Title: Cleaning with Chemistry

Sam Redstone

January 30, 2014

Title: Cleaning with Chemistry

Appropriate Level: Students Grades K-8

Abstract: Students will be introduced to the concepts of acid-base chemistry and learn the relationships between pH and reactivity. They will then participate in a hands-on activity to explore the practical uses of this knowledge by using household acids and bases to clean various messes.

Time Required: 40 Minutes

Objectives: Students will develop an understanding of how the pH of a substance affects its reactivity. Due to these pH properties, depending on what the mess is, some household materials clean substances better than others do. Additionally, students will have practice with the scientific process of making observations and taking notes.

Chemical Concepts

Acid-Base Chemistry: Acids and bases react to yield water, with the most fundamental acid-base reaction being the autoprotolysis of water:

H2O + H2O ⇌ H3O+ + OH-.

pH Scale: A set of numbers ranging from 0 to 14 that describes how acidic or basic a solution is. pH values from 0-7 are acidic while values from 7-14 are basic. A pH of 7 is neutral, and the further away from pH 7 a solution gets, the more acidic or basic it is.

Acid: A substance that when in aqueous solution will increase the concentration of protons; its pH is less than 7.

Base: A substance that when in aqueous solution will decrease the number of protons in solution; its pH is greater than 7.

Equipment and Supplies:

Sam Redstone

January 30, 2014

• Old Pennies

• 10-12 Rubber Duckies

• 10-12 Plastic Cups (8 oz. or larger)

• 10-15 cups (4 oz. is fine, cups may be paper or plastic)

• Bar Soap

• 10-12 T. Cocoa Powder

• ¼ Cup Baby Oil

• Lemon Juice (½ cup per group)

• Window Washing Fluid (½ cup per group)

• Cola (½ cup per group)

• Baking Soda and Water (½ cup per group)

• Condensed Tomato Soup (½ cup per group)

• 3”x5” cuts of fabric, any color

•pH meter

•1 Red Cabbage

•Copper-bottomed Cooking Pot

•Magnesium Sulfate (MgSO4)

•Q-tips

•Crushed Doritos

•pH Meter

•Test Tubes (1 per group)

•Test Tube Rack

Figure 1: A pH scale annotated with several household acids and bases.

Sam Redstone

January 30, 2014

Sam Redstone

January 30, 2014

Preparation Work

To be completed by the instructor prior to the experiment.

Time Required: 60 Minutes

“Staining” the materials to be cleaned:

1. To dirty the rubber duck, scrape flakes off of a bar of soap and mix it with hard water until bubbles form. If you live in a region where the water is not high in mineral content, you can make the water “hard” by adding 3-4 scoops of magnesium sulfate (MgSO4). Dip the ducks in the solution being sure that they gather suds. Allow the 10-15 minutes to dry out before beginning the experiment.

2. Add fingerprints to the plastic cups by dipping fingers in baby oil and grasping the cup. Gently shake cocoa powder over the oil prints then shake the cup to remove any excess powder.

3. Mix the cleaning solution of baking soda by adding one tablespoon of baking soda for every 8 ounces of water. This does not need to be done in advance to starting the experiment.

4. Stain the fabric by adding about a tablespoon of crushed doritos to each 3x5” cut of fabric. To do this, crush the doritos with a mortar and pestle and rub the orange color onto the fabric. Shake off any large crumbs that remain.

5. Cabbage juice can be used as an acid-base indicator. To perform this optional demonstration, obtain the cabbage juice by cutting a head of red cabbage in half, submerging it in water and boiling it until the cabbage leaves have lost all color. Filter the juice to remove all cabbage leaves. To use the cabbage juice as a pH indicator, pour 50 mL of it into a beaker and add the substance to be tested. Observe any color change.

Students will try cleaning the previously mentioned products with the following cleaners: lemon juice, tomato soup, cola, window washing fluid and the mixture of baking soda and water.

Instructions for Students:

1. Distribute 5 plastic cups per group, one for each cleaning product. Pour a small amount of each cleaner in the cups and 1-2 q-tips per cup. Have students dab the q-tip in the cleaner and rub it on each object. They will record their observations in the table below.

Optional Demonstrations:

1. At the beginning of the time period, pour some concentrated tomato soup onto the copper pot. Note: the longer the tomato soup sits on the pot, the better cleaning job it will do. At the end of the time period, wash the soup off and ask students to predict what they think will happen.

2. Use the pH meter to show students how scientists measure pH in the laboratory.

Expected Results and Explanation:

It is expected that, due to their reactivity to one another, acids will better clean messes caused by basic substances and vice versa. This is because acids and bases consume each other to yield water. Therefore, adding an acid to an acid will result in a weaker chemical reaction, and the object will not be cleaned as well. Furthermore, the stronger the acid or base is, the more effective cleaner it will be. This is because increasing the concentration of a reactant will increase the rate of the reaction.

The cabbage juice will turn red-purple in color in the presence of an acidic cleaner, while it will turn a greenish-yellow color in the presence of a basic cleaner.

Accommodations for Different Age Levels:

Older students (Grades 6-8) can test the pH of the messes and cleaning supplies with a pH meter or the cabbage juice indicator. They can then use this information to make a more informed prediction as to whether a cleaner will work on a specific mess. Younger students can simply make these predictions without testing the pH and may skip page 6.

Citations:

1. Acid Base Introduction. Khan Academy. http://www.khanacademy.org/science/chemistry/acids-and-bases/v/acid-base-introduction. (Accessed January 12, 2014).

2. pH Scale. https://figures.boundless.com/386/raw/ph-scale.svg. (Accessed January 14, 2014).

3. Acids and Bases: Cabbage Juice pH Indicator. http://www.stanford.edu/group/lpchscience/cgi-bin/wordpress/images/2012/10/Acids-and-Bases-T.pdf . (Accessed January 14, 2014).

Cleaning with Chemistry

Background

Your older sister makes it clear that she does not want you going into her room, but you cant help yourself; she has a palace all to herself! Not only is her bedroom much larger than yours but it is warmer and much more comfortable. Without her knowing, you made the place your own over the past week while she was out of town touring colleges. You were living large in there, eating, drinking and making a general mess. You told yourself you would clean it the day before she returned. The problem is, she just called to say that she is returning a day earlier than expected and there is no time to go to the store to buy cleaning supplies! You will have to make do with the household objects you have on hand, and test them to see which materials clean different messes the best.

Table 1: pH values for household cleaning materials.

Solution / pH
Lemon Juice / 2.1
Coke / 2.5
Tomato Soup / 4.4
Doritos / 5.9
Cocoa Powder / 6.0
Soap Scum / 9.7
Window Cleaner / 10.0

Instructions:

Determination of pH using cabbage juice and pH meter:

As a class, you will determine whether each cleaning product is acidic or basic using cabbage juice as an indicator, then you will use the pH meter to determine more specifically what the pH is. Each pair will perform these pH tests on one of the cleaning products. At the conclusion of the class period, the data will be pooled.

1. pH Test with Cabbage Juice Indicator: To perform this test, pour 4-5 mL of the cleaning material into a test tube. If the cleaning product is acidic (low pH) the indicator will turn red, while the cleaner will remain purple if the pH is neutral (pH~7) and turn green-yellow if the cleaner is basic (high pH). Record observations in the table below.

2. pH Test with pH Meter: To use the pH meter, remove the probe from the DI water, rinse it and place it in the solution to be tested. The pH can be recorded once the reading says “stable.” When done, rinse the probe again and place it back in the water.

Table 2: Observed pH values of household cleaning materials. To be completed as a class.

Cleaner / Cabbage Juice Indicator (Color, Acid or Base?) / pH
Lemon Juice
Window Cleaner
Tomato Soup
Baking Soda
Cola

Name:______

Prediction Table (Circle Yes or No)

What to Clean With
What to Clean / Lemon Juice / Baking Soda / Cola / Window Cleaner / Tomato Soup
Rubber Duck with Soap Scum / Yes
NO / Yes
No / Yes
No / Yes
No / Yes
No
Plastic Cup with Cocoa Powder / Yes
No / Yes
No / Yes
No / Yes
No / Yes
No
Fabric Stained with Doritos / Yes
No / Yes
No / Yes
No / Yes
No / Yes
No
Coin Collection / Yes
No / Yes
No / Yes
No / Yes
No / Yes
No

Observation Table (Circle Yes or No)