Gravimetric Assignment: Determine the percentage by mass calcium carbonate in the egg shells ????
The strength of the eggshell of birds is determined by the calcium carbonate, CaCO3, content of the eggshell. The percentage calcium carbonate in the eggshell can be determined by gravimetric analysis. A 0.439-g sample of clean, dry eggshell was completely dissolved in a minimum volume of dilute hydrochloric acid. An excess of a basic solution of ammonium oxalate, (NH4)2C2O4, was then added to form crystals of calcium oxalate monohydrate, CaC2O4.H2O. The suspension was filtered, and the crystals were then dried to constant mass; 0.570 g of CaC2O4.H2O was collected.
Determine the percentage by mass calcium carbonate in the egg shells.
Provide your answer to one place after the decimal and without units.
The strength of the eggshell of birds is determined by the calcium carbonate, CaCO3, content of the eggshell. The percentage calcium carbonate in the eggshell can be determined by gravimetric analysis. A 0.439-g sample of clean, dry eggshell was completely dissolved in a minimum volume of dilute hydrochloric acid. An excess of a basic solution of ammonium oxalate, (NH4)2C2O4, was then added to form crystals of calcium oxalate monohydrate, CaC2O4.H2O. The suspension was filtered, and the crystals were then dried to constant mass; 0.570 g of CaC2O4.H2O was collected.
Determine the percentage by mass calcium carbonate in the egg shells.
Provide your answer to one place after the decimal and without units.
1 Answer
With these problems you usually have to work backwards.
Eggshell containing
#"CaCO"_3(s) rightleftharpoons "Ca"^(2+)(aq) + "CO"_3^(2-)(aq)#
By Le Chandelier's principle, the equilibrium will shift towards the solid in acidic solution.
#"CaCO"_3(s) + 2"H"^(+)(aq) -> "Ca"^(2+)(aq) + "CO"_2(g) + "H"_2"O"(l)#
Excess
#"C"_2"O"_4^(2-)(aq) + "Ca"^(2+)(aq) + "H"_2"O"(l) stackrel("base"" ")(->) "CaC"_2"O"_4cdot"H"_2"O"(s)#
and the crystals of the monohydrate then formed due to the more basic solution decreasing the solubility of
Here we have that
From the mass of dry
The dry mass collected, assuming
#"0.570 g CaC"_2"O"_4cdot"H"_2"O" xx ("100.0869 g/mol CaCO"_3)/("146.112 g/mol CaC"_2"O"_4cdot"H"_2"O")#
#= "0.391 g CaCO"_3#
Therefore, the percent by mass is:
#("0.391 g CaCO"_3(s))/("0.439 g eggshell") xx 100% = color(blue)(88.9% "w/w CaCO"_3)#
