eggshell experiment

Introduction

The major component of eggshells is calcium carbonate (CaCO3). Calcium carbonate cannot be dissolved in water, but can dissolve in an acid using the reaction:

2HCl(aq)+CaCO3(s) Ca2+(aq)+CO2(g)+H2O+2HCl-(aq)

This reaction is not used to titrate the CaCO3 because it is very slow when the reaction is close to the endpoint. Instead adding an excess of acid to dissolve all of the CaCO3 and then titrating the remaining H3O+ with NaOH solution can achieve the determination of the amount of acid, which has not reacted with the calcium carbonate. There are differences between amount of the acid (HCl) added and the amount left over after the reaction is equal to the amount used by the CaCO3. The reaction used to determine the leftover acid is:

HCl (aq) + NaOH (aq) H2O + Na+ (aq) + Cl- (aq)

Aim

To measure the percent by mass of CaCO3 in an eggshell.

Variables

Independent variables: Mass of calcium carbonate in eggshell.
The mass of calcium carbonate in the egg shell will be constant as the shell is taken form one egg itself.
Dependent variables: Number of moles of hydrochloric acid used.
The number of moles of that reacts with the calcium carbonate will vary according to the mass of calcium carbonate that is present in eggshell.
Control variable: Concentration of sodium hydroxide.
The concentration of NaOH is used for titration is kept constant this will give the accurate measurements of the amount of HCl that did not react with the calcium carbonate.

Apparatus

Mortar and Pestle
Standard Lab Balance
Hot Plates
200ml beaker
Measuring cylinder (10ml, 100ml)
Pipette
Burette
Conical Flask
Bunsen burner

Any reagents used in this experiment

Eggshell
NaOH 1moldm3
HCl 1moldm3
Phenolphthalein

Procedure

1. Each student should obtain one egg and the necessary glassware from the side bench.
2. Break the egg into a beaker. Add water to the egg and stir before pouring down the drain.
3. Wash the shell with deionized water and peel off all of the