The chemical formula for calcium hydroxide is: Ca(OH)2. Calculate the molar mass of calcium hydroxide. Round your answer to 2 decimal places.
The Correct Answer and Explanation is:
74.09
Explanation
The molar mass of a compound is the mass of one mole of that substance, expressed in units of grams per mole ( g/mol ). To calculate the molar mass of calcium hydroxide, Ca(OH)₂, we need to sum the atomic masses of all the atoms in its chemical formula.
First, we must identify the elements and the number of atoms of each in the formula. The formula Ca(OH)₂ breaks down as follows:
- Ca (Calcium): There is one atom of calcium.
- (OH)₂ (Hydroxide): The subscript ‘2’ outside the parentheses applies to both the oxygen and hydrogen atoms inside. This means there are two oxygen (O) atoms and two hydrogen (H) atoms.
Next, we find the standard atomic mass of each element from the periodic table:
- Atomic mass of Calcium (Ca) ≈ 40.078 g/mol
- Atomic mass of Oxygen (O) ≈ 15.999 g/mol
- Atomic mass of Hydrogen (H) ≈ 1.008 g/mol
Now, we multiply the atomic mass of each element by the number of atoms of that element present in the compound and then sum the results.
- Mass from Calcium: 1 atom × 40.078 g/mol = 40.078 g/mol
- Mass from Oxygen: 2 atoms × 15.999 g/mol = 31.998 g/mol
- Mass from Hydrogen: 2 atoms × 1.008 g/mol = 2.016 g/mol
Finally, we add these values together to find the total molar mass of calcium hydroxide:
Molar Mass = 40.078 g/mol + 31.998 g/mol + 2.016 g/mol = 74.092 g/mol .
The problem asks for the answer to be rounded to two decimal places. The calculated value is 74.092. Since the third decimal digit (2) is less than 5, we round down, which means the second decimal digit remains unchanged. Therefore, the molar mass of calcium hydroxide is 74.09 g/mol .
