Observing Chemical Change
Chemistry Cornerstone Laboratory
Chemistry 2 (822), 2017-18

Contents

Last update: Tuesday, September 20, 2016 10:19 AM

Purpose and Objective

The purpose of this experiment is to observe some of the indicators of a chemical change. The objective of the experiment is to be able to determine if a process shows indication of a chemical change.

Introduction

When a chemical change occurs a new substance is produced. One way of determining if a chemical change has occurred is to observe if the properties of the substances before the reaction are different from those after the reaction. Indicators (or clues) that a chemical change has taken place include the formation of gas (bubbles), the formation of a precipitate (solid), evolution of heat (and/or light), and a color change. Burning a candle is an example of a chemical change. Before burning there is a wick, wax, and oxygen. Burning the candle produces new substances (carbon dioxide and water) and also gives off heat.

A physical change involves a change a physical property, but no change in chemical composition. No new substance is produced in a physical change. Dissolving salt in water is an example of a physical change. The phase of the salt is changed from solid to aqueous, but the chemical composition is still salt and water.

Materials

Be certain that you can identify the equipment and reagents listed below, before starting the experiment.

Safety and Waste Management

Liquid “Z” is an acid that must be handled with extra care. If any “Z” touches your skin, wash immediately with cold water. If any “Z” spills on the lab table, pour baking soda on the spill and then wipe clean with a wet paper towel. Mixtures containing “Z” must be neutralized with baking soda before being washed into the sink.

Procedure

Part A.

  1. Obtain small beaker and add a small amount of crystals labeled “X.” Record observations.
  2. Using a graduated cylinder, measure 20 mL of liquid “Y.” Record observations.
  3. Add the “Y” to the crystals in the beaker. Allow the mixture to sit without stirring for 2 minutes and record observations.
  4. Using a stirring rod, stir the mixture to dissolve the crystals in the liquid. Record observations. Is this a physical or chemical change?
  5. Loosely crumple a piece of aluminum foil. Record observations. Is this a physical or chemical change?
  6. Drop the aluminum foil into the beaker containing the solution. Record observations. Is this a physical or chemical change?
  7. Use the stirring rod to prevent the foil from floating, but do not stir the mixture. Record observations.
  8. Clean up. Put all waste materials in the designated container. Wash the lab equipment with soap and water.

Part B.

  1. Pour 20 mL of liquid “Z” into a small beaker. Record observations.
  2. Loosely crumple a piece of aluminum foil. Record observations. Is this a physical or chemical change?
  3. Add the aluminum foil to the liquid in the beaker. Record observations. Is this a physical or chemical change?
  4. Use the stirring rod to prevent the foil from floating, but do not stir the mixture.
  5. Clean up. Pour the contents of your beaker into the designated waste container. Put all waste materials in the designated container. Note: Liquid “Z” is an acid that must be neutralized with baking soda that is in the designated waste container. Wash the lab equipment with soap and water. Wipe your lab table clean. Return all materials to their proper storage places.

Pre-activity Questions

Answer the following pre-activity questions. Record your answers in your laboratory notebook, or on the available report form according to the instructions from your teacher. Your answers can be used to help you write your introduction for your lab report.

  1. What is the difference between a chemical change and a physical change?
  2. Give an example of how you could physically change an apple.
  3. Give an example of how you could chemically change an apple.
  4. List four clues that a chemical change has occurred.

Post-activity Questions

Answer the following questions either in your laboratory notebook or on the post-activity question sheet supplied according to the instructions from your teacher.

  1. Give two examples of a physical change that occurred in the experiment.
  2. a. Give one example of a chemical change that occurred in part A of the experiment.
    b. What did you observe that indicates that a chemical change occurred?
  3. a. Give one example of a chemical change that occurred in part B of the experiment.
    b. What did you observe that indicates that a chemical change occurred?
  4. Write five questions that you would like to have answered about the lab activity.
  5. Answer as many of your questions as possible with the help of your classmates and instructor.

 

 


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Newton South High School, Newton Centre, MA 02459