How many ml of 1% solution do you need to prepare 200ml 4% solution using 7% and 1% stock solution?
Let x be the amount of 7% solution needed and y be the amount of 1% solution needed.
From the information given, we can set up the following equations:
x + y = 200 (eq. 1) (since the total volume of the solution is 200ml)
0.07x + 0.01y = 0.04(200) (eq. 2) (since the total % composition of the solution is 4%)
Simplifying eq. 2,
0.07x + 0.01y = 8 (eq. 3)
To solve the system of equations, we can multiply all terms of eq. 1 by 0.01
0.01x + 0.01y = 2 (eq. 4)
Now, subtract eq. 4 from eq. 3,
(0.07 - 0.01)x = 8 - 2
0.06x = 6
x = 100
Substituting x = 100 into eq. 1,
100 + y = 200
y = 200 - 100
y = 100
So, you need 100ml of the 1% solution and 100ml of the 7% solution to prepare a 200ml 4% solution using 7% and 1% stock solutions.