Question

I did an experiment known as "Identification of an unknown aldehyde and unknown ketone."

First I added 0.2 mL aldehyde, 1 mL ethanol, 49 drops of water, 2 more drops ethanol, and 4 drops of phenylhydrazone in a flask. I put the solution in ice and crystals formed. My end product weighed 0.105 g. Please calculate the percent yield of the phenylhydrazone reaction assuming the aldehyde is the limiting reagent.

Answer 1

Wt of aldehyde used w = density of aldehyde X volume used

w = 1.01 X 0.2 mL = 0.202 g

TheoreticalYield From balenced equation:

120.1 g aldehyde react to phenyl hydrazin producing 210.3 g of phenylhydrazone (product).

Hence, after reaction of 0.202 g of aldehyde wt of product should be as:

= wt of aldehyde X MW of product / MWof aldehyde

= 0.202 X 210.3 / 120.1

= 0.354 g (100% Yield). This is the weight of product which would come after complete reaction between aldehyde and ph.hydrazine.

Now, Experimental Yield:

Obtained wt of product = 0.105 g

Hence, % Yield = 0.105 X 100 / 0.345

% Yield = 30.4%