GENERAL PHYSICAL SCIENCE

LAB – CHEMICAL REACTIONS

LEARNING OBJECTIVES:

Students will…

  • Distinguish between physical and chemical changes.
  • Analyze the process of a chemical reaction.
  • Adjust coefficients to balance a chemical equation.
  • Classify chemical equations as combination (synthesis), decomposition, single replacement, or double replacement.

MATERIALS

Thermometer, jar, steel wool pad, vinegar

Vocabulary

  • Coefficient – a number that multiplies a term in an equation.
  • In a chemical equation, the coefficients indicate the number of each type of molecule. For example, 6H20 means that there are six water molecules.
  • Combination– a chemical reaction in which two or more reactants form a single product.
  • Combination reactions are also called synthesis reactions.
  • For example, hydrogen (H2) combines with oxygen (O2) to form water (H2O).
  • Compound – a pure substance composed of two or more elements chemically combined.
  • A compound can be described by a chemical formula such as NaCl or H2O.
  • Decomposition – a chemical reaction in which a single substance is broken down into two or more products.
  • For example, salt (NaCl) can be decomposed into sodium (Na) and chlorine gas (Cl2).
  • Double replacement – a reaction in which two compounds exchange elements or molecules with one another.
  • For example, sodium sulfide (Na2S) and hydrochloric acid (HCl) can react to form salt (NaCl) and hydrogen sulfide (H2S).
  • Element – a pure substance that is made of one type of atom.
  • Molecule – a stable particle made of two or more atoms.
  • A water molecule (H2O) is made of two hydrogen atoms andone oxygen atom.
  • Product – a substance that is formed in a chemical reaction.
  • Reactant – a substance that takes part in a chemical reaction.
  • Single replacement – a reaction in which an element reacts with a compound to form a new compound and a different element.
  • For example, aluminum (Al) can react with hydrochloric acid (HCl) to form aluminum chloride (AlCl3) and hydrogen gas (H2).
  • Subscript – a number in a chemical formula representing the number of atoms of a particular element in one molecule of the compound.
  • For example, the subscript “2” in H2O indicates that there are two hydrogen atoms in a water molecule.

PROCEDURE #1

For each of the following, determine whether a chemical or physical change is taking place:

  1. A firecracker explodes.
  2. Chemical or physical change?
  3. Your reason:
  1. A copper penny is smashed to produce an embossed souvenir.
  2. Chemical or physical change?
  3. Your reason:
  1. Water is frozen into ice.
  2. Chemical or physical change?
  3. Your reason:
  1. An old coin tarnishes.
  2. Chemical or physical change?
  3. Your reason:

PROCEDURE #2

Chemical reactions occur every day all around us. A chemical reaction is a process where one type of substance is chemically converted to another substance. This experiment demonstrates a chemical reaction that is fairly common all around us.

  1. Put the thermometer in the jar and close the lid.
  2. Wait about 5 minutes and write down the temperature.
  3. Remove the thermometer from the jar.
  4. Soak a piece of steel wool in vinegar for one minute.
  5. Squeeze the vinegar out of the steel wool pad. Wrap the steel wool around the bulb of the thermometer.
  6. Place the thermometer and steel wool back into the jar and close the lid.
  7. Wait 5 minutes.
  8. Now take a look at the temperature.

(Make sure you use degrees Celsius and include temperatures for all the group members.)

Initial Temperature Final Temperature

Analysis

  1. Did the temperature rise or fall?
  2. Describe the appearance of the wool pad at the end of the experiment.
  3. What did the vinegar do to the wool pad?
  4. Explain what caused the temperature change.

PROCEDURE #3

This worksheet should be completed as you work through the Internet site:

If you have already enrolled in this website during lab #1, you can simply login with your username and password. If you have not already enrolled in this website, then you need to follow the directions below.

Go to the above website and click on Enroll in a Class. (Top right-hand corner)

You will then be prompted to enterthe Class Code for the class you wish to enroll in. Your Class Code is: sOLwbrjRtT

Next, you will be asked to fill in your personal information to make an account. Fill in all of the required fields and make sure you write down your username and password. We will use this site again.

Once you are in the class you will find several activities. You need to click on Launch Gizmo under the Balancing Chemical Equations.

You are now ready to do the lab.

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

The scouts are making s’mores out of toasted marshmallows, chocolate, and graham crackers.

  1. What is wrong with the image below? ______
  1. Assuming a s’more requires two graham crackers, one marshmallow, and one piece of chocolate, how many s’mores could you make with the ingredients shown? ______

Gizmo Warm-up

In a chemical reaction, reactants interact to form products. This process is summarized by a chemical equation. In the Balancing Chemical Equations Gizmo™, look at the floating molecules below the initial reaction: H2 + O2 H2O.

1.How many atoms are in a hydrogen molecule (H2)? ___

2.How many atoms are in an oxygen molecule (O2)? ____

3.How many hydrogen and oxygen atoms are in a water molecule (H2O)? ______

4.In general, what does a subscript (such as the “2” in H2) tell you about the molecule?

______

5.A chemical equation is balanced if the number of each type of atom on the left side is equal to the number of each type on the right side. Is this reaction balanced? ______

Activity A:
Balancing equations / Get the Gizmo ready:
  • Check that the Combination reaction is selected and that all coefficients are set to one. (The coefficients are the numbers in the boxes.)
/

Introduction: The equation H2 + O2 H2O is unbalanced because there are two oxygen atoms on the reactants side of the equation, and only one on the productsside of the equation. To balance the equation, you cannot change the structure of any of the molecules, but you can change the number of molecules that are used.

Question: How are chemical equations balanced?

  1. Balance: Turn on Show histograms. The equation is balanced when there are equal numbers of each type of atom represented on each side of the equation.

In the Gizmo, use the up and down arrows to adjust the numbers of hydrogen, oxygen, and water molecules until the equation is balanced. When you are done, turn on Show summary to check your answer.

Write the balanced equation here: _____ H2 + _____ O2 _____ H2O

  1. Solve: Turn off Show summary. Use the Choose reaction drop down menu to see other equations, and balance them. Check your answers and then write the balanced equations.

_____ Al + _____ HCl  _____ AlCl3 + _____ H2

_____ NaCl  _____ Na + _____ Cl2

_____ Na2S + _____ HCl  _____ NaCl + _____ H2S

  1. Practice: Balance the following chemical equations. (These equations are not in the Gizmo.)
  1. _____ Na + _____ Cl2 _____ NaCl
  1. _____ Na + _____ H2O  _____ NaOH + _____ H2
  1. _____ Mg + _____ O2 _____ MgO
  1. _____ KClO3 _____ KCl + _____ O2
  1. _____ Al + _____ CuO  _____ Al2O3 + _____ Cu
  1. _____ CaCO3 _____ CaO + _____ CO2
  1. _____ I2 + _____ Na2S2O3 _____ NaI + _____ Na2S4O6
  1. _____ Mg + _____ P4 _____ Mg3P2

Activity B:
Classifying reactions / Get the Gizmo ready:
  • Turn off Show summary and Show histograms.
/

Introduction: Chemical equations show how compounds and elements react with one another. An element is a substance consisting of one kind of atom, such as aluminum (Al) or oxygen gas (O2). A compound is a substance made of more than one kind of atom, such as water (H2O) or table salt (NaCl).

Question: How are chemical reactions classified?

  1. Match: Most chemical reactions can be classified as one of four types. Using the chemical equations in the Gizmo as a guide, match the following definitions to the type of reaction.

____ One reactant is broken down into two or more products.

____ Two or more reactants combine to form one product.

____ Two compounds react to form two different compounds.

____ A compound reacts with an element to form a new compound and a different element.

  1. Combination
  1. Decomposition
  1. Single replacement
  1. Double replacement

  1. Practice:Balance each of the chemical equations below. (Some equations may already be in balance.) In the space to the right, classify the reaction as a combination, decomposition, single replacement, or double replacement reaction.
  1. ___ AgNO3 + ___ KCl  ___ AgCl + ___ KNO3______
  1. ___ H2O + ___ SO3 ___ H2SO4______
  1. ___ KI + ___ Cl2 ___ KCl + ___ I2______
  1. ___ NaHCO3 ___ Na2CO3 + ___ H2O + ___ CO2______
  1. ___ Zn + ___ HCl  ___ ZnCl2 + ___ H2______
  1. ___ BaCl2 + ___ Na2SO4 ___ BaSO4 + ___ NaCl______
  1. ___ Ag2O  ___ Ag + ___ O2______
  1. ___ Al + ___ CuCl2 ___ AlCl3 + ___ Cu______