a pharmacy adds 5ml of a stock solution into a 250 ml of water.
what is the percent v/v
my formula is used was
250/5=0.02
0.02x100=2%
is that a correct?
No, that is not correct. The calculation you did is finding the ratio of stock solution to water, not the percent v/v.
To find the percent v/v, you need to use the following formula:
(stock solution volume / total volume) x 100
In this case, the stock solution volume is 5 mL and the total volume is 250 mL + 5 mL = 255 mL.
(5 / 255) x 100 = 1.96%
So the percent v/v is approximately 1.96%.