eggshell
Determination of Calcium Carbonate in Eggshells – Background
The major component of eggshells is calcium carbonate, CaCO3(s). This analysis is done volumetrically by using a characteristic reaction of carbonate compounds, namely their reaction with acids. Calcium carbonate (limestone) is very insoluble in pure water but readily reacts in acid according to the reaction below.
2HCl(aq) + CaCO3(s) → CaCl2(aq) + CO2(g) + H2O(l) + HCl(aq)
(in excess)
(limiting reagent)
(1)
(unreacted)
This reaction cannot be used directly to titrate the CaCO3 because it is very slow when the reaction is close to the endpoint. Instead the determination is achieved by adding an excess of hydrochloric acid to react with all of the CaCO3 and then titrating the remaining unreacted HCl with NaOH solution to determine the amount of acid which did not react with the calcium carbonate. The difference between the moles of the acid (HCl) initially added and the moles of
HCl left unreacted after the reaction, is equal to the moles of HCl that did react with CaCO3.
The reaction used to determine the amount of unreacted acid by titration is given below. This type of analysis is generally referred to as a back-titration.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
(2)
(unreacted)
Calculations:
The purpose and goal of today's experiment is to determine the mass percent of CaCO3 in an eggshell. The following logic stream may be helpful to understand how you will reach that goal. The calculation steps are reproduced at the end of the written procedure in a more formal step-by-step manner. As with all calculations, make sure to show all units and pay close attention to significant figures.
CaCO3 in an Eggshell - Background
B-1
Pre-Lab Homework
1. How many milliliters of 0.383 M HCl are needed to react with 16.2 g of CaCO3?
2HCl(aq) + CaCO3(s) → CaCl2(aq) + CO2(g) + H2O(l)
2. If a 45.0 g sample of CaCO3 (s) is added to 1.25 L HCl (aq) that has a density of
The major component of eggshells is calcium carbonate, CaCO3(s). This analysis is done volumetrically by using a characteristic reaction of carbonate compounds, namely their reaction with acids. Calcium carbonate (limestone) is very insoluble in pure water but readily reacts in acid according to the reaction below.
2HCl(aq) + CaCO3(s) → CaCl2(aq) + CO2(g) + H2O(l) + HCl(aq)
(in excess)
(limiting reagent)
(1)
(unreacted)
This reaction cannot be used directly to titrate the CaCO3 because it is very slow when the reaction is close to the endpoint. Instead the determination is achieved by adding an excess of hydrochloric acid to react with all of the CaCO3 and then titrating the remaining unreacted HCl with NaOH solution to determine the amount of acid which did not react with the calcium carbonate. The difference between the moles of the acid (HCl) initially added and the moles of
HCl left unreacted after the reaction, is equal to the moles of HCl that did react with CaCO3.
The reaction used to determine the amount of unreacted acid by titration is given below. This type of analysis is generally referred to as a back-titration.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
(2)
(unreacted)
Calculations:
The purpose and goal of today's experiment is to determine the mass percent of CaCO3 in an eggshell. The following logic stream may be helpful to understand how you will reach that goal. The calculation steps are reproduced at the end of the written procedure in a more formal step-by-step manner. As with all calculations, make sure to show all units and pay close attention to significant figures.
CaCO3 in an Eggshell - Background
B-1
Pre-Lab Homework
1. How many milliliters of 0.383 M HCl are needed to react with 16.2 g of CaCO3?
2HCl(aq) + CaCO3(s) → CaCl2(aq) + CO2(g) + H2O(l)
2. If a 45.0 g sample of CaCO3 (s) is added to 1.25 L HCl (aq) that has a density of