AP CHEMISTRY HELP AGAIN?

Question

I am having a lot of trouble with this problem. Could someone help me find an answer and explain why the answer is correct and how you got there?

The question is:

A sample of dolomitic limestone containing only CaCO3 and MgCO3 was analyzed.

a) When a 0.2800 gram sample of this limestone was decomposed by heating, 75.0 milliliters of CO2 at 750 mm Hg and 20 degrees C were evolved. How many grams of CO@ were produced

b) Write equations for the decomposition of BOTH carbonates described above.

c) It was also determined that the initial sample contained 0.0448 grams of calcium. What percent of the limestone by mass was CaCO3

d) How many grams of the magnesium-containing product were present in the sample in (a) after it had been heated?

I really need help with C and D....

I have got and understand A and B

could someone please help me with an answer and explanation of how you got the answer.

Thank you soooo much!!!!

Answer 1

c) It was also determined that the initial sample contained 0.0448 grams of calcium.

use molar masses to convert  the grams of Ca into grams of CaCO3:

0.0488 g Ca @ 100. g CaCO3 /40.0 g Ca  = 0.122 grams CaCO3

What percent of the limestone by mass was CaCO3:

0.122 g CaCO3 / 0.2880 gram sample  times 100 =

kyour answer: 42.36% CaCO3

======================================...

d) How many grams of the magnesium-containing product were present in the sample in (a) after it had been heated?

0.2800 grams total - 0.122 g CaCO3 = 0.166 g MgCO3

now use the ratio of 1 MgCO3 (84.32 g/mol)  -->1 MgO (40.30 g/mol) residue to convert the g MgCO3 into MgO:

0.166 g MgCO3 @ 40.30 g MgO / 84.32 g MgCO3;

your answer: 0.0793 grams ofMgO residue