If a student starts with 0.387 g of p-anisaldehyde and ends up with 0.265 g of methyl-E-4-methoxycinnamate, what are their theoretical and percent yields?

1. Write the equation. It isn't necessary to balance everything but you must know how many mols of the prouct you obtain for 1 mol of the reactant.

2. Convert 0.387g to mols. mols = grams/molar mass.
3. Using the coefficients in the balanced equation, convert mols of the reactant to mols of the product.
4. Convert g to mols. g = mols x molar mass. This is the theoretical yield of the methyl E compound.
5. %yield = (actual grams yield/theoreticl yield)*100 = ?

Thanks! However, Do I convert the g I got by dividing by the molar mass of methyl E? The reaction is 1-to-1.

As I outlined it, you convert the para compd to mols. If the rxn is 1:1, you will get that many mols of the methyl E cmpd. Convert that to grams as I wrote; g = mols methyl E x molar mass. That is the theoretical yield of the methyl E.

Then %yield = (0.265 methyl E/theoretical yield of methyl E)*100 = ?

Thank you so much!!! :)

78

To find the theoretical and percent yields, we first need to understand the concept of limiting reagent and actual yield.

1. Determine the limiting reagent:
To find the limiting reagent, we compare the amount of p-anisaldehyde (0.387 g) and methyl-E-4-methoxycinnamate (0.265 g).

p-Anisaldehyde has a molar mass of 136.15 g/mol, so we can calculate the number of moles:
0.387 g / 136.15 g/mol = 0.002840 mol

Methyl-E-4-methoxycinnamate has a molar mass of 178.22 g/mol, so we can calculate the number of moles:
0.265 g / 178.22 g/mol = 0.001487 mol

To find the limiting reagent, we compare the mole ratios of the reactants. The reactants' coefficients from the balanced equation can be used to determine the ratio: p-anisaldehyde reacts with 1 mole of methyl-E-4-methoxycinnamate.

Since the ratio of moles is 1:1, we compare the actual number of moles of each reactant. The reactant with fewer moles is the limiting reagent. In this case, p-anisaldehyde has fewer moles (0.002840 mol) compared to methyl-E-4-methoxycinnamate (0.001487 mol). Hence, p-anisaldehyde is the limiting reagent.

2. Calculate the theoretical yield:
Theoretical yield is the maximum amount of product that can be obtained from the limiting reagent. To calculate it, we need to consider the mole ratio of the limiting reagent and the product.

From the balanced chemical equation, we can see that 1 mole of p-anisaldehyde reacts to produce 1 mole of methyl-E-4-methoxycinnamate.

Since the limiting reagent is p-anisaldehyde and we have 0.002840 mol of it, the theoretical yield can be calculated by multiplying the molar mass of methyl-E-4-methoxycinnamate by the number of moles of p-anisaldehyde:

The molar mass of methyl-E-4-methoxycinnamate is 178.22 g/mol. Therefore, the theoretical yield is:
0.002840 mol * 178.22 g/mol = 0.508 g

So, the theoretical yield is 0.508 g.

3. Calculate the percent yield:
The percent yield is calculated as the ratio of the actual yield (0.265 g) to the theoretical yield (0.508 g) multiplied by 100%:

Percent yield = (actual yield / theoretical yield) * 100%
Percent yield = (0.265 g / 0.508 g) * 100%
Percent yield ≈ 52.1%

Therefore, the theoretical yield is 0.508 g, and the percent yield is approximately 52.1%.