Rates of Chemical Reactions Vanderbilt Student Volunteers for Science Fall 2016

Kit Clean-Up and Return It is important that all items be returned to the kit box. Be sure to collect all instruction sheets (in sheet protectors) and put them back in the kit box. Be careful not to place wet objects in kit. Kits should be returned to SC 5234 as soon as you return to campus from the school.

I. Introduction Set up: While one volunteer goes through the Introduction, the other volunteers need to fill 12 3.5 oz measuring cups (1 per group of 3) to the 50 mL line with ice. Ask class: “What is a chemical change?” Explain: “A chemical change does change the properties of a substance. One or more new substances are formed in a chemical change.” Ask class: “How can you tell when a chemical change has occurred?” Explain: “A color change, an emission of gas, or the formation of a precipitate. A precipitate is solid that comes from the mixture of two liquids. It can make the liquid look cloudy, or it could sit on the bottom.” The rate of a chemical reaction means how fast the reaction occurs. Factors affecting the rate include: temperature, concentration, surface area, and catalysts.

II. Effect of Temperature Hand out to each group of 3: Two tall clear cups Two small translucent cups – 1 containing ice and the other empty One packet of two effervescent tablets One plate Have the students fill both small cups to the 50 mL line with water and place them on the plate. Tell students to cut open one end of the packet of effervescent tablets. Have students add a whole tablet to each of the clear DRY cups. Make sure students realize the importance of adding the water at the same time. Then one of the VSVS team says "1,2,3, Go” and the students add all the water and ice water from their cups to the tall clear cups containing the tablets.

III. Effect of Concentration Demonstration of what Concentration means: Add 1 scoop of Koolaid powder to one of the cylinders Add 4 scoops to the other cylinder. Add water to both graduated cylinders and fill to the 100 mL mark. Hold the graduated cylinders up so students can see the difference in darkness of the purple color. Tell students that the 5% (weak) and 20% (strong) vinegar solutions (which will be used in the following demonstration) were prepared in a similar way. Explain that concentration is the measure of how much of one substance is dissolved in another.

III. Effect of Concentration Student Activity: Hand out to each group: Two cups, A bottle of 20% vinegar A bottle of 5% vinegar Baking soda Refer to the vinegar as strong (20%) and weak (5%). Place the cups next to the solutions, and make sure the students are clear which strength they are using. Tell students to place a small spoonful of baking soda in each cup. Stress that there should be the SAME amount of baking soda in each cup. Tell students they should be ready to pour the entire contents (vinegar) into the cups on the count of “1,2,3, Go.” Ask: “In which cup did the reaction occur with more bubbles?” Explain: “This reaction occurs quickly and with more bubbles in the strong (20%) solution and slower with fewer bubbles in the weak (5%) solution. This shows that the 20% (the solution of higher concentration) had more substance to react and therefore reacted faster.

Demo: What is Surface Area? Surface area is the exposed surface of an object. Show students a flat piece of paper (in the coffee can), and ask students how much of the paper exposed to air. They should say all of it. Now crumple the paper into a small ball, and ask students how much of the paper is exposed to the air. Make sure they understand that the crumpled paper has a smaller surface area than the flat paper.

IV. Effect of Surface Area: Dust in a Flame Demonstration: Show the students the lycopodium "dust” powder. Place a small pile of powder on the aluminum pan and attempt to light it with a match. (Depending on how long the match is held to the powder - it will either not burn or will burn enough to char a little.) Explain: “There is very little surface area for the dust to be reacted with, and so, very little reaction takes place.” Light the tea candle and place it on the aluminum pan. Load the pipette with a small amount of dust powder (enough to fill the tip). DO NOT turn the pipette upside down. Hold the pipette so the tip is near the flame and squeeze the pipette bulb to release the lycopodium powder into the flame. There will be a flash of fire. Explain: “More surface area of the particles is exposed to oxygen when the particles are sprayed into the flame. Therefore, more of a reaction takes place faster. *Possible anaolgy: “When waiting to get lunch in the cafeteria, there may be only one station for getting lunch open. It takes longer for everyone to get food in this situation. If there were multiple places to get food, everyone would get to eat much sooner. This is a similar situation. The powder in the air is more spread apart and more open, so the reaction happens faster.”

V. Effect of Surface Area Experiment: Hand out: Two tall clear 10 oz cups A ziploc bag Tablet packet Scissors Note: Students should already have two 3.5 oz. cups marked for 50 mL from first experiment Students: Fill the two cups small cups to the 50 mL mark Remove two effervescent tablets from the packet. Place one whole tablet in the bottom of one of the tall clear dry 10 oz plastic cups. Place one tablet into the ziploc bag and crush the tablet. Shake all the crushed tablet into one bottom corner of the bag and cut the other bottom corner off. Then, pour the crushed tablet through the cut corner into the other tall clear dry 10 oz plastic cup. *Continued on next slide

V. Effect of Surface Area: Particle Size Ask: Which of the two tablets has more surface area? (The crushed tablet - more of the inside surface of the tablet is now exposed). Which reaction do you predict will occur faster? Make sure students are ready to pour in the water from the smaller cups. Count them down 1,2,3, Go and have them add all the water to the tablets. Ask them which reaction they observed to happen faster.

VI. Effect of Surface Area Dust Can Explosion Show students the "dust can”. Light the tea light candle and place it in the coffee can. Load the pipette with a small amount of dust powder (enough to fill the tip). DO NOT turn the pipette upside down. Show the pipette to the students. Tell students that there is a hole in the side of the can. Ask students to predict what will happen when you 'blow’ the dust into the can. Holding the pipette at an angle (aiming down with about a 30°angle), place the pipette in the hole (make sure the pipette is snug). Place the lid on the can. Quickly, before the candle dies from lack of oxygen, squeeze firmly on the pipette and leave the pipette in the hole after squeezing. There will be a flash of fire, a loud explosion, and the lid will blow off the can. Note: If the explosion does not happen on the first try, please try again. Some groups have to try this three or four times to achieve the desired results.

VII. Effect of a Catalyst Show the clear bottle containing hydrogen peroxide to the students. Tell them that it is a 1.5% solution of hydrogen peroxide. Tell students that hydrogen peroxide chemically breaks down into oxygen gas and water without any added chemicals. Light a splint with a match and shake the flame out until it is glowing, not flaming. Put the splint over the jar, and show the students how it does not reignite the flame. Tell students to watch what happens when a spoon of manganese dioxide is added to the jar. As soon as you see vigorous bubbling insert the glowing splint into the top of the jar. Observe that it relights the splint with a flame. Explain to the students that the Manganese dioxide is a catalyst which breaks down hydrogen peroxide faster into Oxygen and water. Because fire burns oxygen, this creates enough oxygen to relight the flame, even though before there wasn’t enough. DO NOT dump the jar containing the manganese dioxide down the drain! Close the lid and bring it back to the lab for disposal.

VII. Effect of a Biological Catalyst (potato) Add some H2O2 to the cup with the chunk of potato. Bring the cup around to students and ask them what they observe. Explain that a catalyst in the potato called catylase is speeding up the decomposition of H2O2. Point out that a catalyst is not changed during a reaction. Leave the potato with the teacher and tell them to observe the potato tomorrow to see if there are any changes to the potato. Hopefully, they will observe no change in the potato to conclude that the catalyst is not used up during the reaction.