Answer: option (3) SrO, with 84.56%
Explanation:
You have to calculate the mass of strontium and the mass of the compound, for each of the four compounds, and compute the percent:
percent of strontium = (mass of strontium / mass of the chemical formula) × 100 %.
These are the atomic masses of the elements that you have to use:
Atomic mass of Sr: 87.62 g/mol
Atomic mass of Cl: 35.453 g/mol
Atomic mass of I: 126.904 g/mol
Atomic mass of O: 15.999 g/mol
Atomic mass of S: 32.065 g/mol
(1) SrCl₂:
i) mass of Sr: 87.62 g/mol
ii) mass of Cl₂: 2×35.453 g/mol = 70.906 g/mol
iii) mass of SrCl₂: 87.62 g/mol + 70.906 g/mol = 158.526 g/mol
iv) Sr % = [87.62 / 158.526 ] × 100 = 55.27%
(2) SrI₂
Following the same procedure:
i) Sr % = [87.62 / (87.62 + 2× 126.904) ] × 100 = 25.66%
(3) SrO
i) Sr % = [87.62 / (87.62 + 15.999) ] × 100 = 84.56%
(4) SrS
i) Sr % = [87.62 / (87.62 + 32.065) ] × 100 = 73.21%
