Question

17. How many moles are there in a sample containing 1000 molecules of H2O?18. If you wanted a sample of H2O containing 6 x 23molecules, how could you measapproximate number without counting?

Answer 1

17.For a sample of 1000 molecules of H₂O, the number of moles is approximately
`\(1.66 * 10^(-21)\)` moles.
18.To obtain a sample with
`\(6 * 10^(23)` molecules without counting, measure out approximately 18 grams of water, as the molar mass of water is 18 grams/mol.

17. Number of Moles in a Sample with 1000 Molecules of H₂O:

To find the number of moles in a sample with 1000 molecules of H₂O, we can use Avogadro's number, which is approximately
`\(6.022 * 10^(23)\)` entities per mole. The formula to calculate moles is:

`\[ \text{Number of moles} = \frac{\text{Number of molecules}}{\text{Avogadro's number}} \]`

Substituting the given values:

`\[ \text{Number of moles} = (1000)/(6.022 * 10^(23)) \]`

Calculating this yields the number of moles in the given sample.

`\[ \text{Number of moles} \approx 1.66 * 10^(-21) \, \text{moles} \]`

18. Measuring a Sample with
`\(6 * 10^(23)\)` Molecules Without Counting:

To obtain a sample of H₂O with
`\(6 * 10^(23)\)` molecules without counting each one, one can use the molar mass of water. The molar mass of water is approximately 18 grams/mol. Since one mole contains Avogadro's number of molecules, 18 grams of water will contain
`6 * 10^(23)\)` molecules. Therefore, measuring out about 18 grams of water provides a sample with the desired number of molecules.

Answer 2

17) mol of
`H_(2)O` =
`(no. of molecule)/(L)`
=
`(1000 molecules)/(6.03 * 10^(23) molecules/mol )`
= 1.658 *
`10^(-21) mol`

18) mol =
`(molecule)/(L)`

`(Mass)/(Mr) = (Molecule)/(L)`
Let mass of oxygen = x

`(x)/((2 * 1) + (16)) = (6 * 10^(23) )/(6.03 * 10^(23) )`

`x = (6 * 10^(23) ) (18 g/ mol)`
= 17.9 g