Question

A chemist weighed out 57.4 g of calcium. Calculate the number of moles of calcium she weighed out. Round your answer to 3 significant digits.

a. 2.45 moles
b. 2.90 moles
c. 1.38 moles
d. 5.42 moles

Answer 1

To calculate the number of moles of calcium from the given mass, divide the mass (57.4 g) by the molar mass of calcium (40.08 g/mol). The result is approximately 1.43 moles, which is closest to option c, 1.38 moles.

Step-by-step explanation:

To calculate the number of moles of calcium weighed, you can use the formula:


Number of moles = Mass in grams ÷ Molar mass of the element (in g/mol)

The molar mass of calcium (Ca) is 40.08 g/mol. Thus, the number of moles of 57.4 g of calcium is calculated as follows:


57.4 g ÷ 40.08 g/mol = 1.432 moles of calcium, which, rounded to three significant digits, is 1.43 moles.

Therefore, the correct answer is:

c. 1.38 moles