a straightforward quantitative chemistry problem

[Maggieee]

Hey guys,

I have a quite stupid question. I can ask it when the school begins next year but I can't wait for the solution. 

It will be awesome if you could explain the process to me step-by-step.

Thanks

 

here is the question

 

A student wished to determine the percentage by mass of calcium carbonate in an eggshell. She reacted 3.953g of the eggshell with 50cm3 of 1.00moldm-3 hydrochloric acid. After all the shell had reacted, the resulting solution was placed in a volumetric flask and the volume made up to 100cm3. 10.0 cm3 of this soluiton reacted exactly with 12.65cm3 of 0.100moldm-3 sodium hydroxide solution, NaOH(aq). Calculate the percentage by mass of calcium carbonate in the eggshell.

Edited December 21, 2014 by Maggieee

[Baller97]

Hey guys,

I have a quite stupid question. I can ask it when the school begins next year but I can't wait for the solution. 

It will be awesome if you could explain the process to me step-by-step.

Thanks

 

here is the question

 

A student wished to determine the percentage by mass of calcium carbonate in an eggshell. She reacted 3.953g of the eggshell with 50cm3 of 1.00moldm-3 hydrochloric acid. After all the shell had reacted, the resulting solution was placed in a volumetric flask and the volume made up to 100cm3. 10.0 cm3 of this soluiton reacted exactly with 12.65cm3 of 0.100moldm-3 sodium hydroxide solution, NaOH(aq). Calculate the percentage by mass of calcium carbonate in the eggshell.

# mol NaOH = MV = 0.100 x 0.01265 = 0.001265 mol NaOH

now # mol NaOH will be same as # mol HCl left after reacting with the eggshell. So excess mol HCl is 0.001265

# mol HCl you start with = 1 x 0.050 = 0.050 mol HCl

so

# mol HCl reacted = 0.050 - 0.001265 = 0.048735 mol HCl reacted

now 1 mol CaCO3 reacts with 2 mol HCl

so # mol CaCO3 = 0.048735/2 = 0.02437 mol CaCO3

now from molar mass of CaCO3 find mass of CaCO3 in the sample and calculate the percent in the sample