Green Chemistry Metrics: Atom Economy, E-Factor and Solvent Choice · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
En anglais

Yield hides waste, metrics reveal it

Science · Chemistry · ages 20-21
Name ______________________   Date ____________

  1. Within a stated process boundary, what ratio gives E-factor?

    • Isolated product mass divided by its theoretical product mass
    • Waste mass divided by isolated product mass
    • Stoichiometric desired-product mass divided by total reactant mass

  2. What does atom economy measure?

    • The stoichiometric reactant mass fraction in the desired product
    • The isolated product mass fraction relative to its theoretical maximum
    • The fraction of all purchased process material recovered after purification

  3. An ideal addition forms only the desired product. A substitution forms that product plus a separate byproduct. Why is the substitution's atom economy lower?

    • Substitution always consumes more cooling energy than addition
    • Substitution converts every reactant atom into the desired product
    • Some reactant atoms leave in a separate byproduct

  4. Each route makes 3 kg product. A discards 9 kg solvent and 3 kg other waste; B discards 3 kg solvent and 3 kg other waste. These are all waste streams, including water, with no recovery. Which has lower E-factor?

    • Route A, because its E-factor is 2 rather than 4
    • Route B, because its E-factor is 2 rather than 4
    • They tie, because equal product masses give equal E-factors

  5. For CaCO3 + 2 HCl -> CaCl2 + CO2 + H2O, CaCl2 is the desired product. Molar masses: CaCO3 100, HCl 36.5 and CaCl2 111 g/mol. Calculate atom economy in percent, rounded to the nearest whole number.

    Answer: ______________

  6. A procedure discards 4 kg spent solvent, 6 kg salts and 2 kg other waste. These are all waste streams. Spent solvent is the largest contributor to its E-factor.

    Circle one:   True   False

  7. Recovering a solvent for reuse removes every environmental cost of using it, so recovery energy and residual waste need not be assessed.

    Circle one:   True   False

  8. Solvents A and B give equal conversion and product quality. A has lower health and environmental hazards and 80% recovery; B has higher hazards and 10% recovery. Initial masses, recovery energy and residual disposal costs are equal. Which choice follows?

    • Choose B because recovering less solvent reduces the solvent mass discarded
    • Treat them as equal because conversion alone determines solvent suitability
    • Choose A for lower hazards and greater recovery
LightMySky · lightmysky.comW1-mt_sxO1hLpaUV-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Yield hides waste, metrics reveal it W1-mt_sxO1hLpaUV-s1

  1. Waste mass divided by isolated product mass · E-factor compares measured waste with isolated product mass. Its value depends on which waste streams the stated boundary includes.
  2. The stoichiometric reactant mass fraction in the desired product · Atom economy uses a balanced equation to compare desired-product mass with total stoichiometric reactant mass. Isolated versus theoretical product describes yield.
  3. Some reactant atoms leave in a separate byproduct · The separate byproduct contains reactant mass that does not enter the desired product. Cooling energy is outside the atom-economy calculation.
  4. Route B, because its E-factor is 2 rather than 4 · A generates 12 kg waste, so E = 12/3 = 4. B generates 6 kg waste, so E = 6/3 = 2. B has the lower E-factor.
  5. 64 · Multiply the HCl molar mass by its coefficient of two. Atom economy = 100 x 111/(100 + 2 x 36.5) = 64.16%, which rounds to 64%.
  6. False · The salt waste is 6 kg, larger than the 4 kg solvent waste and 2 kg other waste. Salts contribute most in this procedure.
  7. False · Recovery can reduce solvent waste, but it can consume energy and leave residues. Those effects remain part of a process comparison.
  8. Choose A for lower hazards and greater recovery · The stated reaction performance and costs are equal. A has both lower hazards and greater recovery, so these data favor A.
Worksheet · LightMySky