PRELAB QUESTIONS (RESPOND ON A SEPARATE SHEET OF PAPER): A student determined th

Question

PRELAB QUESTIONS (RESPOND ON A SEPARATE SHEET OF PAPER): A student determined the calorimeter constant, using the procedure described in this manual. The student added 50.00 mL of hot water to 50.00 mL of cold water in a Styrofoam cup. The initial temperature of the cold water was 21.00 °C and that of the warm water 29.15 °C·The maximum termperature of the mixture was found to be 24.81 (by graphing and extrapolating the data). Assume the density of water is 1.00 g mL and the specific heat of water is 4.184 J g K1. Calculate the calorimeter constant, Col Consider the possibility of substituting a glass beaker for the Styrofoam cups when performing this experiment. Would you expect the calorimeter constant of the Styrofoam cups to be larger, smaller, or the same as that of the beaker? Briefly explain (hint: the calorimeter constant represents the heat capacity of the calorimeter; that is, the amount of heat in joules required to raise its temperature by 1 degree). 2. Write balanced chemical equations for the neutralization reactions used in this experiment. Identify the limiting reagent for each reaction (briefly explain your answers). Why is the concentration of H3PO4 solution 0.67 M and that of HCl 2.00 M? 3. Calculate the theoretical standard molar enthalpies for the neutralization reactions using the standard molar enthalpies of formation (write net ionic equations first, then search for standard molar enthalpies of formation in thermodynamic data tables) 4. Be sure to get the report from the course website and complete all sections. Attach the required graphs. 46

Explanation / Answer

Q1

-Qhot = Qcold + QCal

Qhot = mass h* Cp ( Tf - Thot)

Qcold = mass c * Cp ( Tf - Tcold)

Qcal = CCal*dT

-50*4.184*(24.81-29.15) = 50*4.184*(24.81-21) + CCal*(24.81-21)

CCal = (-50*4.184*(24.81-29.15) - 50*4.184*(24.81-21))/(24.81-21)

CCal = 29.10 J/°C

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