A water molecule is made up of one oxygen atom and two hydrogen atoms. What is the mass of one mole of water? How many atoms of oxygen and hydrogen are there in one mole of water?
The Correct Answer and Explanation is:
Correct Answer:
- Mass of one mole of water (H₂O):
The molar mass of water is 18 grams per mole. - Number of atoms in one mole of water:
- Oxygen atoms: 1 mole of water contains 1 mole of oxygen atoms, which is 6.022 × 10²³ atoms.
- Hydrogen atoms: 1 mole of water contains 2 moles of hydrogen atoms, which is 2 × 6.022 × 10²³ = 1.204 × 10²⁴ atoms.
Explanation:
A single water molecule is composed of two hydrogen atoms and one oxygen atom. Chemically, it is represented as H₂O. To find the mass of one mole of water, we need to calculate its molar mass by summing the atomic masses of hydrogen and oxygen.
- The atomic mass of hydrogen (H) is approximately 1 gram per mole.
- The atomic mass of oxygen (O) is approximately 16 grams per mole.
Since water has two hydrogen atoms and one oxygen atom, the molar mass of water is:
2(1) + 16 = 18 grams per mole
This means one mole of water weighs 18 grams.
Now, using Avogadro’s number, which is 6.022 × 10²³, we can determine how many individual atoms are in one mole of water molecules.
- Each water molecule has 1 oxygen atom, so one mole of water contains 6.022 × 10²³ oxygen atoms.
- Each water molecule also has 2 hydrogen atoms, so one mole of water contains 2 × 6.022 × 10²³ = 1.204 × 10²⁴ hydrogen atoms.
This calculation helps us understand the massive scale of particles even in small amounts of substances. Despite being only 18 grams, a mole of water contains over 10²⁴ atoms, which shows the atomic world operates on a scale that is very different from what we see in everyday life.
