Answer
Mass percentage of Na in amalgam is 16.2 %.
Work Step by Step
The strategy: 1- find the mass of Na that produce 0.108 g $H_{2}$
2- Find mass percentage of Na in the amalgam.
2 Na (s) + 2 $H_{2}O$ (l) ${\longrightarrow} $ 2 NaOh (aq) + $H_{2}$ (g)
Step 1: to find the mass of Na when we know the amount 0.108 g of $H_{2}$ :
g $H_{2}$ ${\rightarrow}$ mol $H_{2}$ ${\rightarrow}$ mol Na${\rightarrow}$ g Na
The conversion factors are:
$\frac{1 mol (H_{2})}{Molar mass (H_{2})}$ to convert to moles $H_{2}$, where Molar mass $H_{2}$:
Molar mass $H_{2}$= 2 x 1.008 g = 2.016 g
$\frac{2 mol (Na)}{1 mol (H_{2})}$, to convert the moles of $H_{2}$ to mol of Na.
$\frac{Molar mass(Na)}{1 mol(Na)}$ to convert to g of Na, where the molar mass of Na is:
Molar mass Na = 1 x 22.99 g = 22.99 g
Now we use the conversion factors to find the mas of Na:
0.108 g $H_{2}$ x $\frac{1 mol (H_{2})}{Molar mass (H_{2})}$ x$\frac{2 mol (Na)}{1 mol (H_{2})}$ x $\frac{Molar mass(Na)}{1 mol(Na)}$ =
0.108 g $H_{2}$ x $\frac{1 mol (H_{2})}{2.016g}$ x$\frac{2 mol (Na)}{1 mol (H_{2})}$ x $\frac{22.99g}{1 mol(Na)}$ = .
So the mass of Na is 2.463 g
Step 2 - Find the mass percentage of Na in amalgam.
mass percentage of Na = $\frac{mass _(Na)}{mass_(amalgam)}$ x 100%
mass percentage of Na = $\frac{2.463}{15.23}$ x 100%
mass percentage of =Na 16.17%, or mass percentage of Na in amalgam is 16.2 %.
