Saline, which is used in medicine, is a 0.9% sodium chloride solution. How many grams of water should be added to 100 g of 12% sodium chloride solution to obtain a physiological solution.
Let’s find the mass of salt and water in the original solution.
The mass of the solution is 100 grams;
To find the mass of salt, it is necessary to multiply its mass fraction by the mass of the solution.
m salt = 100 x 0.12 = 12 grams;
To find the mass of water, subtract the mass of salt from the mass of the solution:
m water = 100 – 12 = 88 grams;
Check: 12 + 88 = 100;
In the new solution, 12 grams of salt will have a mass fraction of 0.9%.
Find the mass of this solution by dividing the mass of water by its new mass fraction
m solution 2 = 12 / 0.9 x 100 = 1,333.33 grams;
To obtain such a solution, the following mass of water must be added to the original solution:
m water 2 = 1 333.33 – 100 = 1 233.33 grams:
Checking: (88 + 1 233.33) / 0.991 = 1333.33;