Question

What is the mass in grams of  1.10 x 10^24 atoms of lithium?

......grams

How many lithium atoms are there in 11.2 grams of lithium?

......atoms

Answer 1

(i)

Number of moles of Li atom$=\dfrac{1.10\times 10^{24}}{6.022\times 10^{23}}=1.826mol$

Mass of Lithium=$\text{ no. of moles }\times \text{molar mass}=1.826\times 6.941=12.67g$

(ii)

Given, Mass of Lithim=11.2g

Moles of Lithium in $11.2g=\dfrac{11.2}{6.941}=1.6136$

Number of atoms $=\text{Number of moles }\times \text{Avagadro number}$

$=1.6136\times 6.022\times 10^{23}=9.717\times 10^{23} \text{atoms}$