SOLUTION: A flask contains 500 ml of an 80% alcohol solution in water. How much of this solution must be drawn off and replaced by water to obtain a solution having a concentration of 25% al
Algebra ->
Customizable Word Problem Solvers
-> Mixtures
-> SOLUTION: A flask contains 500 ml of an 80% alcohol solution in water. How much of this solution must be drawn off and replaced by water to obtain a solution having a concentration of 25% al
Log On
Question 1165827: A flask contains 500 ml of an 80% alcohol solution in water. How much of this solution must be drawn off and replaced by water to obtain a solution having a concentration of 25% alcohol? Answer by ikleyn(52786) (Show Source):
You can put this solution on YOUR website! .
A flask contains 500 ml of an 80% alcohol solution in water. How much of this solution must be drawn off and replaced by water
to obtain a solution having a concentration of 25% alcohol?
~~~~~~~~~~~~~~~~
Let V be the volume to drain off from 500 mL of the original mixture.
Step 1: Draining. After draining, you have 500-V mL of the 80% mixture.
Step 2: Replacing. Then you add V mL of water (the replacing step).
After the replacing, you have the same total liquid volume of 500 mL.
It contains 0.8*(500-V) of the pure alcohol.
So, your "concentration equation" is
= 0.25. (1)
The setup is done and completed.
Now you need to solve your basic equation (1). Multiply both sides by 500.
0.8*(500-V) = 0.25*500
0.8*500 - 0.8V = 125
400 - 125 = 0.8V
V = = 343.75 mL.
Answer. 343.75 mL of the original mixture should be drained and replaced with water.
