90 s. Time constant (15 s) × six = response time. Refer to Sect. 1.
The enthalpy change, ΔrH, for the first reaction is (2.0 J/0.038 mmole) = −52 J/mmole or −52 kJ/mole. ΔrH for the second reaction is 0 kJ/mole. ΔrH for dilution of the titrant is (−0.1 J/0.021 mmole) = +4.8 kJ/mole. Amines are usually more basic than carboxylates, so the expectation is that the amine is the first reaction, but the proof is the ΔrH value, −50 kJ/mole is a defining characteristic for protonation of amines, and 0 kJ/mole is a defining characteristic of protonation of carboxylate groups. The mole ratio of amine to carboxylate is (0.038/0.041) = 0.93. Refer to Sect. 3.9.
The stoichiometry is three stronger binding sites and four weaker binding sites. Both kinds of sites are cooperative, i.e., K1 ≈ K2 ≈ K3 < K4 ≈ K5 ≈ K6 ≈ K7. The enthalpy change, ΔrH, for the strong binding site is −50 kJ/mole and for the weaker binding site, −30 kJ/mole. The rounded endpoints show that the binding constants β3 and β4–7 could be calculated from these data. Refer to Sects. 2, 3.4, 3.8, and 5.
The concentration of nitrite is 59 μM. (11.21 J/°C)(0.0053 °C) = 0.0594 J; (0.0594 J)/(−402,000 J/mol)) = 0.1478 μmols product; 1:1 relationship, so the concentration is (0.1478)/(2.5 mL) = 59 μM. There is a large excess of sulfamic acid, i.e., (0.05 M)(106 μmole/mole)(10−3 L/mL)(0.15 mL) = 7.5 μmoles. The temperature measurement limits the answer to two significant digits. Refer to Sect. 3.3.
One H+ released. The reactions are