You want to determine the molar heat of solution of sodium chloride using a 10.0 g sample of NaCl(aq) and 50.0 mL of water in a coffee cup calorimeter. Which of the following equations would you use? Assume the specific heat of the solution is the same as the specific heat of water.
A. q = (50.0 g)(4.18 J/g K)(Ti - Tf)
B. q = [(10.0 g)(4.18 J/g K)(Tf - Ti)]/[10.0 g/(58.44 g/mol)]
C. q = (60.0 g)(4.18 J/g K)(Tf - Ti)
D. q = (60.0 g)(4.18 J/g K)(Ti - Tf)
E. q = [(60.0 g)(4.18 J/g K)(Tf - Ti)]/[10.0 g/(58.44 g/mol)]
I wouldn't use any of them.
But one of these has to be the answer.
I guess the intent is to heat ALL of the solution with the same specific heat of water so I would go with E.
Ok. Thanks once again!
To determine the molar heat of solution of sodium chloride, we can use the equation:
q = (mass of solution) × (specific heat capacity of water) × (change in temperature)
In this case, the mass of the solution is the mass of water plus the mass of sodium chloride.
Looking at the options:
A. q = (50.0 g)(4.18 J/g K)(Ti - Tf)
This equation only accounts for the heat capacity of water and does not include the mass of sodium chloride, so it is not correct.
B. q = [(10.0 g)(4.18 J/g K)(Tf - Ti)]/[10.0 g/(58.44 g/mol)]
This equation includes the mass of sodium chloride and accounts for the heat capacity of water. It also divides by the molar mass of sodium chloride to get the molar heat of solution. This seems like the correct equation.
C. q = (60.0 g)(4.18 J/g K)(Tf - Ti)
This equation assumes the mass of the solution is 60.0 g, which is incorrect since we only have 50.0 mL of water and 10.0 g of sodium chloride.
D. q = (60.0 g)(4.18 J/g K)(Ti - Tf)
Similar to option C, this equation assumes the mass of the solution is 60.0 g, which is incorrect.
E. q = [(60.0 g)(4.18 J/g K)(Tf - Ti)]/[10.0 g/(58.44 g/mol)]
This equation includes the mass of sodium chloride and accounts for the heat capacity of water. However, it incorrectly divides by the molar mass of sodium chloride twice. So, it is not correct.
Therefore, the correct equation to use is option B:
q = [(10.0 g)(4.18 J/g K)(Tf - Ti)]/[10.0 g/(58.44 g/mol)]