In one step in the synthesis of the insecticide Sevin, naphthol reacts with phosgene as shown.
C10H8O+COCl2⟶C11H7O2Cl+HCl
Naphthol Phosgene
A. How many kilograms of C11H7O2Cl form from 2.5×102 kg of naphthol?
B. If 100. g of naphthol and 100. g of phosgene react, what is the theoretical yield of C11H7O2Cl?
C. If the actual yield of C11H7O2Cl in part b is 118 g, what is the percent yield?

Explanation:

A. How many kilograms of C₁₁H₇O₂Cl form from 2.5×10*2 kg of naphthol?

Given data:

Mass of naphthol = 2.5 ×10² kg ( 250×1000 = 250000 g)

Mass of C₁₁H₇O₂Cl = ?

Solution:

Chemical equation:

C₁₀H₈O + COCl₂  → C₁₁H₇O₂Cl + HCl

Number of moles of naphthol :

Number of moles of naphthol = mass/ molar mass

Number of moles of naphthol = 250000 g/ 144.17 g/mol

Number of moles of naphthol = 1734.1 mol

Now we will compare the moles of naphthol with C₁₁H₇O₂Cl.

                    C₁₀H₈O       :         C₁₁H₇O₂Cl

                       1               :                1

                      1734.1         :             1734.1

Mass of C₁₁H₇O₂Cl:

Mass = number of moles × molar mass

Mass = 1734.1 mol × 206.5 g/mol

Mass = 358091.65 g

Gram to kilogram:

1 kg×358091.65 g/ 1000 g  = 358.1 kg

B. If 100. g of naphthol and 100. g of phosgene react, what is the theoretical yield of C11H7O2Cl?

Given data:

Mass of naphthol = 100 g

Mass of COCl₂ = 100 g

Theoretical yield of C₁₁H₇O₂Cl = ?

Solution:

Chemical equation:

C₁₀H₈O + COCl₂  → C₁₁H₇O₂Cl + HCl

Number of moles of naphthol:

Number of moles = mass/ molar mass

Number of moles = 100 g/ 144.17 g/mol

Number of moles = 0.694 mol

Number of moles of phosgene:

Number of moles  = mass/ molar mass

Number of moles =  100 g/ 99 g/mol

Number of moles = 1.0 mol

Now we will compare the moles of naphthol and phosgene with C₁₁H₇O₂Cl.

                    C₁₀H₈O        :         C₁₁H₇O₂Cl

                       1                :                1

                      0.694        :              0.694

                   COCl₂          :             C₁₁H₇O₂Cl

                       1                :                1

                      1.0              :              1.0

The number of moles of C₁₁H₇O₂Cl produced by C₁₀H₈O are less so it will limiting reactant and limit the yield of  C₁₁H₇O₂Cl.

Mass of C₁₁H₇O₂Cl:

Mass = number of moles × molar mass

Mass =  0.694 mol × 206.5 g/mol

Mass = 143.3 g

Theoretical yield  =  143.3 g

C. If the actual yield of C11H7O2Cl in part b is 118 g, what is the percent yield?

Given data:

Actual yield of C₁₁H₇O₂Cl = 118 g

Percent yield = ?

Solution:

Formula :

Percent yield = actual yield / theoretical yield × 100

Theoretical yield = 143.3 g  (from part b)

Now we will put the values in formula.

Percent yield = 118 g/ 143.3 g × 100

Percent yield = 0.82 × 100

Percent yield = 82%

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