help me please

Question

A pharmacist wants to add water to a solution that contains 80% medicine. She wants to obtain 12 oz. of a solution that is 20% medicine. How much water and how much of the 80% solution should she use

Answer 1

Hello Teo

 

The above process is called dilution where water is added to a solution of a high concentration in order to decrease the concentration.  The equation that you can use is:

 

C_iV_i = C_fV_f

 

Where C is the concentration, V is the volume, and the subscripts i and f refer to the initial and final amounts.

 

80% V_i = 20% x 12 oz

 

V_i = (20% x 12 oz) / 80% = 3 oz

 

Amount of water to be added = 12 - 3 = 9 oz.

 

Take 3 oz of the 80% solution and add 9 oz of water to give 12 oz of the 20% solution.