Question

What is the concentration of solution in ppm when $5.0\,\times\;{10^{ - 5}}\;gm\;C{O_{2\;}}$is dissolved in $100\;ml\;$ Solution.
(A) $5$
(B) $500$
(C) $0.5$
(D) $5.0{\rm{ }}\times{\rm{ }}{10^{ - 5}}$

Answer 1

In the given question, the concentration of the solution we have to find in ppm. The full-form of ppm is parts per million, the amount of solute dissolved in the solvent is in very less quantity (one millionth). The concentration of the solution is measured in terms of molarity, normality, molality and ppm.

Complete step by step solution
The formula that we need to use to solve this question is as follows:
$ppm = \dfrac{{mass\;of\;solute}}{{mass\;of\;solution}} \times {10^6}$
One gram of solute in one million grams of solution, and solution is made up of solvent and solvent. Here, the most important is to write the data in the correct form so you do not get confused with the word solvent and solution. Here the concentration of solvent will be in a very large amount than that of solute.
Mass of the solute: $5.0\,\times\;{10^{ - 5}}\;gm\;C{O_{2\;}}$ and Mass of solution: $100\;ml\;$
These are given in the question, put all the values in the equation of ppm

$$ppm\;\; = \;\;\dfrac{{mass\;of\;solute}}{{mass\;of\;solution}} \times {10^6}\\\ ppm\;\; = \;\;\dfrac{{5.0\,\times\;{{10}^{ - 5}}\;gm\;C{O_{2\;}}}}{{100\;ml}} \times {10^6}\\\ ppm\;\; = \;\;0.5$$

**Hence, the correct answer is (C) $0.5$

Note: **
Here you should take care that in formula the value of the mass of solute needs to be substituted and not the value of the solvent. If the value is given in terms of mass of solvent then add the value of solute in that and then substitute it in the ppm formula.
The formula will become as given below:
$ppm\;\; = \;\;\dfrac{{mass\;of\;solute}}{{mass\;of\;solute\; + mass\,of\,\;solvent}} \times {10^6}$
While solving numerical do take care of the calculations.