Question

How many atoms are in 22.5g of pentane

Answer 1

mass of pentane = 22.5g

molar mass of pentane(C5H12) = 5 x 12.01 + 12 x 1.008

                                                     = 60.05 + 12.096

                                                     = 72.146g/mol

                                                     = 72.15g/mol

22.5g pentane x 1 mol pentane  x  6.022 x 10^23 molecules ofpentane

                            72.15g pentane             1 mol pentane

= 22.5 x 6.022 x 10^23

            72.15

= 1.88 x 10^23 pentane molecules

1 pentane molecule has 5 C + 12 H atoms = 5+12 = 17 atoms

Hence;

1.88 x 10^23 pentane molecules x    17 atoms                      

                                                              1 pentane molecule

= 31.925 x 10^23 atoms

=   3.2 x 10^22 atoms are present in 22.5g of pentane.

3.2 x 10^22 atoms