January 2018 NY Regents Chemistry Exam
36 What is the number of moles of KF in a 29-gram sample of the compound? (1) 1.0 mol
(2) 2.0 mol
(3) 0.50 mol
(4) 5.0 mol
Solution: Table T on the Reference Table shows the formula for mole calculations.
Number of moles = given mass/ gram-formula mass.
Let's first find the gram formula mass of KF. We need to find the mass of K and F on the Periodic table.
F= 19 g/mol
Gram formula mass of KF = 39+19 = 58g/mol
Number of moles = 29g/58g/mol= 0.50 mol
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