The student determined the enthalpy of neutralization to be equal to -33.5 kJ/mol by mixing 100.0 mL 2.00 M HCl and 100.0 mL 2.00 M NaOH solutions. The temperature increased by 6.0oC. The student suspected that the solutions prepared were wrong and titrated the NaOH solution. It turned out the be that the concentration of NaOH was indeed 1.70 M. What was the concentration of HCl solution used?