Question

A 4.17 g sample of a pure element contains 3.35 x 10^22 atoms. What is the element?​

Answer 1

Answer : The element is, Arsenic (As)

Solution : Given,

Mass of a pure element = 4.17 g

Number of atoms = $3.35\times 10^{22}$

First we have to calculate the moles of a pure element.

$\text{Number of moles of an element}=\frac{\text{Given atoms of an element}}{\text{Avogadro's number}}=\frac{3.35\times 10^{22}}{6.022\times 10^{23}}=0.0556moles$

Now we have to calculate the molar mass of an element.

Formula used :

$\text{Moles of an element}=\frac{\text{Mass of an element}}{\text{Molar mass of an element}}$

Now put all the given values in this formula, we get

$0.0556mole=\frac{4.17g}{\text{Molar mass of an element}}$

$\text{Molar mass of an element}=75g/mole$

Thus, the arsenic is the element which has molar mass 75 g/mole.

Hence, the element is, Arsenic (As)