[lucas123]

Hello there, I have a percent composition lab involving the percent of calcium carbonate in seashells and I would like some help in figuring out how i calculate that percentage. I've recorded mass of the seashell and the initial/final NaOH that i have used in the lab. My teacher gave us a page that said calculations and it reads:

"for this lab, all you need is the volume of NaOH in ml. let V be that volume and let m be the mass of calcium carbonate in mg. The mass is given by : m = 50 - 5v "

how would i use this formula with the numbers i have recorded? for example i have 50mg of shell and the initial NaOH i have is 10ml of a 0.1M solution and the final NaOH i have is 20ml of the 0.1M solution.

thanks you for your help it's much appreciated

[Borek]

Start writing equations for all reactions that took place. It is all in a simple stoichiometry.

Also, compare http://www.titrations.info/titration-calculation