Final answer:
To calculate the number of atoms in a sample of Sr, divide the mass of the sample by the molar mass of Sr, then multiply by Avogadro's number. In this case, the number of atoms is 4.6 x 10^20 atoms.
Step-by-step explanation:
To calculate the number of atoms in a sample of Sr, we need to use the mole concept and Avogadro's number. First, convert the mass of the sample to moles by dividing it by the molar mass of Sr. The molar mass of Sr is 87.62 g/mol. Next, multiply the number of moles by Avogadro's number (6.022 x 10^23 atoms/mol) to get the number of atoms. In this case, the mass of the sample is 67.5 mg, which is equal to 0.0675 g.
To convert grams to moles, divide the mass by the molar mass:
0.0675 g / 87.62 g/mol = 7.7 x 10^-4 mol
Finally, multiply the number of moles by Avogadro's number to get the number of atoms:
7.7 x 10^-4 mol * 6.022 x 10^23 atoms/mol = 4.6 x 10^20 atoms