A standard solution contained 0.8 mg/mL. A student took 2mL of the standard solution and added 10mL of water. What is the new/final concentration?

Question

I am taking BIOCH 265ZA: Introduction to Organic and Biochemistry. I took Chemistry approximately 8 years ago and I am just lost. Could you please explain the solution in basic terms. I would really appreciate your help. Thank you!

Answer 1

0.8 mg/ml x 2 ml = 1.6 mg in the 2 ml

Total volume of final soln is 2 ml + 10 ml = 12 ml

Final concentration = 1.6 mg/12 ml = 0.133 mg/ml = 0.1 mg/ml (to 1 significant figure). 

Answer 2

It says that each ml of the solution has 0.8 mg of contaminant ( whatever it is). So, if you take 2 ml it means the solution had 1.6 mg of the contaminant!!! Adding 10 ml pure water makes it 12 ml, so the final concentration is 1.6/12 or 0.4/3 or 0.133 mg/ml!

hope it helps for now ;)