HESI A2 Chemistry Practice Test

To determine the molar mass of water (H2O), it is essential to consider the atomic masses of its constituent elements. Water consists of two hydrogen atoms and one oxygen atom.

The atomic mass of hydrogen is approximately 1.01 g/mol. Since there are two hydrogen atoms in water, the contribution from hydrogen is calculated as follows:

2 × 1.01 g/mol = 2.02 g/mol.

Next, the atomic mass of oxygen is approximately 16.00 g/mol.

Now, adding the contributions from both hydrogen and oxygen gives:

2.02 g/mol (from hydrogen) + 16.00 g/mol (from oxygen) = 18.02 g/mol.

This calculation confirms that the approximate molar mass of water is indeed 18.02 g/mol, making it the correct answer. Understanding how to calculate molar mass by summing the contributions from each element in a compound is crucial in chemistry, as it applies to various substances beyond just water.