1. Understand the Connection
* Molecules: The smallest unit of a compound that retains the chemical properties of that compound.
* Grams: A unit of mass.
The key to bridging the gap is the mole (mol).
* Avogadro's Number: One mole of any substance contains 6.022 x 10^23 particles (atoms, molecules, ions, etc.). This is a massive number, but it allows for convenient conversions.
2. Conversion Steps
1. Convert molecules to moles: Divide the number of molecules by Avogadro's number.
2. Calculate molar mass: Find the molar mass of the compound (the mass of one mole) by adding the atomic masses of all the atoms in the compound. You can find atomic masses on the periodic table.
3. Convert moles to grams: Multiply the number of moles by the molar mass.
Example: How many grams are in 1.5 x 10^24 molecules of water (H₂O)?
1. Molecules to Moles:
* 1.5 x 10^24 molecules / 6.022 x 10^23 molecules/mol = 2.49 mol
2. Molar Mass of Water:
* H: 1.01 g/mol (x2 for two hydrogen atoms) = 2.02 g/mol
* O: 16.00 g/mol
* Total Molar Mass (H₂O): 2.02 g/mol + 16.00 g/mol = 18.02 g/mol
3. Moles to Grams:
* 2.49 mol x 18.02 g/mol = 44.9 g
Therefore, 1.5 x 10^24 molecules of water weigh 44.9 grams.
Key Points:
* Units are crucial! Make sure to keep track of the units throughout the calculation to ensure you end up with grams.
* Periodic Table: Use the periodic table to find the atomic masses of elements.
* Calculator: Use a scientific calculator for large numbers.
Let me know if you'd like to try another example!
