Final answer:
To find the concentration of the hydrochloric acid solution, we can use the equation of the titration reaction and the given information of the volume and concentration of sodium hydroxide. By calculating the moles of sodium hydroxide used and using the mole ratio, we can determine the moles of hydrochloric acid in the solution. Finally, by dividing the moles of hydrochloric acid by the volume of the solution, we can find the concentration of the hydrochloric acid solution.
Step-by-step explanation:
To determine the concentration of the hydrochloric acid solution, we can use the equation of the titration reaction HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l). From the given information, we know that 20.70 mL of 0.500 M NaOH was required to reach the end point when titrated against 15.00 mL of the HCl solution. The mole ratio between NaOH and HCl in the balanced equation is 1:1, which means that the moles of NaOH used is equal to the moles of HCl in the solution.
First, let's find the moles of NaOH used. Moles of NaOH = volume of NaOH (in L) × concentration of NaOH (in M) = (20.70 mL × 0.001 L/mL) × 0.500 M = 0.01035 mol.
Since the mole ratio is 1:1, the moles of HCl in the solution is also 0.01035 mol. Now we can calculate the concentration of the HCl solution. Concentration of HCl = moles of HCl / volume of HCl (in L) = 0.01035 mol / (15.00 mL × 0.001 L/mL) = 0.690 M.