This problem seems simple enough, yet my professor says my answer is incorrect. Here is the problem. 1 ml of a 0.10 M solution of HCL is added to 21 ml of distilled water. What is the final concentration of the solution (M)? Im going to use the equation C1*V1=C2*V2 Where C1 is the initial concentration (M) and C2 is the final Concentration, and V1 is initial Volume, and V2 is final volume If I add 1ml of HCl to 21ml of H2O, I will have 22ml of solution. This is V2, therefore C1V1/V2=C2 (0.1M)(1ml)/(22ml)=C2 C2= 0.0045 M What am I overlooking? Thanks in advance.