Question

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

A. 0.0143
B. 0.054
C. 19
D. 230

I really need help with this problem. I did the math and got 18.4, and I can't round it. Would it be C?

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 =
`(given mass in g)/(molar mass)` (1)

Number of zinc atoms is equal to
`1.7*10^(23)`, by Avogadro number, number of moles can be calculated.

As, 1 mol=
`6.022*10^(23)` atoms, hence,

`1.7*10^(23)*(1 mol)/(6.022*10^(23) )`

= 0.2822 mol

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

0.2822 mol =
`(mass in g)/(65.4 g/mol)`

mass in g =
`{0.2822 mol * 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.