10.618 g of an unknown salt is dissolved in a coffee cup calorimeter that contains 50.0 mL of water. The measured temperature decreased from 23.8 °C to 22.7 °C. Identify the unknown salt. The specific heat of water is 4.184 J g^-1 °C^-1, and assume the density of the solution is 1.00 g mL^-1.

Question

Quizplus · Accepted Answer

First, calculate the amount of heat absorbed by the solution:
q = mCΔT = (10.618 g)(4.184 J g-1 °C-1)(23.8-22.7) °C = 49.68 J
Next, convert J to kJ and use it to calculate the enthalpy change per mole of the unknown salt:
ΔH = -q/n = -49.68 J / (10.618 g / 41.99 g/mol) = -0.91 kJ/mol
Comparing this value to the given enthalpies of formation, we can see that it matches that of NaF. Therefore, the unknown salt is NaF.

10618 G of an Unknown Salt Is Dissolved in a Coffee