Question

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

Answer 1

So, in `100*g` of solution there are `3.5*g` of salt, and the balance water?

Explanation:

By definition...`"1 ppm"=(1*mg)/(1*L)`...and we call this ratio `"parts per million"` because there are `1000xx1000*mg-=10^6*mg` 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*g` of solvent water expresses a volume of `96.5*mL` in the SOLUTION...

And so we take the quotient....

`(3.5*gxx10^3*mg*g^-1)/(96.5*mLxx10^-3*L*mL^-1)=36,269*mg*L^-1-=36,269*"ppm"`.

Do you think this `"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...

`NaCl(s) stackrel(H_2O)rarrNa^+ + Cl^-`

Where the ion is the aquated complex, i.e. `Na^+ -=[Na(OH_2)_6]^+`..