Question

1)

Rank the elements in the table below in order from least to greatest number of atoms.

Mass (g)	Element
11.1	He
16.4	Be
33.6	Mg
88.9	Ca

Note: Enter the symbol for the elements in the ranking.

(least)  <  <  <  (greatest)

2)

An ionic compound   is prepared according to the following unbalanced chemical equation.

A 0.133-g sample of   contains   molecules. The compound   consists of 79.76%   by mass.

a

What are the identities of   and  ?

=

=

3)

An ionic compound   is prepared according to the following unbalanced chemical equation.

A 0.133-g sample of   contains   molecules. The compound   consists of 79.76%   by mass.

a	What are the identities of   and  ? = =

Answer 1

1)

mass of He = 11.1 g

moles of He = 11.1 / 4 = 2.775

number of atoms = 2.775 x 6.023 x 10^23

                            = 1.67 x 10^24 atoms

moles of Be = 16.4 / 9.012 = 1.8197

number of atoms = 1.10 x 10^24 atoms

moles of Mg = 33.6 / 24 = 1.4

number of atoms = 8.43 x 10^23

moles of Ca = 2.22

number of atoms = 1.34 x 10^24 atoms.

least ---------   greatest.

Mg < Be   < Ca   <   He .