Question

The mole is a counting number that allows scientists to describe how individual molecules and atoms
react. If one mole of atoms or molecules is equal to 6.022 × 1023 atoms or molecules, how many molecules
are in a 23.45 g sample of copper (II) hydroxide, Cu(OH)2? Express your answer to the correct number of
significant figures. (MM of Cu(OH)2 is 97.562 g/mol). Be sure to show all steps completed to arrive at the
answer.

Answer 1

We know all required information for calculation the number of molecules:

$m(Cu(OH)_2)=23.45~g$

$MM(Cu(OH)_2)=97.562~g/mol$

$Na=6.022×10^{23}~mol^{-1}$

First we must find the number of moles:

$n=\frac{m(CuOH)_2}{MM(Cu(OH)_2}=\frac{23.45}{97.562}=0.240~mol$

Now we can calculate the number of molecules in 0.240 mol by the formula:

$N=n×Na=0.240×6.022×10^{23}=1.445×10^{23}$

So, the answer is $1.445×10^{23}$