word problem of finding solutions

Question

keith robinson is a chemistry teacher who needs 1 liter of a solution of 5% hydrochloric acid to carry out an experiment. if he only has a stock solution of 99% hydrochloric acid how much water and how much stock solution of HCL must he mix to get 1 liter of 5% solution/

Answer 1

1 Liter = 1000 ml.  To answer the question set up a ratio:  Use X to be the amount of stock needed.  

 

X/99 = 1000/5, then solve for X:

 

5x= 99, divide both sides by 5 and X = 19.8 ml of the 99% stock plus (1000 - 19.8 = 980.2) 980.2 ml of water to make 1 liter of 5% HCl.

 

Hope this helps!  Best wishes.