need to make 5% solution from existing solutions of 10% and 2%?

Question

the awnser i have but how to work it is the problem
i know that i would need more 2% then 10% solution.

it deals with ( ml ) and its used in the pharmacy test

I know the awnser is 3ml of 10% and 5ml of 2% but I would like to know what kind of formula is need to solve this equation

Answer 1

at a basic level its just finding an average... but its a bit more complicated than that. just work it out on paper.

1 part 10% plus 1 part 2% equals 2 parts 6%.
1 part 10% plus 2 parts 2% equals 4.6%.

Just keep trying until it works

I think. Its been a while!

Answer 2

This can be worked out with a pair of linear equations. Let's assume a 100 mL final volume for the sake of convenience. Let A be the volume of the 10% solution and B be the volume of the 2% solution. Then we can write the following:

A + B = 100

For the solute, its components are 0.10*A and 0.02*B, yielding 5% of the 100 mL solution, or 5 mL. Thus:

0.10A + 0.02B = 5 => A + 0.20B = 50 (after multiplying by ten)

Subtracting the second equation from the first:

0.80B = 50 => B = 62.5 and thus A = 37.5

To make a 5% solution, you use 37.5% of the 10% solution and 62.5% of the 2% solution.

Hope that helps.

Answer 3

3 ml of 10% soln : 5 ml of 2% soln

Answer 4

use the formula N1V1=N2V2

Answer 5

try using heat