Harrison W. answered 04/16/20
Yale grad, 100th percentile MCAT, applying to med school
Hey Duch! Thanks for your question.
Here, it's probably easiest to use the equation C1*V1 = C2*V2, where "C" stands for concentration and "V" stands for volume. You can rearrange the equation to read: V1 = (C2*V2)/C1
If you want a final solution of 100mL and a concentration of 0.35M, plug those values in to the numerator on the right side of the equation. You know your initial concentration (C1) is 0.75M, so you can plug that in too. From there, its just a simple calculation:
V1 = (0.35M * 100mL) / 0.75M
V1 = 46.67mL
So in your final solution, you'll need 46.67mL of stock KCl, and the rest (53.33mL) will be water.
Hope this helps!!