Final answer:
To obtain a 50% solution of HCl, one must add 10 cc of pure hydrochloric acid to 20 cc of the 30% hydrochloric acid solution.option d.
Step-by-step explanation:
The student's question is about preparing a mixture of hydrochloric acid to achieve a certain concentration. To find out how many cubic centimeters of pure hydrochloric acid should be added to 20 cubic centimeters (cc) of a 30% solution to obtain a 50% solution, we can set up an equation based on the concept of mass balance. The mass of hydrochloric acid in the original solution plus the mass of pure hydrochloric acid added will equal the mass of hydrochloric acid in the final solution.
Let x be the volume of pure hydrochloric acid in cc added. The initial amount of HCl is 30% of 20 cc, which is 0.30 x 20 = 6 cc of HCl. The final solution volume will be 20 cc + x, and we want this to be a 50% HCl solution.
So the equation will be setup as follows:
0.30 x 20 + x = 0.50 x (20 + x)
When we solve for x, we find that x is equal to 10 cc. Therefore, 10 cc of pure HCl should be added to the original solution to achieve the final concentration of 50%.