The question's in the detailed location because i didn't have enough room here.?

Question

20.00 mL of 1.364-M HNO3 solution and 100.00 mL of 0.102-M HNO3 solution are combined and then diluted with water until the total volume is 250.00 mL.
What is the molarity of this HNO3 solution?

Answer 1

This is just book-keeping but the poor old chemistry teacher seems to be stuck with it. All it is, is keeping track of amount of stuff, in this case of HNO3.

Use Amount (millimoles) = conc (molarity, M) x volume (mL)

to find number of millimoles in each of the two HNO3 solutions. Add them up. Then use the same equation in reverse (divide total millimoles by total final volume in mL) to get your final answer.