What is the number of moles of KF in a 29-gram sample of the compound?

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.

K=39 g/mol

F= 19 g/mol

Gram formula mass of KF = 39+19 = 58g/mol

Number of moles = 29g/58g/mol= 0.50 mol

Answer: 3

Prepare for the Chemistry Regents Exam: HERE