Question

Show a balanced equation for the redox reaction for the oxidation of paranitrotoluene using chromic acid (H2CrO4) as the oxidizing agent. (Note that the oxidation of state of Cr goes from 6+ to 3+ and the toluene give up 3 H+'s) Calculate the theoretical yield and percentage yield of the acid from the reaction of OXIDATION OF AN ALKYL AROMATIC COMPOUND

Procedure:

Place 1.5 g of the para-nitrotoluene and 8 mL glacial acetic acid in a reflux flask.Pour 12 mL of 25% CrO3 solution into a conical flask and cautiously add 4 mL concentrated sulfuric acid. Pour this mixture slowly down the inside of the condenser, into the reaction flask. Add boiling chips and reflux for 30 minutes. It was later recrystallized with 20 mL of methanol.

Final product 0.6g

PLEASE ANSWER FULLY, I do not know the balanced equation and how to find the % yield.

Answer 1

The reaction mechanism of oxidation of p-Nitrotoluene to p-Nitrotoluic acid shows that 1 mol os p-Nitrotoluene oxidises to 1 mol of p-Nitrotoluic acid

i.e. 137 g p-Nitrotoluene 167 g of p-Nitrotoluic acid

In our experiment we have used 1.5 g p-Nitrotolene. Let us calculate the expected yield of product p-Nitrotoluic acid i.e. a theoretical yield. While calculating expected yield i.e. theoretical yield we consider that all the mass or weirht of reactant is reacted and converted into the expected product only even no other product we assume that is not formed.

But in actual experiment it is rare case i.e no 100% conversion takes place always. So most of the time experimental yield is less than theoretical yield. (Many factors are responsible for the low yield like imprper molecular collisions , erros in experimental techniques like faulty improper hating, faulty filtration techniques etc.)

In our experiment the reactant p-Nitrotoluene is a limiting reagent and hence calculations are done with respect to p-Nitrotoluene.

We have, 137 g p-Nitrotoluene 167 g p-Nitrotoluic acid

then, 1.5 g p-Nitrotoluene say 'M_T' g

SO, M_T = (167 x 1.5) / 137

M_T = 1.83 g of p-Nitrotpluicacid

Hence the theoretical yield of product is 1.83 g.

But the actual yield of the product p-Nitrotoluic acid i.e. Practical yield say (Mp) is 0.6 g

The % yield of reaction is calculated as,

% Yield = (Mp /M_T) x 100.

%Yield of p-Nitrotoluic acid = (0.6 / 1.83) x 100

%Yield = 32.79

Hence % yield of the p-Nitrotoluic acid in our experiment is 32.79 %.