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When a vitamin or supplement claims, for example, that it contains

600 mg of calcium (as calcium carbonate)

what does that mean? Does each tablet contain 600 milligrams of the element calcium?

Or does a tablet contain 600 milligrams of the compound calcium carbonate? In that case, using the molar masses of Ca and CaCO3, each tablet would contain only

600 * (40.1 / 100.1) = 240.4 milligrams of the element calcium.

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    $\begingroup$ It means it has calcium carbonate sufficient to provide 600 mg of calcium. Since chalk is 40% calcium, the mass of chalk is 2.5 times 600 mg = 1.5 g. $\endgroup$ – Ed V Aug 21 '19 at 1:46
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    $\begingroup$ Otherwise, there would be written "600 mg of calcium carbonate". $\endgroup$ – Poutnik Aug 21 '19 at 3:48
  • $\begingroup$ Similarly, 600 Euros ( in dollars ) does not mean 600 dollars, but 600 Euros exchanged into the equivalent number of dollars. $\endgroup$ – Poutnik Aug 22 '19 at 1:40

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