# What is the "ppm" concentration of salt in a solution composed of 3.5*g of salt, and 96.5*g water?

Feb 10, 2018

So, in $100 \cdot g$ of solution there are $3.5 \cdot g$ of salt, and the balance water?

#### Explanation:

By definition...$\text{1 ppm} = \frac{1 \cdot m g}{1 \cdot L}$...and we call this ratio $\text{parts per million}$ because there are $1000 \times 1000 \cdot m g \equiv {10}^{6} \cdot m g$ IN ONE LITRE VOLUME of water.

...most of the time we can ignore the density because the mass of the solute is miniscule...here we assume that the $96.5 \cdot g$ of solvent water expresses a volume of $96.5 \cdot m L$ in the SOLUTION...

And so we take the quotient....

$\frac{3.5 \cdot g \times {10}^{3} \cdot m g \cdot {g}^{-} 1}{96.5 \cdot m L \times {10}^{-} 3 \cdot L \cdot m {L}^{-} 1} = 36 , 269 \cdot m g \cdot {L}^{-} 1 \equiv 36 , 269 \cdot \text{ppm}$.

Do you think this $\text{ppm}$ quotation of concentration is appropriate here?

Note that I have been asked by several posters whether this dissolution reaction of sodium chloride in water represents a physical or chemical reaction. My own very conservative notions of the definition of chemical reaction, INSISTS that such a process, while REVERSIBLE, is CHEMICAL. Chemical change is characterized by the formation of new substances and the making and breaking of chemical bonds. The dissolution reaction certainly qualifies...

$N a C l \left(s\right) \stackrel{{H}_{2} O}{\rightarrow} N {a}^{+} + C {l}^{-}$

Where the ion is the aquated complex, i.e. $N {a}^{+} \equiv {\left[N a {\left(O {H}_{2}\right)}_{6}\right]}^{+}$..