Calculate volume

Question

A technician is asked to prepare a dilution of a common laboratory disinfectant. The label indicates that a 1:39 dilution in water is required prior to use. Calculate the volume in mL of disinfectant required to make 2.0L. The answer must be in one decimal place

Answer 1

There is confusion about what 1:39 (or 1:10, 1:50, etc) actually means. Many take it to mean 1 part diluted to a final of 39 parts, while others take it to me a ratio of 1 part to 39 parts, i.e 1 part + 39 parts. I will answer this by assuming the first interpretation, i.e. 1 part diluted to 39 parts and since ml and liters are used, parts become mls (or liters).

So, we have the following:

2 L = 2000 mls

2000 / 39 = 51.3 mls

So, if you take 51.3 mls of the original solution, and dilute it to 2000 mls (2 L), this will represent a 1:39 dilution