Chemistry Regents Practice Test

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What is the percent composition by mass of sulfur in the compound MgSO4 (gram-formula mass = 120. grams per mole)?

The correct answer is: 27%

To calculate the percent composition by mass of sulfur in magnesium sulfate (MgSO4), you first need to identify the molar masses of the individual elements in the compound. The compound comprises magnesium (Mg), sulfur (S), and oxygen (O). 1. The molar mass of magnesium (Mg) is approximately 24.3 g/mol. 2. The molar mass of sulfur (S) is approximately 32.1 g/mol. 3. The molar mass of oxygen (O) is approximately 16.0 g/mol. Since there are four oxygen atoms in the compound, you multiply this value by four, giving you 64.0 g/mol for oxygen. Now, you can calculate the total molar mass of MgSO4: - Molar mass of Mg = 24.3 g/mol - Molar mass of S = 32.1 g/mol - Molar mass of O (4 × 16.0 g/mol) = 64.0 g/mol Adding these together: 24.3 g/mol (Mg) + 32.1 g/mol (S) + 64.0 g/mol (O) = 120.4 g/mol Since the question states the