Testing for Acids and Bases!

Grade 7

Science Provincial Learning Outcome(s): Physical Science: Chemistry It is expected that students will:

-measure substances and solutions according to pH, solubility, and concentration.

Materials required and approximate cost for a class of 30 students:

-Ammonia (~$1.99) -Baking Soda (~$1.25)

-Clear plastic cups (~$5.99) -Apple Juice (~$2.50)

-2 Heads of Red Cabbage (~$5.96) -Safety Glasses

-Tablespoons -Water

-6 Glass jars -White Vinegar (~$2.69)

Total Cost: $ 23.51

Data Table:

Solution/Item to be Tested Prediction: Acid,

Base, or Neutral?

Colour of the Extract Observation: Acid, Base,

or Neutral?

Approximate pH

Preparation:

1. Coarsely shred the purple cabbage. Boil the cabbage in a full pot of water for about ten minutes. Strain the

cabbage and refrigerate the cabbage water until needed. When it is time for the lesson, divide the cabbage

juice up into containers so that each table group has about 2 cups of liquid.

2. Fill plastic cups with no more than 3 tablespoons of each of the substances to be tested: Baking soda and

water mixture, lemon juice, water, ammonia, soda water, vinegar

Instructions/Procedure:

1. Have students brainstorm what they know about acids and bases and write their responses on the board.

2. Introduce some information about acids and bases, and let them know what they will be doing in the lab

(testing different household items to determine whether they are acids or bases).

3. Students are to work in groups of 6. Have students number themselves 1-6.

4. At the front of the room there will be 6 cups for each table filled with the household items. Each cup will be

labeled with what item is in it. Person 1 will get the baking soda and bring it back to the table. Person 2 will

get the apple juice, person 3 the water, person 4 the ammonia, person 5 the soda water, and person 6 the

vinegar. Ask students to avoid touching, and drinking the materials, as some of them may be toxic and

irritating to the skin. While the students are getting their materials, distribute the predictions and

observations hand-out.

5. Once the table groups have all 6 cups of materials, have students individually observe each of the cups and

predict whether the material inside is an acid, a base, or neutral in the second column of table 2.

6. While students are writing their predictions, pass out the jars of cabbage juice. Ask that no one touches their

jar until they are asked to.

7. After everyone has finished making their predictions, do a demonstration by adding about two tablespoons

of the indicator juice to the mystery solution (Students will have to guess which household item is contained

in the cup after they have performed the experiment).

8. Each student should take turns adding the cabbage juice indicator to their cup (each student is responsible

for one cup). Everyone in the group should be watching each person as they add the indicator so that they

can witness the colour change firsthand. Person 1 should go first, then 2, 3, and so on.

9. After each person adds their indicator to their cup, column three, four, and five of Table 2 should be filled

out. Table 1 will help them figure out whether their materials are acids and bases, and the approximate pH

of their materials.

10. When students have completed their experiment, have them compare the colour of the liquids on their table

to the liquid in the mystery cup and guess what material is in the cup. There is a space on the bottom of their

handout to write their answer. As a class, go over the answers to Table 2 and the answer to the mystery cup

question.

11. At the end of the lab instruct students to have all of their liquids in one cup and one person can dump it out

in the sink.

Safety Considerations:

1. Students will be using ammonia which is a “corrosive” material. Students need to avoid drinking, touching or

putting their faces too close to it.

2. Some of the materials may be irritating to sensitive skin or there may be allergies.

3. Students will need to clear their desks so that none of the materials get knocked over.

4. Students need to wear safety glasses at all times.

Classroom Management Issues:

1. Students may touch the materials before they are asked to. Proactive step: Asking students not to touch the

materials before we hand them out.

2. Students may try drinking the apple juice or other liquids. Proactive step: Reminding students not to drink

the liquids and circulate the classroom.

3. Students may be off task. Proactive step: Circulate around the classroom and make sure all students are

participating.

Checking for Understanding Questions:

1. How did you make your predictions?

2. Which of the materials were acids, bases and neutral? How did you know?

3. What makes a material an acid or a base?

4. What other kinds of household items do you think are acids? bases?

References: http://www.saskschools.ca/curr_content/science9/chemistry/lesson11.html

By Brianne Irving and Krista Flood

Testing for Acids and Bases

Use the table below to help you figure out whether your materials are acids, bases, or neutral, and the approximate pHs.

Table 1:

Colors of Red Cabbage Juice and Different pH values

Approximate pH

2 4 6 8 10 12

Color of Extract

red purple violet blue blue-green green

ACID-----------------------------NEUTRAL----------------------------BASE

Fill in Table 2 with your predictions before performing the experiment and your observations after performing the experiment:

Table 2:

Solution/Material to be

Tested

Prediction:

Acid, Base, or

Neutral?

Colour of the

Extract

Observation:

Acid, Base, or

Neutral?

Approximate

pH

Baking Soda

Lemon Juice

Water

Ammonia

Soda Water

Vinegar

Which one of the above materials is contained in the mystery solution?

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