Question

Calculate the amount of diluent required to make 100 mL of a 20% solution from a stock solution that is 80%.

Answer 1

Answer:

C. 75mL

Step-by-step explanation:

Let's find the solution.

Let's consider that the stock solution is XmL.

Also let's consider than the amount of diluent required is Y.

Because we need to add YmL to the stock solution to obtain a 100mL solution, then:

X+Y=100 which can be written as:

X=100-Y (eq. 1)

Now, the stock solution is 80% which means:

0.8=n/X where n is the solute, which can be written as:

n=0.8X (eq. 2)

Because we are trying to make a 100mL of a 20% solution then:

0.2=n/100, using eq. 2 we have:

0.2=(0.8X)/100, using eq. 1 we have:

0.2=0.8*(100-Y)/100

0.2*100/0.8=100-Y

25=100-Y

Y=100-25=75

In conclusion, we need to add 75mL, so the answer is C.