A25.0 ml sample of hno3 solution requires 35.7 ml of 0.108 m na2co3 to completely react with all of the hno3 in the solution. what is the concentration of the hno3 solution?

First, let write down the reaction equation

2HNO3 + Na2CO3 ---> H2CO3 + 2NaNO3

find the moles of Na2CO3 in the solutions

moles= M x L---> moles Na2CO3= 0.108 M x  0.0357 L = 0.00386 mole

then do mole-mole ratio

0.00386 mol Na2CO3 ( 2 mol HNO3/ 1 mol NaCO3)= 0.00771 mol HNO3

to find concentration (molarity= mol/ Liters)

M= 0.00771 moles/ 0.025 L= 0.308 M HNO3