Question

Using the average atomic masses for each of the following elements calculate the mass in AMU of each of the following samples

Answer 1

Calculate the mass, in amu, of 278 atoms of Li.

1) We need to find Li (Lithium) in the periodic table.

1) The atomic mass of Lithium is 6.94 u.

`\text{The mass of Lithium sample=}\frac{6.94\text{ u of Lithium}}{1\text{ mole of Lithium}}\cdot\frac{1\text{ mole of Lithium}}{6.022\cdot10^(23)\text{ atoms of Lithium}}`

2) We can cancel some units and rearrange the equation.

`\text{Lithium sample = }\frac{6.94\text{ u of Lithium}}{6.022\cdot10^(23)\text{ atoms of Lithium}}`

3) Multiply the equation above by the number of atoms

`\text{Lithium Sample = }\frac{6.94\text{ u of Lithium}}{6.022\cdot10^(23)\text{ atoms of Lithium}}\cdot\frac{278\text{ atoms of Lithium}}{\square}\text{ = 3.20}\cdot10^(-21)\text{ u of Lithium}`

The mass of 278 atoms of Lithium is 3.20*10^-21 u