0.1M solution of HCl is added to 0.180M solution of NaOH. (each 25ml) Concentration of OH-(aq) remaining in the solution, is 0.04M. explain please  

Expert Answers
ndnordic eNotes educator| Certified Educator

Start by finding the number of moles of each reactant you are using.

For HCl you have 0.0025 moles

For NaOH you have 0.0045 moles.

In the neutralization reaction all of the HCl will react with 0.0025 moles of NaOH, leaving 0.0020 moles of NaOH.  But that remaining NaOH is now in 50 mL of solution, not the original 25 ml you started with.

0.002 moles of NaOH in 50 ml is equivalent to a 0.04 M solution of NaOH.