Testing Household Chemicals

Vanderbilt Student Volunteers for Science

Training PresentationFall 2009

Important!!

• Please use this resource to reinforce your understanding of the lesson! Make sure you have read and understand the entire lesson prior to picking up the kit!

• We recommend that you work through the kit with your team prior to going into the classroom.

• This presentation does not contain the entire lesson—only selected experiments that may be difficult to visualize and/or understand.

I. Introduction

• Please see manual for detailed

explanations.

• What is a physical property? What is a

chemical property?

• Tests: solubility, acid/base, presence of

carbonate ion, presence of starch

II. Set-Up• Divide students into pairs. Distribute one iodine dropping bottle, one

#1 and one #2 Ziploc bag, one well plate, one pie pan, and one observation sheet to each pair of students and to the VSVS volunteer leading the experiment.

• Tell the students to remove all materials from the Ziploc bags and place them neatly on their desks without opening any yet.

• Explain the observation sheet and instruct the students to set-up their well plates in the same order.

• Have students look at the 24-well plate and the instructions on the Household Chemicals Observation Sheet.

• Show the students how to find the letters A, B, C, and D and the numbers 1-6 on the 24-well plate. Then show them how to match the letters and numbers with the lab sheet grid.

• While this is being done, another volunteer should copy the observation sheet onto the board to record class data.

• Emphasize the importance of recording detailed observations. Later, this will make the identification of the “Unknown Chemical Mixture” easier.

IIa. Observing Some Physical Properties

• Tell each pair to place the containers of sugar and powdered sugar side by side at the top of piece of black paper.

• Then they should use the small scoop to put some of each substance on the black paper directly below the container. Stress the importance of wiping the scoop off before changing powders.

• Have the students use their hand lens to examine the sugar and the powdered sugar. Discuss the difference between crystals and powders.

IIa. Observing Some Physical Properties

• Have the students take the containers of solids from Ziploc bag #2 and place them side by side along the middle of the piece of black paper.

• Tell them to use the small scoop and place some of each solid directly below their container. Stress again the importance of wiping the scoop off before changing powders.

• They should observe the powders through the hand lens. Do they see crystals or powder? If they see crystals, are they large or small?

• Tell them to record observations in the appropriate box in the first row on the data sheet.

IIc. Testing the Known Household Chemicals

• Tell the students to place 1 scoop of the powders in the appropriate wells as indicated on the observation sheet. Stress again the importance of wiping the scoop off before changing powders.

• Place 4-5 drops of water in the first row of powders and stir with a different toothpick for each powder.

• After stirring, keep the toothpick in the well until it is needed for the next liquid. This way the toothpicks will not be contaminated with another powder.

• Instruct students to record their observations in the appropriate spaces on their sheets. (Does it fizz, change color, dissolve?) Record class observations on the board.

IIc. Testing the Known Household Chemicals

• Test the acidity of the solutions in row one.

• Dip the toothpick into the well and place a few drops on each of the pieces of red and blue litmus paper.

• Record the color changes.

IIc. Testing the Known Household Chemicals

• Place 4-5 drops of vinegar in the second row of powders and stir with the toothpick.

• Record observations as before.

IIc. Testing the Known Household Chemicals

• Place 4-5 drops of iodine solution in the third row of powders and stir with the toothpick.

• Record observations.• Have students return the

#1 ziploc bag powder contents to the bag, leaving the liquids and litmus paper out for use in the next section.

IId. Testing an Unknown Household Chemical

• Distribute the contents of the #3 Ziploc bag (Unknown Household Chemical: A and B).

• Tell the students that the “Household Chemicals” is actually one of the Known Powders, but they must identify it.

• Instruct the students to examine the powder with their hand lens.• Record observations. Have them predict what Known Powder it might be.• Have the students place 1 scoop of the “Household Chemicals” in the appropriate

column of their well plates.• Repeat steps of “Testing the Known Powders”.• Record all observations.• Ask the students to compare the results of the “Household Chemicals” reactions with

those of the Known Powders and try to determine which powder it is. Have them record their decisions.

• Tell the students what Known Powders are “Household Chemicals” A and B– Household Chemicals A= Baking soda– Household Chemicals B= Cornstarch

• Collect the “Household Chemicals” bags. If there is no more time left, collect the well plates, rinse them out in a sink (either in the classroom or in the restroom). Then place them all in the Ziploc bag. Tell the students to return the other materials to the appropriate bags. Collect the #1 and #2 bags.

IIe. Testing an “Unknown Mixture” (Optional)

• Distribute one of the Unknown Mixture containers from Ziploc bag #4 to each pair along with a clean 24-well plate

from the other set of 16 24-well plates.

• Explain that the purpose is to identify the “Unknown Mixture” by comparing its physical and chemical properties to

those of the known powders.

• Ask: What is a mixture? (A mixture is a combination of two or more substances, each of which retains its own

properties and can be separated from the other. The “Unknown Mixture” consists of two of the Known Powders.

The goal is for the students to determine which two powders are present in the mixture.)

• Tell students to place 1 scoop of the Unknown Mixture on the black paper and examine the powder with their

hand lens. Tell them to record what it lookslike in the first box of the observation sheet for the Unknown Mixture.

• Have the students place 1 scoop of the Unknown Mixture in wells 2, 3, 4 of the first row of the 24-well plate.

• Tell them to add 4-5 drops of the corresponding liquid (water, vinegar, iodine) and to test with litmus paper.

• Record all observations.

• Ask the students to compare the results of the Unknown Mixture reactions with those of the Known Powders and

try to determine which two powders make up the Unknown Mixture. Have them record their decisions.

• Reveal the true identity of the Unknown Mixture to the students: Unknown Mixture is sugar and cornstarch.

(Actually the powdered sugar that you buy is a mixture of powdered sugar and cornstarch.)

• Rinse out the well plates used for the Unknown Powder and place them in the Ziploc bag. Put everything back in

the box and return it to the VSVS lab.