Question

how many atoms are in 82.0 mL of water

Answer 1

You'd go about calculating this by using Avogadro's number, which links the number of atoms or molecules of a substance with the number of moles of that substance you have.

According to this relationship, every mole has 6.022⋅1023 atoms

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Since water is a molecule, 1 mole of water will always have 6.022⋅10^23 molecules of water.

One mole of water is 18.016 grams, so in 82 grams the number of moles is:

moles of water = 82 grams x (1 mole/18.016 grams)
moles of water = 4.54 moles

so 4.54 X 6.022 x 10^23

= 27.74 x 10^23 atoms present in 82 ml water.