A 0.5215 gram sample of CaCO3 is dissolved in 12M HCl and the resulting solution is diluted to 250.0 mL in a volumetric flask.

How many moles of CaCO3 are used?

2 answers

grams/molar mass = moles. How many moles "were used" I don't know? How many mL did you use of the 250.
Moles used = moles in flask x (mL used/250) = ??
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