Question

in HNO3 titration, you add few drops of phenolphthalein indicator to 50.0 mL of acid in a flask. you quickly add 20.00 mL of 0.0547 M NaOH but overshoot the end point, and the solutions turn deep pink. instead of starting over, you add 30.00 mL of acid, and the solution turns colourless. then, it takes 7.05 mL of NaOH to reach the end point. what is the concentration of the HNO3 solution?

Answer 1

mols base = mols acid
M x L base = M x L acid
M x (add all the L base) = M x L (add on the L acid)
The only unknown is M acid.