# How do you measure concentration of a solution?

Jul 3, 2018

With difficulty. We want the quotient...

$\text{Concentration"="Amount of stuff"/"Amount of solution}$

#### Explanation:

There are various forms of the concentration expression,

$\text{mass of stuff"/"volume of solution}$, $\text{mass of stuff"/"mass of solution}$. Most commonly used is $\text{molarity"="moles of stuff"/"volume of solution}$...and units of $m o l \cdot {L}^{-} 1$ result. Weaker concentrations CAN be quoted in terms of $\text{parts per million}$..."1 ppm"-=1*mg*L^-1("of AQUEOUS solution")..

The product, $\text{volume (L)} \times m o l \cdot {L}^{-} 1$ gives an answer in $m o l$..

Unless, you are given the composition of the solution, i.e. $10 \cdot g$ of $H C l$ is dissolved in enuff water to give $1 \cdot L$ of solution, you are usually quoted solution concentration. In these circumstances we would take....

$\frac{\frac{10 \cdot g}{36.46 \cdot g \cdot m o {l}^{-} 1}}{1 \cdot L} = 0.274 \cdot m o l \cdot {L}^{-} 1$...WITH RESPECT to $H C l$...of course the acid speciates in solution..to give $\left[{H}_{3} {O}^{+}\right] = \left[C {l}^{-}\right] = 0.274 \cdot m o l \cdot {L}^{-} 1$..