How many atoms are contained in a sample of krypton (Kr) that weighs 8.38g? ?

Question

Can someone please explain how to do this?

Answer 1

probably somewhere around 32-33

Answer 2

1)Detemine the number of moles of Kr first using the formula:

        moles = mass/Mr

                 = 8.38/83.8

                 = 0.1

2)Now:

      1 mole of Kr contains 6.02 *10^23 atoms of Kr

            1 mole Kr = 6.02* 10^23 atoms

           0.1 moles Kr = (6.02*10^23) * (0.1)

                              =  6.02 * 10^22 Kr atoms.

NB: You may be wondering why  1 mole of Kr has 6.02 * 10^23 atoms of Kr.But the definition of the mole says the amount of substance that contains the same number of stated elemantal particles (atoms,molecules,ions) as there are in 1 mole of carbon-12(which contains 6.02* 10623 atoms).Stated elemental particles are the particles the substance contains...Kr contains atoms.

Good Luck.

Answer 3

Moles Kr = mass / atomic mass = 8.38 g / 83.798 g/mol =0.100

1 mole => 6.02 x 10^23 ( Avogadro's number)

atoms  Kr= 0.100 x 6.02 x 10^23 =

= 6.02 x 10^22