Solution - Finding a molecular mass
Other Ways to Solve
Finding a molecular massStep-by-step explanation
1. Break down the molecule to its elements
The molecule Ca(OH)2 consists of:
1 Calcium atom
2 Oxygen atoms
2 Hydrogen atoms
| Element | Symbol | # of atoms |
| Calcium | Ca | 1 |
| Oxygen | O | 2 |
| Hydrogen | H | 2 |
2. Identify the atomic mass of each element
The atomic mass is shown below each element on the periodic table.
Ca(OH)2 molecules consist of:
Calcium Ca=40.078 u
Oxygen O=15.9994 u
Hydrogen H=1.00794 u
| Element | Symbol | Atomic mass | # of atoms |
| Calcium | Ca | 40.078 | 1 |
| Oxygen | O | 15.9994 | 2 |
| Hydrogen | H | 1.00794 | 2 |
3. Calculate the total atomic mass of each element in a molecule of Ca(OH)2
Ca → 1·40.078=40.078 u
O2 → 2·15.9994=31.9988 u
H2 → 2·1.00794=2.01588 u
| Element | Symbol | Atomic mass | # of atoms | Total atomic mass |
| Calcium | Ca | 40.078 | 1 | 40.078 |
| Oxygen | O | 15.9994 | 2 | 31.9988 |
| Hydrogen | H | 1.00794 | 2 | 2.01588 |
4. Calculate the mass of the molecule Ca(OH)2
40.078+31.9988+2.01588=74.09268
The average molecular mass of Ca(OH)2 is 74.09268 u.
5. Graph of molecular composition by atoms
6. Graph of molecular composition by mass
Why learn this
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Every physical thing in the world is made up of matter. Whether it is the air we breathe, the food we eat, or the gas we use to heat our homes, almost everything that exists is made up of matter, and all matter is made up of molecules. Because of this, understanding the properties of molecules can help us better understand the concepts that explain the world around us, such as why different materials behave as they do. Molecular mass is also an important concept for anyone interested in pursuing a career in certain STEM fields.