Activity: Chemical Reactions

Introduction

Substances can be characterized by their physical and chemical properties.

Physical properties are those that can change without the essence or composition of the substance changing. For example, the state of matter of a substance (solid, liquid, gas) is a physical property. Other physical properties include: color, odor, luster, mass, volume, density, melting point and boiling point. Water is still composed of two hydrogen atoms joined to one oxygen atom no matter if is ice, water or steam.

Chemical properties are those that change as the composition of the substance changes. For example, the flammability of natural gas is dependant on the arrangement of carbon and hydrogen atoms that make it up the natural gas molecules.

Substances can undergo physical and or chemical changes. Changes in the state of matter (solid to liquid as in ice melting; liquid to gas as in water boiling) are examples of physical changes. Water still has two hydrogen atoms joined to one oxygen atom after the change. Chemical changes involve the rearrangement of the atoms into new substances. In the burning (combustion) of natural gas, the carbon and hydrogen atoms of the natural gas molecule are separated from each other and combine with oxygen gas to produce carbon dioxide and water. Some easily observable signs that a chemical reaction has occurred are: color change, temperature, and production of gas.

In this lab you will explore various physical and chemical changes.

Materials:

Baking soda (ordinary grocery store stuff); sodium bicarbonate, NaHCO3

Vinegar (ordinary grocery store stuff) a solution of acetic acid, CH3COOH

Hydrogen Peroxide (ordinary grocery store stuff), usually sold as a 3% solution, H2O2

Liquid dish soap

Yeast

Matches (wooden matches work better than the usual matchbooks made from paper/cardboard)

Drinking Glasses

Caution:

Although all of the materials listed above that are used in the following reactions are readily available at any grocery store, you need to use common sense and caution. Follow all of the product instructions. Keep them away from children and pets. Keep them out of your eyes and out of your mouth. You can dispose of the reactions by flushing them down the sink.

These reactions get foamy / fizzy, so doing them in or near a sink would be a good idea. I used a glass that was 3 inches tall and 3 inches wide. If you use a narrower glass make sure it is taller.

Instructions: After performing each step, answer the questions on the report sheet. Submit the report sheet as a file upload. Thanks!

Part 1. Baking soda + Vinegar produces... ?

Step 1. Add cup of vinegar to the glass. On your report sheet, describe the odor of the vinegar.

Step 2. Add 1 teaspoon of baking soda to the glass containing the vinegar. Describe what happens. Step 3. Light a match and hold it down into the glass. Dont get it wet and dont burn yourself. Using tweezers to hold the match or extending the reach of the match by attaching it to a straw or stick may help. Describe what happens. Step 4. After the fizzing has slowed stir the contents of the glass. Describe the odor of the vinegar / baking soda mix.

The chemical equation for the baking soda vinegar reaction is:

NaHCO3 + CH3COOH --> NaCH3COO + CO2 + H2O

(In words: baking soda and vinegar produces sodium acetate, carbon dioxide, and water)

Did a chemical reaction occur? What evidence supports your answer? Answer on the report sheet. You may discard the waste down the drain.

Part 2. Hydrogen Peroxide + dish soap produces... ?

Step 1. Add cup of Hydrogen Peroxide to the glass.

Step 2. Add several squirts of liquid dish washing soap to the glass containing the Hydrogen Peroxide. On your report sheet, describe what happens.

Step 3. Did a chemical reaction occur? What evidence supports your answer? Answer on the report sheet. You may discard the waste down the drain.

Step 4. Save the glass and its contents.

Part 3. Hydrogen Peroxide + dish soap + Yeast produces... ?

Step 1. Add a teaspoon of yeast to the glass of liquid dish washing soap and the hydrogen peroxide from Part 2. Describe what happens. Did a chemical reaction occur? What evidence supports your answer?

Step 2. This step is a little tricky. Light a match and hold it close to the foam but not touching it. Dont get it wet and dont burn yourself. Using tweezers to hold the match or extending the reach of the match by attaching it to a straw or stick may help. Describe what happens.

Based on what happens in Step 2, what gas do you think is produced in Part 3, Step 1?

Post lab Discussion:

Baking soda is classified as a base and vinegar (acetic acid) is an acid. We will cover these topics later in chapter 13. Acids and bases react to form water and dissolved salt. Initially the baking soda (NaHCO3) and acetic acid (CH3COOH) combine to form another acid, carbonic acid, H2CO3. Carbonic acid is the acid in carbonated drinks such as soda, beer and champagne. It is produced when carbon dioxide CO2 gas is dissolved in water, H2O. The carbonic acid can break apart and form carbon dioxide when you pull the tab, pop the top, or pop the cork.

The hydrogen peroxide solution is often used as an antiseptic since it is toxic to certain types of bacteria. It isnt toxic to us (or yeast) since our cells contain the enzyme catalase which decomposes the hydrogen peroxide to water and oxygen. When it is placed on wounds it fizzes as the oxygen gas is produced.

An enzyme is a protein catalyst. Catalysts are any substance that helps to speed up a chemical or biochemical reaction but arent themselves transformed in the process. One catalase enzyme can decompose several million hydrogen peroxide molecules per second!