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------------------------------------------------ A chemist weighed out ? of potassium. Calculate the number of moles of potassium she weighed out. Be sure your answer has the correct number of significant digits.

A. 39.1 g
B. 1.00 g
C. 22.99 g
D. 16.0 g

To calculate the number of moles of potassium from a given mass, divide the mass by the molar mass of potassium, 39.10 g/mol, ensuring the result has the correct number of significant digits.

Explanation:

The student asks how to calculate the number of moles of potassium from a given mass. To calculate the number of moles, one would divide the mass of potassium by its molar mass. Since the molar mass of potassium is 39.10 g/mol, if the chemist weighed out 39.1 g of potassium (option A), the number of moles would be exactly 1.00 mol because 39.1 g ÷ 39.10 g/mol = 1.00 mol. Similarly, for option B (1.00 g), one would expect the moles to be 1.00 g ÷ 39.10 g/mol ≈ 0.0256 mol. For option C (22.99 g) the calculation is 22.99 g ÷ 39.10 g/mol ≈ 0.588 mol, and for option D (16.0 g) it is 16.0 g ÷ 39.10 g/mol ≈ 0.409 mol. In each case, divide the mass of potassium by the molar mass to find the moles, respecting the significant digits provided in each measurement.