What is theoretical yield when 15.6g of bromobenzene & 8.3g of methyl benzoate is used in a Grignard reaction.
Start from an equation
2PhMgBr + PhCOOMe -> Ph3COH
so you need 2 moles of the Grignard reagent to each mole of the ester. As one mole of the PhBr formed from one mole of the Grignard reagent we need 2 moles of the PhBr.
So you need to
1. calculate the molar mass of each PhBr and PhCOOMe
2. calculate the number of moles of each
3. decide which is in excess.
4. calculate the theoretical yield (moles) of Ph3COH
5. calculate the molar mass of Ph3COH
6. calculate the theoretical yield (grams) of Ph3COH
To calculate the theoretical yield in a chemical reaction, you need to determine the limiting reagent. The limiting reagent is the reactant that is completely consumed, thereby limiting the amount of product that can be formed.
In this case, we have two reactants: 15.6g of bromobenzene and 8.3g of methyl benzoate. To determine the limiting reagent, we compare the molar ratios of the reactants to the desired product.
For the Grignard reaction, the bromobenzene is the limiting reagent, as it reacts with the magnesium to form the Grignard reagent. Methyl benzoate acts as a solvent and does not directly participate in the reaction. Therefore, we will focus on bromobenzene for the calculations.
The molar mass of bromobenzene (C6H5Br) is 157.01 g/mol. To convert the mass of bromobenzene to moles, we divide the given mass by the molar mass:
Number of moles of bromobenzene = 15.6g / 157.01g/mol = 0.0994 mol
According to the balanced equation of the Grignard reaction, bromobenzene (C6H5Br) reacts with magnesium (Mg) to form phenylmagnesium bromide (C6H5MgBr) with a 1:1 molar ratio. This means that for every 1 mole of bromobenzene, we obtain 1 mole of phenylmagnesium bromide.
Hence, the number of moles of phenylmagnesium bromide will also be 0.0994 mol.
Finally, to calculate the theoretical yield, we multiply the number of moles of the product by its molar mass. The molar mass of phenylmagnesium bromide (C6H5MgBr) is 181.29 g/mol.
Theoretical yield = number of moles of product x molar mass of product
= 0.0994 mol x 181.29 g/mol
= 18.04 g
Therefore, the theoretical yield in this Grignard reaction is 18.04 grams of phenylmagnesium bromide.