Determine the number of atoms in 41.0 grams of calcium, Ca. (The mass of one mole of calcium is 40.08 g.)

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6.15 × 10²⁴

Explanation:

To find the number of atoms, divide the mass of calcium (m) by its molar mass (MM). This will give you the number of moles of calcium (n).

           Start with a formula

            Substitute values from the question

            Simplify

                Cancel out the units "g"

         Number of moles of calcium, with 4 significant figures

Then, multiply the number of moles of calcium (n) by Avogadro's number () to find the number of calcium atoms.

     Start with a formula

     Substitute values from the question

          Simplify

    Cancel out the units "mol"

                  Multiply, leave one extra digit to help round. "4" tells you to round down.

                    Final answer to 3 significant figures*

*When multiplying and dividing numbers, your final answer will have the same number of significant figures as the number with the least number of significant figures in the question.

40.08 has 4 significant figures. 41.0 has 3 significant figures. So, you want 3 significant figures in your final answer.

I hope this helps!

Learn more about Avogadro's number here:

Check out another answer that uses significant figures: