Question

What is the mass of 1.7 × 1023 atoms of zinc (Zn)?

Answer 1

Number of moles is defined as the ratio of given mass in g to the molar mass.

The mathematical formula is:

Number of moles = $\frac{given mass in g}{molar mass}$   (1)

Number of zinc atoms is equal to $1.7\times10^{23}$, by Avogadro number, number of moles can be calculated.

As, 1 mol=$6.022\times10^{23}$ atoms, hence,

$1.7\times10^{23}\times\frac{1 mol}{6.022\times10^{23} }$

= 0.2822 mol

Now, from formula (1), calculate mass in g (molar mass of zinc = 65.4 g/mol)

0.2822 mol = $\frac{mass in g}{65.4 g/mol}$

mass in g  = ${0.2822 mol \times 65.4 g/mol$

= 18.45588 g

Thus, by rounding off the above number, it will come near about 19 g approximately.

Hence, option (C) is the correct answer.