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

We can use the equation q = mCΔT, where q is the heat absorbed or released, m is the mass of the solution, C is the specific heat of the solution, and ΔT is the change in temperature. Since the temperature decreased, we know that the reaction absorbed heat, which means that ΔH is positive. Therefore, we want to choose the salt with a positive enthalpy of dissolution.

First, we need to determine the mass of the solution. We know that the density of the solution is 1.00 g/mL, so the mass of the solution is 50.0 g. We need to subtract the mass of the salt from this value to get the mass of the water: 50.0 g - 10.618 g = 39.382 g.

Now we can calculate q:
q = (39.382 g + 10.618 g) x 4.184 J/g°C x (22.7°C -23.8°C)
q = -481.09 J

Note that the temperature change is negative because the temperature decreased. Also, we converted mL to g using the density of the solution.

Since q is negative, we want to choose the salt with a positive ΔH. Looking at the choices, the only salt with a positive ΔH is NaF with a value of 0.91 kJ/mol. Therefore, the best choice is A, NaF.

10618 G of an Unknown Salt Is Dissolved in a Coffee