How many ml of 21% stock solutions do you need , if you need to prepare 360ml of 10% using 21% and 3% solutions?
Let's assume the amount of 21% stock solution needed is x ml.
We know that the total volume of the 10% solution to be prepared is 360 ml.
So, the amount of 3% solution needed would be (360 - x) ml.
We can create an equation based on the concentration of the solutions:
21%(x) + 3%(360 - x) = 10%(360)
Simplifying the equation:
0.21x + 0.03(360 - x) = 0.10(360)
0.21x + 10.8 - 0.03x = 36
0.18x = 36 - 10.8
0.18x = 25.2
x = 25.2 / 0.18
x ≈ 140
Therefore, you will need approximately 140 ml of the 21% stock solution.