Final answer:
To make 50 mL of an 18% HCl solution, 20 mL of a 15% HCl solution should be mixed with 30 mL of a 20% HCl solution.
Step-by-step explanation:
To determine the amount of a 15% HCl solution that must be mixed with a 20% HCl solution to obtain 50 mL of an 18% HCl solution, we need to set up a mixture equation. This type of problem is often solved by using the concept of concentration percentages and the conservation of mass principle.
Let the volume of the 15% solution be x mL. Then the volume of the 20% solution to mix with it would be (50 - x) mL since the total volume should add up to 50 mL. We can write the equation for the total amount of HCl from both solutions as follows:
0.15x + 0.20(50 - x) = 0.18 × 50
This can be simplified and solved for x:
- 0.15x + 10 - 0.20x = 9
- -0.05x = -1
- x = 20 mL
So, we need 20 mL of 15% HCl solution and (50 - 20) mL = 30 mL of 20% HCl solution to get the desired 18% solution.