Question

How much of the 8% solution should we use to make 100g of a 3% solution?

Answer 1

Suppose x grams of 8% solution should be mixed to make 100 g of 3% solution.
here we shall have:
the amount of 3% solution in the 100 g will be:
3/100*100=3 grams
the the equation will be, 8% of what quantity becomes 3g?
(8/100)*x=3
hence solving for x we shall have:
0.08x=3
x=3/0.08
x= 37.8 grams
The implication of this is that, when you have 37.5 grams of 8% solution, that will contain 3  of pure chemical and hence when you add more solvent on top of 37.5 g until you reach 100g, that will be 3% solution.

Answer 2

Answer: 37.5 gram

Step-by-step explanation:

Since, by the dilution equation,

$M_1\times V_1 = M_2\times V_2$

Where, $M_1$ and $V_1$ are the molarity and volume of the concentrated stock solution and $M_2$ and $V_2$ are the molarity and volume of the diluted solution we want to make.

Here, $M_1 = 8\% = 0.08$,

$M_2 = 3\% = 0.03$,

$V_2 = 100\text{ gram}$

And, $V_1 = ?$,

$0.08\times V_1 = 100\times 0.03$

$0.08\times V_1 = 3$

$8\times V_1 = 300$

$V_1 = 37.5\text{ gram}$