Posted by Anonymous on .
the recommended daily allowance of calcium is 1.2 g. calcium carbonate contains 12.0 % calcium by mass. how many grams of calcium carbonate are needed to provide the rda of calcium

chemistry 
DrBob222,
I have news for you. CaCO3 is 40% by mass Ca and not 12.0%. (Actually 40.04%).
So if you want 1.2 g you would take
0.40x = 1.2 and x = 1.2/0.4 = 3.0 g CaCO3.
But your problem is worked the same way.
0.12x = 1.2 and x = 10 g. Check your figures. I can assure that CaCO3 is 40% Ca and not 12%.