To determine the number of oxygen atoms in 1.8 grams of water at STP (Standard Temperature and Pressure), we need to use the concept of molar mass and Avogadro's number.
The molar mass of water (H2O) is the sum of the atomic masses of hydrogen (H) and oxygen (O). Hydrogen has an atomic mass of approximately 1 gram/mole, and oxygen has an atomic mass of approximately 16 grams/mole. Therefore, the molar mass of water is 18 grams/mole (2 grams from hydrogen + 16 grams from oxygen).
Now, we can calculate the number of moles of water in 1.8 grams:
Number of moles = Mass / Molar mass Number of moles = 1.8 grams / 18 grams/mole Number of moles = 0.1 moles
Since there is a 1:1 ratio of oxygen atoms to water molecules, the number of oxygen atoms is equal to the number of moles of water. Therefore, there are 0.1 moles of oxygen atoms in 1.8 grams of water.
Avogadro's number tells us that there are approximately 6.022 x 10^23 entities (atoms, molecules, etc.) in 1 mole of a substance. Thus, to calculate the number of oxygen atoms:
Number of oxygen atoms = Number of moles of oxygen atoms x Avogadro's number Number of oxygen atoms = 0.1 moles x 6.022 x 10^23 atoms/mole Number of oxygen atoms ≈ 6.022 x 10^22 atoms
Therefore, there are approximately 6.022 x 10^22 oxygen atoms in 1.8 grams of water at STP.