Chemistry: Green Chemistry: Atom Economy and Safer Solvents Worksheet

Question 1

Define atom economy in your own words. How is atom economy different from percent yield?

Accepted Answer

Atom economy is the percent of reactant atoms that end up in the desired product, based on the balanced chemical equation. Percent yield compares the actual amount of product made to the theoretical amount, so it depends on how well the experiment worked.

Question 2

The reaction A + B -> C has molar masses of A = 30 g/mol, B = 20 g/mol, and desired product C = 50 g/mol. Calculate the atom economy.

Accepted Answer

The atom economy is 100% because the desired product has a molar mass of 50 g/mol and the total reactant molar mass is 30 g/mol + 20 g/mol = 50 g/mol. The calculation is 50/50 x 100% = 100%.

Question 3

The reaction A + B -> C + D has molar masses of A = 60 g/mol, B = 40 g/mol, desired product C = 70 g/mol, and byproduct D = 30 g/mol. Calculate the atom economy for product C.

Accepted Answer

The atom economy is 70% because the desired product has a molar mass of 70 g/mol and the total reactant molar mass is 60 g/mol + 40 g/mol = 100 g/mol. The calculation is 70/100 x 100% = 70%.

Question 4

A student says, "A reaction with 90% yield is always greener than a reaction with 60% yield." Explain why this statement is incomplete.

Accepted Answer

The statement is incomplete because yield is only one part of green chemistry. A 90% yield reaction could still use toxic solvents, require a lot of energy, or have poor atom economy, while a 60% yield reaction might use safer materials and create less hazardous waste.

Question 5

Two pathways can make the same product. Pathway 1 has 45% atom economy and uses benzene as a solvent. Pathway 2 has 80% atom economy and uses ethanol as a solvent. Which pathway is greener based on the information given, and why?

Accepted Answer

Pathway 2 is greener based on the information given because it has higher atom economy and uses ethanol, which is generally safer than benzene. Benzene is hazardous and carcinogenic, so avoiding it is a safer solvent choice.

Question 6

A reaction has a balanced equation: C2H4 + Br2 -> C2H4Br2. The molar masses are C2H4 = 28 g/mol, Br2 = 160 g/mol, and C2H4Br2 = 188 g/mol. Calculate the atom economy.

Accepted Answer

The atom economy is 100% because all reactant atoms become part of the desired product. The calculation is 188/(28 + 160) x 100% = 188/188 x 100% = 100%.

Question 7

A reaction has a balanced equation: C2H5OH -> C2H4 + H2O. If ethene, C2H4, is the desired product, calculate the atom economy. Use molar masses C2H5OH = 46 g/mol, C2H4 = 28 g/mol, and H2O = 18 g/mol.

Accepted Answer

The atom economy for ethene is about 60.9%. The calculation is 28/46 x 100% = 60.9%, so about 60.9% of the reactant mass becomes the desired product.

Question 8

List three properties that make a solvent safer or greener for use in a chemistry lab or industrial process.

Accepted Answer

A safer or greener solvent is less toxic to humans, less harmful to the environment, and less flammable or volatile. Other useful properties include being renewable, recyclable, biodegradable, and effective at lower amounts.

Question 9

Classify each solvent as generally safer or higher concern: water, ethanol, hexane, benzene, and acetone. Briefly explain one classification.

Accepted Answer

Water and ethanol are generally safer choices, and acetone is often a moderate or relatively safer organic solvent when managed correctly. Hexane and benzene are higher concern solvents because hexane can harm the nervous system and benzene is carcinogenic.

Question 10

A process uses 500 mL of dichloromethane for every 10 g of product. Suggest two changes that could make the solvent use greener.

Accepted Answer

The process could be made greener by replacing dichloromethane with a safer solvent if the reaction still works well. It could also reduce the solvent volume, recycle the solvent, or redesign the process to use little or no solvent.

Question 11

The balanced reaction CaCO3 -> CaO + CO2 is used to make calcium oxide. If CaO is the desired product, calculate the atom economy. Use molar masses CaCO3 = 100 g/mol, CaO = 56 g/mol, and CO2 = 44 g/mol.

Accepted Answer

The atom economy for calcium oxide is 56%. The calculation is 56/100 x 100% = 56%, meaning 56% of the reactant mass becomes the desired product.

Question 12

Explain why a reaction that produces only one product often has a high atom economy.

Accepted Answer

A reaction that produces only one product often has high atom economy because most or all of the reactant atoms are incorporated into the desired product. If there are no byproducts, less reactant mass is wasted.

Question 13

A company is choosing between two solvents for a reaction. Solvent X gives 95% yield but is toxic, nonrenewable, and difficult to dispose of. Solvent Y gives 88% yield but is low toxicity, biodegradable, and recyclable. Which solvent would you recommend, and what tradeoff should the company consider?

Accepted Answer

I would recommend considering Solvent Y because it is safer, biodegradable, and recyclable, even though the yield is slightly lower. The company should compare the small loss in yield with the benefits of lower hazard, easier waste handling, and reduced environmental impact.

Question 14

A reaction route is shown as three steps. Step 1 has 90% yield, Step 2 has 80% yield, and Step 3 has 75% yield. Calculate the overall percent yield for the route.

Accepted Answer

The overall percent yield is 54%. The calculation is 0.90 x 0.80 x 0.75 = 0.54, which equals 54%.

Question 15

A chemist redesigns a synthesis from a three-step process to a one-step process. The new process has better atom economy and uses water instead of a chlorinated solvent. Explain how this redesign follows green chemistry principles.

Accepted Answer

The redesign follows green chemistry principles because it prevents waste by improving atom economy and reducing the number of steps. It also uses a safer solvent, water, instead of a more hazardous chlorinated solvent.

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Chemistry: Green Chemistry: Atom Economy and Safer Solvents

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