Question

When 25 gm of $$N{a_2}S{O_4}$$ is dissolved in $${10^3}kg$$ of solution, its concentration will be…..
(A) 2.5 ppm
(B) 25 ppm
(C) 250 ppm
(D) 100 ppm

Answer 1

Hint: “ppm” stands for parts per million. We can easily find the ppm concentration of any solute in the solution if we know how much mass of solute is dissolved and what the mass of the solution is.

Complete answer:
Here, we will have to calculate the concentration in terms of ppm. Let’s see the formula to calculate ppm.
$$ppm = \dfrac{{{\text{Mass of solute(gm)}} \times {{10}^{ - 6}}}}{{{\text{Mass of solution(gm)}}}}$$
We are given in the question that,
Mass of solute ($$N{a_2}S{O_4}$$) = 25 gm
Mass of Solution = $${10^3}kg$$ = $${10^6}gm$$ (as $$1kg = 1000gm$$ )
Let’s put all the values in the formula of ppm,
$$ppm = \dfrac{{25 \times {{10}^6}}}{{{{10}^6}}}$$
$$ppm = 25$$
So, we have found that concentration of $$N{a_2}S{O_4}$$ in this solution is 25 ppm.
So, correct answer is (B) 25 ppm

Additional Information:
- ppm concentration is generally used for those solutes whose concentration is very dilute in the solution.
- In a simple way ppm concentration is defined as $$\mu g$$ of solute dissolved in 1 gm of solvent. That’s why we are multiplying the mass of solute by $${10^6}$$ because there, mass is taken in grams.
- As the density of water is $$1\dfrac{{gm}}{{ml}}$$ , if water is used as solvent and its volume is given, in that case we can also express mass of solution in grams which is same as volume of solution in ml.

Note: Whenever we put values in formulas like ppm, we need to be sure that we are putting values in proper units as the units in questions may be given differently than we may require to put in the formula. Always make a habit to write the unit of any value of property you have written if possible because that will minimize the errors.