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Properties of Compounds

Investigation 2 – Lab

Back to Investigation 2

BE PREPARED

Supplies and Equipment:

Class Materials:

8 g cream of tartar
40 g baking soda
100 g salt
200 g sugar
2 L water
1 15 ml centrifuge tube
3 100 ml beakers
1 400 ml beaker
1 triple beam balance 4 weigh dishes
1 lab scoop
1 roll masking tape 1 marker

Group Materials:

4 400 ml beakers
4 stir rods
4 lab scoops
4 weigh dishes
1 100 ml graduated cylinder
1 triple beam balance
1 stopwatch

Individual Materials:

1 Student Data Record

Teacher Preparation:

1. Prepare one compound sample for each group, so that two groups investigate baking soda and three groups each investigate one of the remaining compounds. To do this, follow the table below and label the beakers with masking tape as you obtain the sample.

2. Place the remaining materials distribution point.

3. Divide the class into five cooperative groups.

Instruction:

1. Direct each student group to obtain the following necessary materials from the distribution point: one (1) falcon tube or beaker containing the selected compound, four (4) 400 ml beakers, four (4) stir rods, four (4) lab scoops, four (4) weigh dishes, one (1) 100 ml graduated cylinder, one (1) stopwatch and one (1) triple beam balance.

GET FOCUSED

Investigation Two goes into greater depth into the properties of compounds by introducing the concept of chemical concentration.

INVESTIGATE

1. During this Investigation, each student group will explore the solubility of a compound assigned to them and will learn about the concept of saturation point, the concentration after which a solute is no longer soluble in a solvent. Scientists also refer to this value as the solubility of a solute.

One group will investigate the solubility of cream of tartar, another group will explore salt, a third will explore sugar, and the two remaining groups will investigate baking soda.

To explore the solubility of each of these compounds, students will attempt to dissolve specified amounts of the compound in 100 ml of water at room temperature. After stirring for two minutes, students will observe the contents of the beaker to determine whether the compound sample was soluble in water.

After collecting all of the data in the lab, students will share their results during the PostLab lesson. Students will perform these trials to answer the questions:

Do compounds made of the same elements have the same solubility?

Do compounds made of different elements have different solubility?

Trial 1

2. During Trial 1, each student group will begin the Investigation by attempting to dissolve 0.5 g of their assigned compound in 100 ml of water. To do this, students will use the triple beam balance to obtain a 0.5 g sample of their assigned compound. After measuring the mass of the weigh dish and using it to obtain the correct sample, students will pour the sample into 100 ml of water and stir for two minutes. By observing how much compound remains on the bottom of the beaker, students will be able to answer the following question:

Is 0.5 g of the compound soluble in 100 ml of water?

Note: Sample data sheets for cream of tartar are included. The correct answers for cream of tartar, baking soda, salt, and sugar are summarized in table below on pages 56 and 57 of the Investigation Two lesson plans.

Trial 2-4

3. During these three Trials, students will continue the exploration of the solubility of their assigned compound.

By following the sample masses outlined in the table in Problem 3 of their Student Data Record, students will test the solubility of three additional samples of the compounds.

As students progress from Trial Two to Trial Four, the mass of compound they attempt to dissolve in 100 ml of water will increase. By performing these trials, students will ultimately determine the saturation point of each compound in water. That is, students will determine the concentration after which the solute is no longer soluble in water.

Students will again use the triple beam balance to obtain the necessary samples and will attempt to dissolve each sample in 100 ml of water. When performing these trials, students will again focus on the question: Is the sample of the compound soluble in 100 ml of water?

4. Encourage students to draw conclusions by answering Problem 8 in their Student Data Record.

5. Allow student’s sufficient time to clean up and return their materials to the appropriate location.