Stoichiometry and the Chemical Equation
(Reaction of Hydrogen Peroxide and Bleach)



Purpose and Method:

When hydrogen peroxide, H2O2(aq), is mixed with bleach, active ingredient, NaOCl(aq), oxygen gas is formed, O2(g). Based on the amount of reactants used and the amount of product(s), determine the stoichiometry of the chemical reaction.
Running two sets of reactions; SET A where the amount of bleach is held at a constant 4.0mL; secondly SET B where the amount of H2O2(aq) is held at a constant 4.0mL. Determine for each reaction set at what volume, of the reactant that is varied, does the reaction stop; or in other words, O2(g) stops forming as one of the reactants is consumed.
When all of the H2O2(aq) is consumed, the volume of O2(g) produced levels off. There is a point when more bleach is added, no more O2(g) is formed. The situation on the left-hand side of the point where the volume of O2(g) produced levels off, the bleach(NaOCl(aq)) is the limiting reagent; likewise on the right-hand side of this point, the H2O2(aq) is the limiting reagent.
For SET A: When the amount of bleach is held constant at 4.0mL, find experimentally, the UNKNOWN amount of the H2O2(aq) solution when formation of O2(g) halts. With these equations we can find the ratio: moles of H2O2 to moles of NaOCl.

(4.0mL NaOCl(aq) in solution)(5.25g NaOCl(aq)/ 100g solution)(1g /1mL)(1 mole/MM of NaOCl(aq))=
# moles of NaOCl(aq) in 4.0mL of solution

(UNKNOWN mL H2O2(aq) in solution)(3g H2O2(aq) / 100g solution)(1g /1mL)(1 mole/MM of H2O2(aq)) =
# moles of H2O2(aq) in 4.0mL of solution
For SET B: When the amount of H2O2(aq) is held constant at 4.0mL of solution, find experimentally, the UNKNOWN amount of the NaOCl(aq) when formation of O2(g) halts. With these equations we can also find the ratio: moles of H2O2 to moles of NaOCl.

(4.0mL H2O2(aq) in solution)(3g H2O2(aq) / 100g solution)(1g /1mL)(1 mole/MM of H2O2(aq)) =
# moles of H2O2(aq) in 4.0mL of solution

(UNKNOWN mL NaOCl(aq) in solution)(5.25g NaOCl(aq)/ 100g solution)(1g /1mL)(1 mole/MM of NaOCl(aq))=
# moles of NaOCl(aq) in 4.0mL of solution

After the ratio is determined, then this equation needs to be balanced:


DATA:
After measuring the volumes of H2O2(aq) & Bleach(NaOCl(aq)) carefully(bottom of the meniscus), then placing them both into an Erlenmeyer flask(the two solutions are not in contact). The two solutions where allowed to react producing O2(g) from the sealed Erlenmeyer flask into an water-filled, inverted 100mL graduated cylinder by means of a rubber tube. The volume of O2(g) was then measured and recorded.
For both SET A & SET B we used batch #3 of H2O2(aq), and batch #3 of Bleach(NaOCl(aq)).

Reaction SET A: Volume of O2(g) as volume of H2O2(aq) is varied & volume of bleach is constant.
Set A Volume of H2O2(aq) Volume of Bleach Volume of O2(g)
Run 1 1.5mL 4mL 34mL
Run 2 2.5mL 4mL 61mL
Run 3 3.5mL 4mL 72mL
Run 4 4.5mL 4mL 72mL
Run 5 5.5mL 4mL 72mL
Run 6 6.5mL 4mL 72mL
Run 7 7.5mL 4mL 72mL
Run 8 3.0mL 4mL 70mL
Run 9 3.2mL 4mL 70mL

Reaction SET B: Volume of O2(g) as volume of is bleach varied & volume of H2O2(aq) is constant.

Set B Volume of H2O2(aq) Volume of Bleach Volume of O2(g)
Run 1 4mL 1.5mL 26mL
Run 2 4mL 2.5mL 45mL
Run 3 4mL 3.5mL 65mL
Run 4 4mL 4.5mL 81mL
Run 5 4mL 5.5mL 90mL
Run 6 4mL 6.5mL 91mL
Run 7 4mL 7.5mL 89mL
Run 8 4mL 5.0mL 88mL
Run 9 4mL 5.2mL 91mL
Run 10 4mL 5.1mL 87mL

Results:

With the ratio of moles of H2O2 to moles of NaOCl experimentally determined, we approach the non-balanced equation:



As the ratio of moles of H2O2 to moles of NaOCl is 1:1, the coefficients of H2O2 and NaOCl could be 1:



To balance this reaction equation, the coefficients of H2O, O2 and of NaCl are also1:




Discussion:

The mole ratio in SET A agreed with SET B. The difference in the moles of H2O2 and NaOCl to obtain the aforementioned ratio in reaction SET B was very small(.0001 moles). This could be attributable to experimental error. The variance of the volume of O2(g) at 5.5mL, 6.5mL, and 7.5mL in reaction SET B was also quite small(90mL, + /- 1mL). This could also be attributable to experimental error.
The stotchiometric coefficients of a particular reaction equation:


were obtained through experimental means. Specifically determining the mole ratio of H2O2 to NaOCl by varying each reactant while holding the other constant.