In a titration, a few drops of an indicator are added to a flask containing 35.0 milliiters of HNO3(aq) of unknown concentration. After 30.0 millliters of 0.15 M NaOH(aq) solution is slowly added o the flask, the indicator changes color, showing the acid is neutralized. Which choice is a correct numerical setup for calculating the concentration of the HNO3(aq) solution

0.13M HNO3 is the concentration of the unknown

Explanation:

Nitric acid, HNO3, reacts with NaOH as follows:

HNO3 + NaOH  → H2O + NaNO3

Where 1mol HNO3 reacts with 1mol NaOH

To find the concentration of HNO3 we must find, as first, the moles NaOH added = Moles HNO3 in the solution:

30mL * (1L / 1000mL) * (0.15mol / 1L) = 0.0045 moles HNO3

In 35.0mL = 0.035L:

0.0045 moles HNO3 / 0.035L =

0.13M HNO3 is the concentration of the unknown