Prelab Questions: Solution Calorimetry and Hess\'s Law 1. What is/are the purpos
ID: 1027519 • Letter: P
Question
Prelab Questions: Solution Calorimetry and Hess's Law 1. What is/are the purpose(s) of the Styrofoam cups in this experiment? 2. What are some assumptions that we make during this experiment in order to calculate the enthalpy of formation of ammonium sulfate? [Hint: the answer may be found in the Introduction section.] 3. Calculate the mass of the solution used if a student added 35.569 grams of ammonium sulfate to enough water to give 80.0 mL of solution. The density of the solution was 1.00 gmL. [Hint: The mass of ammonium sulfate is not needed for this calculation.] How many significant figures should your answer have? 4. For the neutralization reaction (i.e., Part I of this experiment), calculate the number of moles of the limiting reactant when 25.0 mL of 2.085 M HS0, (a) is mixed with 50.0 mL of 1.873 MNH, (aq) using the molar ratio of the reaction. Show your work with the correct units and number of significant figures 5. If a student calculated the number moles of limiting reactant for the above neutralization reaction (See Question 4 above) to be 0.00568 moles of ammonium sulfate and the heat (i.e., Q) of the reaction to be 5680 J, calculate the enthalpy change of this reaction. Show your work with the correct units and number of significant figures.Explanation / Answer
1)
The purpose of the Styrofoam cups in this experiment is as follows:
i) The Styrofoam cup in a calorimeter reduces the amount of heat exchange between the water in the cup and the surrounding air.
ii) The Styrofoam cup provides insulation when materials are mixed inside of it
iii)The Styrofoam cup is a container with good insulated walls to prevent heat exchange with the surrounding.
2.
Assumptions :
(a) heat liberate = heat absorbed and no heat loss to the environ ment
(b) reactants react completely.
3)
80mL solution = 80mL water = 80 gm
mass of solution used = 80gm
4.)
2NH3 + H2SO4 ==> (NH4)2SO4
moles of H2SO4 used =25mL*2.085 M/1000mL
=0.052 moles
Moles of NH3 used = 50mL*1.873M/1000mL
= 0.094 moles
2 moles NH3 reacts with 1 mole H2SO4. Moles of NH3 required to react with 0.052 moles of H2SO4 = 0.052*2 =0.104 moles.
So, the limiting reagent is NH3 as it will be completely consumed.