (which is considered the absolute uncertainty) by 100 will yield the percentage uncertainty. For the case of this experiment the following formula can be produced:

✓

0.01 0.6

◆

⇥ 100

Eggshell Mass

+

✓

0.5 20

◆

⇥ 100

+

Volume of HCl

2

✓

0.5 40

◆

⇥ 100

=

6.67%

U ncertainty

Volume of Water

The volume of water is multiplied by two, because in order to reach 80 cm³ of water, two separate measurements of 40 cm³ needed to take place. Since the graduated pipette has a maximum volume of 50 cm³. Throughout the calculation process however uncertainties will be written and factored in.

Calculations

CaCO3 (s) + 2HCl(aq) → CaCl2 (aq) + H2O(l) + CO2 (g) 1 mole

+ 2 mole

→

1 mole + 1 mole + 1 mole

Steps 1) " Moles of Solvent (HCl) =

Volume (cm 3 ) × Concentration (mol.dm −3 ) 
 1000

2) " Moles of Titrant (NaOH) =

Volume (cm 3 ) × Concentration (mol.dm -3 ) 
 1000

3) Moles of CaCO3 within Solution = Moles of Solvent – Moles of Titrant 4) Mass of CaCO3 = Moles of CaCO3 in Solution × Molar mass CaCO3 of Eggshell

⎛

Mass of CaCO

⎞

3 5) " Percentage of CaCO 3 in eggshell = ⎜ × 100 ⎝ Mass of eggshell used ⎟⎠

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Table 3.1 Table containing calculations of percentage CaCO3 by mass for the brown eggshell.

Brown Eggshell Volume of HCl used in trials 1)

Moles of HCl used Volume of NaOH solution used

2)

Moles of NaOH used

3)

Moles of reacted HCl

4)

Moles of CaCO3

5)

Mass of CaCO3

6)

= 20 ± 0.5 cm³ = 20 cm³ ± 2.50% × 1M ±* ÷ 1000 = 0.02 moles ± 2.50 % = 11.2 ± 0.5 cm³ = 11.2 ± 0.5 cm³ × 1M ±* ÷ 1000 = 0.0112 moles ± 4.46% = 0.02 moles ± 2.50 % - 0.0112 moles ± 4.46% = 0.0088 moles ± 6.96% = 0.0088 moles ± 6.96% ÷ 2 = 0.0044 moles ± 6.96% = 0.0044 moles ± 6.96% × 100.09 g.mol-1 = 0.44 grams ± 6.96%

Percentage of CaCO3 in

= 0.44 grams ± 6.96% ÷ 0.60 grams ± 1.66% × 100

Eggshell

= 73.3% ± 8.62%

*Uncertainty value

Value is not known, mixture provided by teacher.

Table 3.2 Table containing calculations of percentage CaCO3 by mass for the white eggshell.

White Eggshell Volume of HCl Used in trials 1)

Moles of HCl used Volume of NaOH solution used

2)

Moles of NaOH used

3)

Moles of reacted HCl

4)

Moles of CaCO3

5)

Mass of CaCO3

6)

= 20 ± 0.5 cm³ = 20 cm³ ± 2.50% × 1M ±* ÷ 1000 = 0.02 moles ± 2.50 % = 12.9 ± 0.5 cm³ = 12.9 ± 0.5 cm³ × 1M ±* ÷ 1000 = 0.0129 moles ± 3.88% = 0.02 moles ± 2.50% - 0.0129 moles ± 3.88% = 0.0071 moles ± 6.38% = 0.0071 moles ± 6.38% ÷ 2 = 0.0036 moles ± 6.38% = 0.0036 moles ± 6.38% × 100.09 g.mol-1 = 0.36 grams ± 6.38%

Percentage of CaCO3 in

= 0.36 grams ± 6.38% ÷ 0.60 grams ± 1.66% × 100

Eggshell

= 60.0% ± 8.04%

*Uncertainty value

Value is not known, mixture provided by teacher.

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Conclusion It seems conclusively, based on the calculations carried out previously that as hypothesised, the Brown Eggshells have a higher percentage by mass CaCO3 than the White Eggshell. The Brown Eggshell showed a 13.3% greater CaCO3 content than the White Eggshell, since the initial eggshell mass was controlled to 0.6 ±0.01grams, it can also be said that the difference between the eggshells is 0.0798 grams. There was a difference in the uncertainties, but on average, they each yielded a 8.33% uncertainty. Evidently Brown Eggshells contain more Calcium carbonate by percentage mass than White Eggshells.

Evaluation Eggshells on average contain 94% CaCO3 content by dry mass, but there have been lowest recorded percentages of nearly 78%[1 ]. This average is posed to all varieties of eggs, meaning the average is taken of the species of the chicken, colour, and place of origin. The aim of the investigation was to deduce which colour dry eggshell had a greater Calcium carbonate content by percentage mass. In the case of the two eggshells used it would seem clear that brown eggshells contain more. This claim can not be generalised to all eggshells however. Since a theoretical yield isn’t known, percentage error can not be acquired, and thus it isn’t inherently clear wether systematic errors are more abundant than random errors. Limitations in the design

Improvement

1 Systematic Error: Using certain fragments of the ground dry eggshell.

By using only small grounded portions of the eggshell, the discretion of CaCO3 might not have been even and the ground portions used could have had an excessively high/low concentration of CaCO3 .

2 Random Error: Using Only one dry Eggshell from the same batch.

By using even more than one eggshell from different batches, the reliability of the data could be improved.

3 Random Error: Uncertainty was high due to the uncertainty of the equipments.

By using equipment with lower uncertainty values and adjusting for parallax error, the results would be more accurate.

4 Random Error: Measuring low quantities of solutions.

By measuring volumes greater than 10 cm³ aliquots, the uncertainty pretty much halves.

5 Systematic Error: Assuming all the CaCO3 had reacted.

Using more HCl.

6 Systematic Error: Not covering the conical flask during the reaction, meaning some HCl could have evaporated.

Acquiring a lid to cover the flask entirely.

7 Systematic Error: Some of the equipment was contaminated, due to poor cleaning.

Cleaning the equipment thoroughly, especially with the solutions that well be placed in them.

The data is reliable, and valid, however the conclusions can’t be expanded to a broader scope. What this means is that the data doesn’t prove the percentage mass composition for all eggshells of that colour. [1 ]

Refer to first references "7

Extension Comparing the CaCO3 mass percentage composition of Free-range organic eggs to factory eggs. This would provide an insight as to the dietary calcium intake of the chickens from either farm.

References & Bibliography 1) D. Butcher, Gary and Richard Miller. "Concepts Of Eggshell Quality". EDIS VM69 (1990): 1-2. Print.
 http://edis.ifas.ufl.edu/pdffiles/VM/VM01300.pdf

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