PRELABORATORY ASSIGNMENT: CALORIMETRY 1. An empty calorimeter had a mass of 18.2

Question

PRELABORATORY ASSIGNMENT: CALORIMETRY 1. An empty calorimeter had a mass of 18.2531 grams. When water having a temperature of 18.7 C was added, the calorimeter plus water was found to have a mass of 69.1045 grams. A quantity of water having a temperature of 73.4°C was added to the cooler water, and the temperature at the instant of mixing was determined to be 45.5 oC. The mass of the calorimeter plus the mixture of warm and cool water was 123.4651 grams. Determine the heat capacity of the calorimeter TtmPM .atu 18.7.1 ,%,IS , Lesc (cold) Co (s8.yau.s-583 Answer:-25.9 2. A 55 mL. sample of 1 M hydrobromic acid solution was diluted to 100 mL and poured into the calorimeter from problem #1. The initial temperature of the hydrobromic acid in the calorimeter was 20.1 , when 2.8102 grams of solid KOH was added to the hydrobromic acid in the calorimeter, a neutralization reaction occurred, and the temperature of the resulting 0.5 M KBr solution rose to 37.0 C. The total mass of the solution was 107.3482 grams, and the specific heat of the solution was 4.05 Joules gram "C'. a) Write the balanced chemical equation for the neutralization reaction. b) Determine the number of moles of water formed in the reaction. Answer: EXPERIMENT 10 CALORIMETRY page 217

Explanation / Answer

a)

balanced reaction for HBr + KOH

HBr + KOH = H2O + KBr

this is 1:1

add phases

HBr(aq) + KOH(aq) = H2O(l) + KBr(aq)

b)

moles of water formed

mol of acid = MV = 1*55 = 55 mmol = 55*10^-3 mol = 0.055

mol of base = mass/MW = 2.8102/56.10564 = 0.05008

Clearly, there is excess acid

so mol of water is based on KOH

mol of KOH = mol of water = 0.05008 mol of water

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