# Rates of Chemical Reactions Vanderbilt Student Volunteers for Science Spring 2012.

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Rates of Chemical Reactions Vanderbilt Student Volunteers for Science Spring 2012

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 5134 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 sixteen (1 per pair) of the 3.5 oz measuring cups to the 50 mL line with ice. What is a chemical change? A chemical change does change the properties of a substance. One or more new substances are formed in a chemical change. How can you tell when a chemical change has occurred? –Observe a color change, an emission of gas, or the formation of a precipitate. The rate of a chemical reaction is how fast the reaction occurs. Some of the factors that affect the rate of reaction include temperature, concentration, surface area, and catalysts.

II. Effect of Temperature Have the students fill both 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 10 oz clear DRY cups. Make sure students realize the importance of making sure they add the water at the same time and from the same height just above the cup containing the tablet. Then one of the VSVS team says "1,2,3, Go” and on “Go” the students add all the water or ice from their cups to the tablets in the 10 oz cups.

III. Effect of Concentration Add 5 mL of the colored solution to one graduated cylinder and 20 mL to the other. Fill both graduated cylinders to 100 mL mark with water. Hold the graduated cylinders up so students can see the difference in intensity of the red color. Tell students that the 5% (weak) and 20% (strong) vinegar solutions were prepared in a similar way.

III. Effect of Concentration Refer to the vinegar as strong (20%) and weak (5%). Place the 5% cup next to the 5% solution, so that the students are clear which strength they are using. Tell students to place a level spoon of baking soda in each cup. Tell students they should be ready to pour all the contents into the cup on the count of 1,2,3, Go. (This reaction occurs quickly and will clearly show the weak (5%) solution gives fewer bubbles than the strong (20%) solution.)

IV. Effect of Surface Area: Dust in a Flame 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.) 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. More surface area of the particles is exposed to oxygen when the particles are sprayed into the flame.

V. Effect of Surface Area: Experiment Place the two 3.5 oz measuring cups on the plate. Have the students fill the two cups to the 50 mL mark. Tell students to remove two effervescent tablets from the packet. Have students place one whole tablet in the bottom of one of the DRY 10 oz plastic cups. Tell the students to place one tablet into the ziploc bag and crush the tablet. Tell students to shake all the crushed tablet into one bottom corner and cut the other bottom corner off. Then pour the crushed tablet through the bottom cut corner into the other DRY 10 oz plastic cup.

V. Effect of Surface Area: Particle Size Ask students to observe the two tablets now and tell which tablet has more surface area. (The crushed tablet - more of the inside surface of the tablet is now exposed). Ask students which reaction will happen faster. Tell students they should be ready to pour all the contents into the cup on the count of 1,2,3, Go. Have students add all of the water to the tablets.

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. 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, telling them that it is a 1.5% solution of hydrogen peroxide. Tell students that hydrogen peroxide chemically breaks down into oxygen gas and water. Light a splint with a match and shake it out until it is glowing, not flaming. 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 bursts into flame. 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 Catalyst (potato) Add some H 2 O 2 to the cup with the chunk of potato. Bring the cup around to students and ask them what they observe. Explain to students that a catalyst in the potato (catylase) is speeding up the decomposition of H 2 O 2. 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.

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