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Author Topic: molar heat of neutralization  (Read 6565 times)

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molar heat of neutralization
« on: October 23, 2007, 08:28:44 AM »

A student was asked to determine the enthalpy change for a chemical reaction using a constant pressure calorimeter, that is, a polystyrene cup, and and ordinary lab thermometer.  The reaction under consideration is the neutralization of ammonium chloride by sodium hydroxide.

NH4CL + NaOH ===> NH3 + NaCl + H2O

a) In an effort to collect accurate data, the student decided to first measure the specific heat of the calorimeter.  To do this, she added 50.0 g of room temperature water to the foam cup; both were at the same temperature, 21.2 degrees C.  She then added 50.0 g of warm water, 78.5 degrees C, to the contents of the cup.  The highest temperature that the mixture achieved after thorough mixing was 48.5 degrees C.  What is the heat capacity of the calorimeter in kilojoules?

I determined the heat capacity to be 20.69kJ/degree C.

b)  The student than added 50.0 mL of 2.00M NH4Cl solution (density= 1.04g/mL) to the dried calorimeter followed by 50.0mL of 2.00 M NaOH solution (density= 1.02g/mL).  The initial temperatures of both solutions and the cup were 22.3 degrees C.  The final maximum temperature fo the reaction mix, after stirring, was 23.5 degrees C.  Calculate the molar heat of neutralization of ammonium chloride by sodium hydroxide.  Assume that the specific heat of these acid and base solutions is equal to that of water, 4.184 Jxg^-1xdegrees C^-1.

Based on my calculations, there are 0.1 moles of NH4+ and 0.1 moles of OH-.  From there, however, I don't know what to do. *delete me*

c)  Was measurement of the cup's heat capacity necessary? Explain.

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