Question

How many moles of NaF are in 34.2 grams of a 45.5% by mass NaF solution?

Answer 1

"45.5% by mass NaF solution" means that 45.5% of the mass of the solution is NaF.

The solution has 34.2g of mass, so 45.5% of this is the mass of NaF:

$_{}m_{NaF}=34.2g\cdot0.455=15.561g$

To transform this into moles, we need the molar mass of NaF, which we can calculate using the atomic masses of Na and F:

$M_{NaF}=M_{Na}+M_F\approx22.9897g/mol+18.9984g/mol=41.9881g/mol$

So, the number of moles is:

$M_{NaF}=\frac{m_{NaF}}{n_{NaF}}=\frac{15.561g}{41.9881g/mol}\approx0.371mol$

So, there are approximately 0.371 mol of NaF.