Properties of Matter: Investigation 2 –
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The non-italicized font represents additional information included to support the teacher’s understanding of the content being introduced within the CELL.
This Investigation is designed to
- teach students how to calculate the density of an object,
- help students explore the chemical properties of the samples that are the same color but have different physical forms,
- promote student discovery of the concept that although an element may have different physical forms, its chemical properties are the same for each form,
- promote student discovery of the concept that although a compound may have different physical forms, its chemical properties are the same for each form, and
- introduce students to the Determination of Density procedure.
Teacher Preparation for the Investigation includes the following. This preparation should be done prior to students arriving in the lab.
- Continue to make available to students the following:
- (1) 100 ml beaker with 60 g of aluminum powder
- (1) 100 ml beaker with 60 g of calcium carbonate
- Ensure that the teacher is the only person who knows what the beakers contain. The teacher will reveal the contents to the students later in this Investigation.
- Continue to make available to students the following:
- a weigh dish or piles of the following materials:
- copper foil
- copper shot
- aluminum foil
- Fill five centrifuge tubes with 12 ml of a 0.2M iron chloride (FeCl3) solution. Label the tubes “iron chloride (FeCl3) solution.”
- Fill five centrifuge tubes with 12 ml of a 0.2 M silver nitrate (AgNO3) solution. Label the tubes “silver nitrate (AgNO3) solution.”
- Fill five centrifuge tubes with 12 ml of acetic acid (vinegar). Label the tubes “acetic acid (CH3COOH).”
- Students should continue to wear rubber gloves while handling any of the contents in the beakers or weigh dishes.
Student Preparation for the Investigation includes having students gather the following materials. This preparation takes place on lab day after student groups have settled at their assigned lab tables.
Note: The materials are listed in students’ SDRs. They are also listed below for your reference.
- (1) triple beam balance
- (13) weigh dishes
- (1) 1000 ml graduated cylinder
- (1) marker
- (8) 2cm pieces of masking tape
- (1) pair of gloves for each student
- (1) 250 ml graduated cylinder
- (1) liter pitcher filled with 500 ml of water
- (1) sample of unknown A through F
- (1) centrifuge tube filled with 0.2M iron chloride solution
- (1) centrifuge tube filled with 0.2M silver nitrate solution
- (1) centrifuge tube filled with vinegar
- (8) test tubes
- (1) lab scoop
- (1) test tube rack
- (1) pair of forceps
- (1) pair of goggles for each student
- (1) glass stir rod
- (1) stopwatch
- (3) plastic eye droppers.
Direct one student from each lab group to collect the materials listed in their SDRs.
- Review how to calculate density using the Calculation of Density procedure.
- Encourage students to reflect on the PreLab video as they move through the procedural steps.
- Explain to students that during the Experiment, every procedural step is important. If one step is skipped, data can become invalid. To help students keep on track, direct them to read each step thoroughly, complete the step, then check it off (Read it – Do it – Check it off).
- Direct students to complete procedural steps in their SDRs.
- Calculate the density for each of the unknown substances.
- Transfer the mass and volume of each unknown substance from Investigation One onto Table A.
- Use the space below for your calculations. Remember, the formula for calculating density is: Density = mass ÷ volume
- Record the density of each substance in Table A.
- After students have discussed the prediction questions within their groups, encourage a larger class discussion. As the discussion proceeds, suggest that students may want to continue their investigation by exploring some chemical properties of samples that have the same color but different physical forms.
Note: These are samples that students may believe to be the same compound or element, but in a different physical form.
- Discuss whether a chemical reaction could be used to help to answer the question of whether two physically different samples were the same substance.
- Facilitate student thinking by directing students to Table B of their Investigation Two Data Record.
Note: Students will use the table to submit some of the samples they believe to be the same element or compound to a chemical reaction.
Note: It is likely that students will have grouped the following samples together based on color or texture. Table B in the Investigation Two Data Record has been constructed with these combinations in mind.
- Samples C and E are all white
- Samples A and D are shiny brown.
- Samples B and F are grey.
- Test your prediction.
A. Locate Table B. The second column describes which compound will be added to each unknown. The third column describes how to test each unknown substance.
B. Test and Observe each combination for an initial reaction. Follow the procedure for each sample on Table B. Use the stopwatch to begin timing your reaction for 10 minutes.
C. Record: Write your initial observations in Table B in the Observation 1 column.
D. Record: After 10 minutes has passed, determine whether a chemical reaction occurred (bubbles or color change). Write your answers in Table B in the Observation 2 column.
- After students have performed the tests for chemical reactivity and discussed their results and conclusions, reveal the identity of substances including their chemical symbols or formulas. Use the following table to write the identity of each substance on the board.
Let students know your expectations for clean up. Ask them to clean up.