# What mass of Cr(NO_3)_3*9H_2O is required to make a 100*mL volume of a solution that is 2.00xx10^-3*mol*L^-1 with respect to Cr^(3+)?

May 28, 2017

We need a mass of approx...$0.8 \cdot g$

#### Explanation:

We use the relationship, $\text{Concentration"="Moles of solute"/"Volume of solution}$,

and thus to get the $\text{moles of solute}$, we take the product............

$\text{Moles of solute"="Concentration"xx"Volume}$

$= 100.0 \cdot m L \times {10}^{-} 3 \cdot L \cdot m {L}^{-} 1 \times 0.0200 \cdot m o l \cdot {L}^{-} 1$

$= 2.000 \times {10}^{-} 3 \cdot m o l$.

And this represents a mass of...............

$= 2.000 \times {10}^{-} 3 \cdot m o l \times 400.15 \cdot g \cdot m o {l}^{-} 1 = 0.800 \cdot g$.

Note that this question has been poorly specified. When you say $\text{chromium nitrate nonahydrate}$ I have ASSUMED that you mean the $C r \left(+ I I I\right)$ hydrate, $C r {\left(N {O}_{3}\right)}_{3} \cdot 9 {H}_{2} O$, whose formula mass is $400.15 \cdot g \cdot m o {l}^{-} 1$.