What is the molar mass of calcium oxide?
(a) 40.08
(b) 56.08
(c) 72.15
(d) 16.00
The Correct Answer and Explanation is:
The correct answer is (a) 56.08 g/mol.
Explanation:
To determine the molar mass of calcium oxide (CaO), we need to add the molar masses of calcium (Ca) and oxygen (O), as calcium oxide is composed of one calcium atom and one oxygen atom.
Step 1: Find the molar mass of calcium (Ca)
- The atomic number of calcium is 20, and the atomic mass of calcium is approximately 40.08 g/mol. This means one mole of calcium weighs 40.08 grams.
Step 2: Find the molar mass of oxygen (O)
- Oxygen has an atomic number of 8, and its atomic mass is 16.00 g/mol. This means one mole of oxygen weighs 16.00 grams.
Step 3: Add the atomic masses of calcium and oxygen
- The molar mass of calcium oxide (CaO) is calculated by adding the atomic masses of calcium (Ca) and oxygen (O):
[
\text{Molar mass of CaO} = 40.08 \, \text{g/mol} (\text{Ca}) + 16.00 \, \text{g/mol} (\text{O}) = 56.08 \, \text{g/mol}
]
Thus, the molar mass of calcium oxide is 56.08 g/mol.
Why the other answers are incorrect:
- (b) 56.08 is the correct answer, as it corresponds to the sum of the molar masses of calcium and oxygen.
- (c) 72.15 is incorrect because it exceeds the actual molar mass of calcium oxide. This could be mistaken by adding the mass of other compounds.
- (d) 16.00 is only the molar mass of oxygen, not calcium oxide.
In summary, the molar mass of calcium oxide is 56.08 g/mol, which is calculated by adding the molar masses of calcium (40.08 g/mol) and oxygen (16.00 g/mol).