hey guys, i need some help with some questions:
1. Naphthalene combustion can be used to calibrate the heat capacity of a bomb calorimeter. The heat of combustion of naphthalene (C10H8) is 40.1kJ/g. When 0.8210g of naphthalene was combusted in a calorimeter containing 1000g water, a temperature rise of 4.21 degrees C was observed. What is the heat capacity of the bomb calorimeter excluding the water?
(What i've got so far is that since heat of combustion is 40.1 kJ/g, so 401 x 0.8210 = 329.221kJ must have been released by naphthalene. Next i think i should use q = ms(delta T) except i'm not sure how we're meant to find the heat capacity of the bomb calorimeter "excluding the water"...can anyone help me out?)
2. Given the following information,
CaO(s) + H20 (l) --> Ca(OH)2(s) delta H = -64.8kJ/mol
How many grams of CaO must react in order to liberate 504kJ of heat?
(I got 7.78 mols of CaO which means m = 435.56g. Does any1 agree?)
3. Thyroxine, an important hormone that controls the rate of metabolism in the body, can be isolated from the thyroid gland. If 0.455g of thyroxine is dissolved in 10.0 g of benzene, the freezing point of the solution is 5.144 degrees C. Pure benzene freezes at 5.444 degrees C and has a value for the molal freezing point depression constant Kf of 5.12 degree C kg mol^(-1). What is the molecular weight of thyroxine?
(I know to use delta Tf = Kf x mass of solute...but i don't understand how to find the mols of benzene so that i can find its molecular weight.)