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) mol of $H_{2}O$ = $\frac{no. of molecule}{L}$
                            = $\frac{1000 molecules}{6.03 * 10^{23} molecules/mol }$
                            = 1.658  *   $10^{-21} mol$

18) mol = $\frac{molecule}{L}$
      $\frac{Mass}{Mr} = \frac{Molecule}{L}$
      Let mass of oxygen = x
      $\frac{x}{(2 * 1) + (16)} = \frac{6 * 10^{23} }{6.03 * 10^{23} }$
      $x = (6 * 10^{23} ) (18 g/ mol)$
             =  17.9 g