NEED HELP ASAP

Question

You need 285 mL of a 5% alcohol solution. On hand, you have a 95% alcohol mixture. How much of the 95% alcohol mixture and pure water will you need to obtain the desired solution?

You will need

mL of pure water
and

mL of the 95% solution.

Answer 1

Hello Mike,

You can use the Alimentation method for mixtures:

     

               95%                0%(water)

                             5% (final)

 

                = 5-0             =95-5

                   5                    90

So  5 ml of 95% mixed with 90 ml of water will give you 95 ml of 5% mixture.

Now use simple proportion to determine how much of each you will need for a total of 285 ml.

Pradip

Answer 2

Alright, we are going to work with the volume of water.

 

a + b = 285

0.05a + b = 0.95(285)

 

b = 285 - a

 

b = 270.75 - 0.05a

 

Since b equals two different things, they equal each other.

 

285 - a = 270.75 - 0.05a

0.95a = 14.25

a = 15

 

b = 285 - 15

b = 270

 

We need 15 mL of the solution and 270 mL of pure water.