Green Chemistry: Benign by Design!
Facilitator: Milan Sanader “Green chemistry” is a movement to make manufacturing processes that involve chemicals more environmentally friendly and sustainable. A green chemical process is designed from the ground up to have minimal impact on the environment. In other words, a green process is "benign by design". Going green is not only good for the environment but it has also made many companies more profitable. The principles of Green Chemicals are evident in both the STSE features of Nelson Chemistry 11 as well as the lab‐based activities designed for the program. Green Chemistry is based on the following twelve principles*. 1. Prevention It is better to prevent waste than to treat or clean up waste after it has been created. 2. Inherently Safer Chemistry for Accident Prevention Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires. 3. Designing Safer Chemicals Chemical products should be designed to effect their desired function while minimizing their toxicity. 4. Safer Solvents and Auxiliaries The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used. 5. Design for Energy Efficiency Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure. 6. Use of Renewable Feedstocks A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable. 7. Atom Economy Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product. 8. Catalysis Catalytic reagents (as selective as possible) are superior to stoichiometric reagents. 9. Less Hazardous Chemical Syntheses Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment. 10. Reduce Derivatives Unnecessary derivatization (use of blocking groups, protection/ deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste. Page 1 11. Design for Degradation Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment. 12. Real‐time analysis for Pollution Prevention Analytical methodologies need to be further developed to allow for real‐time, in‐process monitoring and control prior to the formation of hazardous substances. *Anastas, Paul & Warner, John. Green Chemistry: Theory and Practice (Oxford University Press: New York, 1998) Nelson Chem Gems Collection
This collection of demonstrations is designed specifically to support the SCH3U curriculum. Many of
these demonstrations are based on student investigations in the text.
Chemical Reactions
Elephant Toothpaste
Concept: decomposition reactions, catalysts
Place a volumetric flask in a large tub. Fill much of the lower portion of the flask with 6% hydrogen
peroxide. Add a few squirts of liquid detergent. Add about ½ teaspoon of dry yeast.
What happens:
Yeast catalyzes the decomposition of hydrogen peroxide into water and oxygen gas. Yeast is a greener
alternative to traditional catalysts used for this reaction (e.g., MnO2, KI). The foam can be tested for
oxygen using a glowing splint.
Can Ripper
Concept: displacement reactions, redox reactions,
Caution: Copper(II) chloride is toxic. Avoid skin contact. Collect and reuse the copper(II) chloride
solution. Recycle the aluminum.
Use a sharp object (e.g., nail) to score a line around the interior circumference of a soft drink can. This
cuts through the plastic liner on the inside of the can. Place the can in a plastic pan to contain spills. Pour
0.5 mol/L copper(II) chloride into the can to a height that is slightly above the line. Wait for about 5
minutes for the oxidation of aluminum to occur. You may begin to small leaks forming at the score line.
Carefully pour off the solution and reuse it. Rip the can apart.
What happens: The copper ion, Cu2+(aq) oxidizes aluminum, weakening the can enough for you to pull it
apart. The reaction doesn’t work if copper(II) sulfate is used. Evidence of copper metal is observed on
the inside of the can.
It’s Only Money
Concept: combustion reactions
Prepare about 25 mL of a 50:50 mixture of ethanol and water. Add 1-2 g of salt. Immerse a $20 bill
(preferably from your class) into the solution. Use tongs to remove the bill. Ignite the bill.
Caution: the volume of alcohol in the room should always be kept at a minimum. Do not allow students
to come near the demonstration table. Student volunteers should not be permitted to conduct this demo.
What happens: Only the alcohol burns. Enough water remains to prevent the bill from burning.
However, the bill will be soggy. Have another one available to return to the person who made the
“donation”.
Page 2 Hydrogen Pop Lab
Concept: balancing chemical equations, mole ratios, limiting reagents
Generate hydrogen gas in one well plate by reacting magnesium with dilute hydrochloric acid. Fill two
thirds of one pipette bulb with hydrogen. Fill one third of another bulb with hydrogen. Generate oxygen
gas in another well plate by decomposing hydrogen peroxide using dry yeast as a catalyst. Fill the
remainder of each bulb almost completely with oxygen gas. Critical: the gas bulbs must remain vertical.
Otherwise, the gases will escape. One drop of water should remain in the bulb to act as a plug to prevent
the gas mixture from escaping. However, Squirt each gas mixture into a flame to see which gives the
loudest “pop”.
Bonding
Gack
Gack is a viscous mixture of corn starch and water. Add about a teaspoon of cornstarch to the palm of
your hand. Slowly add water and mix until the mixture has the consistency of a viscous paste.
What Happens: Under pressure, the paste feels solid. It becomes a "runny" fluid again once the pressure
is released. The application of pressure forces the polymer chains in the starch to align, increasing the
likelihood of intermolecular attractions. These attractions break once the pressure is released. Two
interesting demonstrations of gack can be found at:
http://www.youtube.com/watch?v=hMvxYuZpDpk&feature=fvsr
http://www.youtube.com/watch?v=RUMX_b_m3Js
Predicting Properties of Substances in a Microgravity Environment
Concept: intermolecular attractions, hydrogen bonding .
Hydrogen bonding results in some rather unusual and unpredictable properties of water in a microgravity
environment, as you will see:
(a) Water in microgravity
http://www.youtube.com/watch?v=r7fEHYkGxd0&feature=related
(b) A simple chemical reaction in microgravity:
Alka-seltzer tablet and water in microgravity
http://www.youtube.com/watch?v=bgC-ocnTTto
Solutions
Designs and detergents
Concept: hydrogen bonding, surfactants, surface tension
Add 4 drops of different colours of food colouring to a plate of tap water. Soak a cotton swab into in
liquid detergent. Dip the swab into the middle of the drops and hold it there for about 10 s.
Repeat with milk.
What happens: Soaps and detergents are large ionic compounds that can disrupt the hydrogen bonds
between water molecules. Since milk is mostly water, you would expect soap to have the same effect on
Page 3 milk. However, milk also contains proteins and fat. Protein molecules form hydrogen bonds with water
molecules. Fats do not attract water. Rather, fat molecules clump together in microscopic globules within
the milk. Fat molecules also form attractions with the hydrophobic hydrocarbon chains of the soap ions.
These attractions result in considerable molecular motion, resulting in some spectacular colour blending.
If you really want to be creative, vary the amounts of each colour and where the colour is added. For an
example of what can be done see:
Water Softening technologies
Concept: hard and soft water, ionic exchange resins
The resin from a Brita water filter is opened and removed. A plastic pipette is then filled with the resin.
A sample of hard water is “softened” by passing it through the resin. The effectiveness of the softening
process is tested using EDTA, a reagent that forms complexes with calcium and magnesium ions in the
solution. EDTA is a common ingredient in shampoos because of its ability to complex hardness ions
which prevents them from interfering with the cleaning action of the detergents in the shampoo. A few
drops of eriochrome black T indicator and pH 10 buffer are added to each water sample prior to the
addition of EDTA.
What Happens: Far less EDTA is required to “titrate” the softened water as compared to the untreated
hard water. The Brita resin will also remove some dissolved toxic ions. For example, the resin removes
much of the copper ions from a copper chloride solution.
Supersaturated Solutions
Concept: supersaturation
Gently heat the crystals in a Bunsen burner flame.
What Happens:
As the hydrate decomposes, it dissolves in its own water. The result is a supersaturated solution that is
quite stable. The addition of a seed crystal initiates crystallization. Seal the test tubes and reuse them.
Sodium acetate trihydrate is also commonly used to this activity.
Related web material:
http://www.youtube.com/watch?v=xTIzMaSDZ3k&NR=1 [sodium thiosulfate]
http://www.youtube.com/watch?v=HnSg2cl09PI&feature=fvw [sodium acetate]
Selective Solubility
Concept: “Like dissolves like”.
Fill one quarter of the test tube with mineral oil. Add an equal volume of water. Add two drops of food
colouring to the test tube. Observe the drops carefully as they pass through the mixture. The addition of
an iodine solution colours the mineral oil layer.
What happens:
In this activity mineral oil is a safe replacement for a nonpolar organic solvent like hexane. Food colour
passes through the mineral oil layer in small beads – evidence of the strong hydrogen bonding network
between water molecules within the food colouring. These spheres burst open when the reach the water
layer.
Page 4 Acids and Bases
Milk of Magnesia Neutralization
Concept: neutralization
Add about 400 mL of water, half a teaspoon of milk of magnesia, and a squirt of bromothymol blue
indicator to the large flask. While stirring continuously, add a dilute hydrochloric acid solution until the
flask contents have been neutralized. The addition of slight excess of acid makes the mixture turn clear.
The addition of a sodium hydroxide solution makes the mixture become cloudy again as magnesium
hydroxide precipitates from solution. Using universal indicator is a more spectacular because of the
variety of colours observed. The colours of universal indicator are:
1. Very acidic – Red
2. Acidic - Orange/Yellow
5. Very basic/base/alkali - Purple
3. Neutral – Green 4. Basic/base/alkali - Blue
pH Rainbows
Concept: neutralization
Fill two thirds of a test tube with a mixture of 0.1 mol/L hydrochloric acid and universal indicator. Fill a
small Berol pipette with a saturated sodium carbonate solution. Tilt the test tube and slowly add the
acetate solution to the lower edge of the acid solution. Since sodium acetate is denser, it will sink to the
bottom of the test tube.
What happens: A rainbow of colour is produced as the acid is neutralized because neutralization does not
occur uniformly. Challenge your students to develop of means of controlling the breadth of the rainbow.
The Lemon Shell Game
Concept: neutralization
Add a squirt of phenolphthalein to about 20 mL of a dilute (e.g., 0.1 mol/L) NaOH solution. Use a
syringe (no needle!) to squirt about 5 mL of this solution into a lemon. Wait for a few minutes for the
acid in the lemon to neutralize the NaOH. For fun, mix the lemon with two other lemons and ask students
to predict which contains the pink solution. Cut open all three lemons – no pink.
Properties of Gases
Collapsing Can
Concept: air pressure
Add about 10-20 mL of water to an empty soft drink can. Bring the water to a boil. After steam has been
observed for about 10-15s, quickly invert the can and immerse the opening into a pan of cold water.
What happens: The can quickly collapses because the atmospheric pressure is greater than the air
pressure inside the can.
Making Water Rise
Concepts: thermal expansion of gases, atmospheric pressure, gas solubility
Page 5 A lit birthday candle is standing in a Petri dish. The dish is filled with water. A gas jar is lowered over
the flame. Once the flame is extinguished, water is sucked into the jar. Repeat with two and then three
candles.
What happens:
The height of the water and rate at which it is drawn into the jar increase as the number of candles
increases. The exact cause of this activity remains unclear. Some students may believe that the
consumption of oxygen may create a partial vacuum in the jar. Point out, using the balanced chemical
equation that combustion releases enough gases to offset the lost oxygen. Two factors that certainly are
involved are:
i) Some of the carbon dioxide produced dissolves in the water. However, carbon dioxide solubility in
water is quite low. If this was the only factor, there should not be a significant difference between two
and three candles.
ii) The thermal expansion of the gas inside the jar likely has the greatest influence on the observations.
Expanding Soap
Concept: Charles’ Law
Heat a bar of hand soap in a microwave oven at full power.
What happens:
Water within the soap absorbs microwave energy. This increases the temperature within the bar, causing
the bar to soften. As the internal temperature increases, trapped air and water vapour push outward
causing the soap to expand. For example:
http://www.youtube.com/watch?v=7lAOOwMNodA
Stoichiometry and the Mole Concept
Balloon Stoichiometry
Concepts: mole ratios, stoichiometric amounts, limiting reagents, neutralization
Demonstrate the baking soda/vinegar reaction by adding drops of vinegar to a few grams of baking soda
in a dish. Discuss the factors that limit the extent of the reaction (i.e., the reaction stops once the baking
soda is consumed. Introduce the idea of stoichiometric amounts. Add 1,4,and 7, 10 teaspoons (5 mL, 20
mL, 35 mL, and 50 mL) of vinegar to four empty plastic water bottles. Stretch 4 balloons to improve their
elasticity. Add one teaspoon of baking soda to each of the balloons. Wet the mouth of each balloon with
a small amount of water. This helps make a better seal. Attach the balloons to the bottles. Lift each
balloon so that the baking soda falls into vinegar.
What happens: Carbon dioxide released by the reaction inflates the balloons. The third and fourth
balloons inflate to approximately the same size showing that baking soda is the limiting reagent in these
bottles.
Page 6 The Green Pea Analogy and the Mole
A mole of any pure substance contains 6.02 × 1023 entities (i.e., atoms, molecules, etc). The green pea
analogy is useful to give students some appreciation of how astronomically large this number is.
102 green peas occupy a tea cup
106 green peas fill 1 refrigerator
109 green peas fill 1 three-bedroom house (basement to attic)
1012 green peas fill 1000 houses
1015 green peas fill all buildings in a large Canadian city
1018 green peas cover all Ontario 1 m deep
1021 green peas cover all continents 1 m deep
6.02 × 1023 green peas cover entire planet & 250 other like planets 1 m deep
1027 green peas cover 250 000 planets 1 m deep
1027 atoms = the number of atoms in your body
Conductivity Tester
The conductivity tester shown below costs less than $3 to assemble and is very effective.
Page 7