Stoichiometry and Calorimetry
Name_______________
This lab will allow you to study the stoichiometry and enthalpy changes of a
reaction. You will establish the stoichiometry for the reaction between
sodium sulfite and household bleach. You will mix the reactants in a series
of volume ratios and measure the temperature change in each case with a
combined volume of 24ml for each trial.
Two possible reactions
H2O + 2NaOCl + Na2SO3  Na2SO4 + Cl2 + 2NaOH
NaOCl + Na2SO3  NaCl + Na2SO4
The combination that gives the greatest value of change of H should have a
stoichiometric ratio of sodium hypochlorite to sodium sulfite that is either
2:1 or 1:1
Procedure
1.Prepare your calorimeter
2.Label each of two 25ml graduated cylinders as Na2SO3 and NaOCl
3.Mix them in the following manner:
-always place the reactant with the larger volume in the calorimeter first
-put the lid with the thermometer on to record the initial temperature
-remove the lid and place the second reactant in and replace the lid and
thermometer immediately and take the 2nd temperature
Mixing volumes
Trial
NaOCl
Trial 1
18
Trial 2
16
Trial 3
14.4
Trial 4
12
Trial 5
9.6
Trial 6
8
Trial 7
6
Na2SO3
6
8
9.6
12
14.4
16
18
Data
Trial
1
2
3
4
5
6
7
ratio
3:1
2:1
3:2
1:1
2:3
1:2
1:3
initial temp
final temp
Analysis
1.to find Q use 4.184J/gC x 24g x change in temperature
Remember that is Q=s x m x change in temp
2.to find change in H use the number of moles and the value of Q for each
And do Q/moles= change in H
3.divide your joules by 1000 to get kilojoules
4.figure out which reaction gave your highest change in H and mark it
5.cut and past the correct equation-remember the ratio indicates the
coefficients of NaOCl to Na2SO3
6.If you did not get the right equation of 2:1 and 1:1, you can fix the
problem by just comparing the 2:1 and 1:1 ratios
Trial
1
2
3
4
5
6
7
ratio
3:1
2:1
3:2
1:1
2:3
1:2
1:3
Q(J)
moles Na2SO3
2.5 x 10-3
3.35 x 10-3
4 x 10-3
5 x 10 -3
6 x 10-3
6.65 x 10-3
7.5 x 10 -3
What is the correct ratio and equation for this reaction?
change of H