2 Answers

C1V1 = C2V2
That is – concentration times volume is always a constant ratio.
So, (6.0 M)(25 ml) = (Final Concentration)(125 ml).
Solve for Final Concentration by dividing both sides by 125 ml and you get that the Final Concentration is 1.2 M.
Source(s): Personal Knowledge 
Figure out how many moles there are in the original solution (0.025L)*(6mol/L). The liters cancel out and you have moles. Divide the number of moles by 0.125L (the new volume of the solution) to find the molarity.