# Question #d2535

Aug 17, 2017

$1 m o l {L}^{-} 1$

#### Explanation:

Firstly recall that;

$1000 m l = 1 L$

$\left(N a = 23 , \textcolor{w h i t e}{x} O = 16 , \textcolor{w h i t e}{x} S = 32\right)$

$M o l a r i t y = \text{Moles of solute"/"Volume of Solvent or Solution}$

$\text{Moles of solute" = "Mass of solute"/"Molar mass of solute}$

$\text{Volume of solvent} = 1000 m l = 1 L$

$\text{Solute} = N {a}_{2} S {O}_{4}$

$\text{Mass of solute} = 142 g$

$\text{Molar mass of solute} = \left(23 \times 2\right) + 32 + \left(16 \times 4\right) g m o {l}^{-} 1$

$\textcolor{w h i t e}{X X X X X X X X X X} = 46 + 32 + 64 g m o {l}^{-} 1$

$\textcolor{w h i t e}{X X X X X X X X X X} = 142 g m o {l}^{-} 1$

$\Rightarrow \text{Moles of solute} = \frac{142 \cancel{g}}{142 \cancel{g} m o {l}^{-} 1}$

$\Rightarrow \text{Moles of solute} = 1 m o l$

$\Rightarrow M o l a r i t y = \text{Moles of solute"/"Volume of Solvent or Solution}$

$\Rightarrow M o l a r i t y = \frac{1 m o l}{1 L}$

$\Rightarrow M o l a r i t y = 1 m o l {L}^{-} 1$