What is the number of moles in a 78.8-gram sample of MgCO3 (gram-formula mass 84.3 g/mol)?

June 2023 NY Regents Chemistry Exam

37 What is the number of moles in a 78.8-gram sample of MgCO3 (gram-formula mass 84.3 g/mol)?
(1) 0.949 mol

(2) 0.935 mol

(3) 0.843 mol

(4) 1.070 mol

Solution: Table T on the Reference Table gives the equation for calculating moles which is number of moles = given mass/ gram formula mass. All we need to do is to plug our values in.

Moles = 78.8g/84.3 g/mol

Answer: 2

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