Question

Hello, I need help answering these two questions. Thank you!

1. How do I make 5 mL of a 1/10 dilution of a solution?

2. How do I figure out the concentration of an undiluted solution(I have the absorbance but the reading is off) if I am unable to use a standard curve?

Answer 1

Q 1. 1:10 dilution means 1 part (or mL) of original solution and 9 part (or mL) of diluent in total volume (final volume) of 10 mL. In condition when you need 5 mL as final volume one need to multiply dilution with final volume. for instance;

i.e 0.5 mL of original solution and make up the volume to 5 mL by adding 4.5 mL of diluent.

Q 2. There are two ways to know the concentration of unknown sample:

i. direct extrapolation from standard graph and

ii. deriving the correlation between optical density (absorbance) and concentration using linear region of standard graph.

both these methods follow some rules;

a. Standard graph should have linear region in certain concentration range.

b. The absorbance of unknown should fall in the range of standard graph. Range is nothing but the linear region of graph which gives you exponential increase in absorbance with increase in concentration. If the absorbance of unknown is greater than the range, then dilution of the unknown sample is required and if the absorbance is lesser than the range then sample volume has to be increased. To overcome this issue, it is always suggested to assay various aliquots of unknown samples.