Question

2) Calculate the percentage by mass of the element shown in the following substances. a) b) c) d) e) Al in Al₂O3 O in H₂SO4 N in NH4NO3 O in Al(NO3)3 C in C4H10 f) Cu in CuSO4 g) H in H₂SO4 h) O in CuSO4.5H2O​

Answer 1

To calculate the percentage by mass of an element in a compound, determine the molar mass of the compound, find the mass of the element in one formula unit, divide this by the molar mass of the compound, and multiply by 100 to obtain the percentage. For aluminum in Al₂O₃, this gives 52.94%.

Step-by-step explanation:

To calculate the percentage by mass of an element in a compound, you follow these steps:

1. Write down the chemical formula of the compound.
2. Find the molar mass of the compound by summing the atomic masses of all the atoms in the formula.
3. Determine the collective mass of the given element in one formula unit of the compound.
4. Divide the mass of the element by the molar mass of the entire compound and multiply by 100 to get the percentage.

For example, to calculate the percentage by mass of aluminum (Al) in aluminum oxide (Al₂O₃), you would:

1. Write down the formula: Al₂O₃.
2. Calculate the molar mass: 2×26.98 (Al) + 3×16.00 (O) = 101.96 g/mol.
3. Find the mass of Al in the formula: 2×26.98 g/mol = 53.96 g/mol.
4. Divide and multiply by 100: (53.96 / 101.96) × 100 = 52.94%.

Therefore, the correct option for aluminum in Al₂O₃ is 52.94% by mass.