Calculate the percentage by mass of oxygen in the following compounds: (f) penicillin, C₁₆H₁₈N₂O₄S.

Verified step by step guidance

1. Determine the molar mass of each element in the compound. For penicillin (C16H18N2O4S), calculate the molar mass of carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and sulfur (S).
2. Multiply the atomic mass of each element by the number of atoms of that element in the compound. For oxygen in penicillin, multiply the atomic mass of oxygen by 4, as there are 4 oxygen atoms in the formula C16H18N2O4S.
3. Add the total masses from step 2 for all elements in the compound to find the molar mass of penicillin.
4. Calculate the mass percentage of oxygen by dividing the total mass of oxygen (from step 2) by the molar mass of penicillin (from step 3).
5. Multiply the result from step 4 by 100 to convert it to a percentage. This will give you the percentage by mass of oxygen in penicillin.

Key Concepts

Molar Mass Calculation

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). To calculate the molar mass of a compound, sum the atomic masses of all the atoms in its molecular formula. For penicillin (C16H18N2O4S), this involves adding the molar masses of carbon, hydrogen, nitrogen, oxygen, and sulfur based on their respective quantities in the formula.

Percentage by Mass

Percentage by mass is a way to express the concentration of a particular element in a compound. It is calculated by dividing the mass of the element in one mole of the compound by the total molar mass of the compound, then multiplying by 100. This provides a clear understanding of how much of the compound's mass is contributed by a specific element, such as oxygen in penicillin.

Empirical and Molecular Formulas

The empirical formula represents the simplest whole-number ratio of elements in a compound, while the molecular formula shows the actual number of each type of atom in a molecule. Understanding the difference is crucial when calculating mass percentages, as the molecular formula (C16H18N2O4S) provides the exact composition needed for accurate molar mass and percentage calculations.