Question

post lab questions

1. what is the mole ratio of hydrogen peroxide to permanganate ion in the balanced chemical equation determined in question #2 on your data sheet? how many moles of hydrogen peroxide will be oxidized by .0045 moles of potassium permanganate in an acidic solution?

mole ratio = 5 h₂o₂ / 2 mno₄⁻ × 0.0045 moles = 0.01125 moles h₂o₂

1. review the procedure.

a. was it necessary to know the exact volume of hydrogen peroxide solution added to the flask in step 3 of the procedure?
why or why not? no because it is more important to know the density of h₂o₂ in order to find the mass %
b. how did the milliliters of h₂o₂ solution measured compare to the number of milligrams of the solution?
why were you able to use this comparison?
c. was it necessary to know the exact volume of water added to the flask in step 3?
why or why not?

Explanation:

Step1: Identify mole - ratio from balanced equation

The balanced chemical equation gives the mole - ratio of hydrogen peroxide ($H_2O_2$) to permanganate ion ($MnO_4^-$) as 5:2.

Step2: Calculate moles of $H_2O_2$

We know the moles of $MnO_4^-$ is 0.0045 moles. Using the mole - ratio $\frac{n_{H_2O_2}}{n_{MnO_4^-}}=\frac{5}{2}$, we can calculate the moles of $H_2O_2$ as $n_{H_2O_2}=\frac{5}{2}\times n_{MnO_4^-}$. Substituting $n_{MnO_4^-}=0.0045$ moles, we get $n_{H_2O_2}=\frac{5}{2}\times0.0045 = 0.01125$ moles.

2a

In a titration or reaction - based experiment to determine properties like mass percentage of $H_2O_2$, knowing the density of $H_2O_2$ solution is more important than the exact volume added initially. The mass of $H_2O_2$ can be calculated from density and volume, and then used to find mass percentage. So, it is not necessary to know the exact volume added to the flask in Step 3.

The volume of the $H_2O_2$ solution in milliliters ($V$) and the mass of the solution in milligrams ($m$) are related by the density ($
ho$) of the solution, $
ho=\frac{m}{V}$. We can use this comparison because density is a characteristic property of the solution at a given temperature and pressure, and it allows us to convert between volume and mass.

If the water added is just a diluent and does not participate in the stoichiometric reaction between $H_2O_2$ and $MnO_4^-$, then the exact volume of water added is not necessary to know. The reaction stoichiometry depends on the amounts of the reactants ($H_2O_2$ and $MnO_4^-$) and not on the volume of the diluent (water).

Answer:

No, because it is more important to know the density of $H_2O_2$ in order to find the mass %.

2b