6: LAB 6 - CHEMICAL REACTIONS AND EQUATIONS

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Saadia Khan
Triton College

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PURPOSE

The purpose of this experiment is to:

Run several chemical reactions and record observations.
Balance chemical equations.
Predict the products of single and double replacement reactions.

INTRODUCTION

Chemical changes produce new materials. In a chemical change, atoms are rearranged as reactants (the starting materials) and are converted into products (the new materials). Chemical equations can represent chemical changes. Consider the conversion of hydrogen and oxygen into water:

H₂ + O₂ -> H₂O

In a chemical reaction, matter cannot be created or destroyed, meaning the same number and type of atoms must be shown on each side of the equation. To illustrate this, we must balance the equation by adding a whole number coefficient in front of each element or compound. We can balance the above equation as follows:

2 H₂ + O₂—-> 2 H₂O

The total number of atoms on each side of the equation can be found by multiplying the added coefficient by the given subscript. On the left side of the equation, we see four hydrogens (2x2) and two oxygens (1x2). The right side of the equation also has four hydrogens (2 × 2) and two oxygens (2 × 1). Since this equation has the same number of atoms on each side, it is balanced. Refer to the course lectures and notes for examples and detailed steps on balancing equations.

In this experiment, you will explore three reaction types: decomposition, single, and double displacement. A decomposition reaction occurs when one reactant forms two or more products. An example would be the conversion of sodium azide into sodium metal and nitrogen gas, as shown below:

2 NaN₃ (s) —-> 2 Na (s) + 3 N₂ (g)

In a single displacement reaction, one element replaces another in a compound. These reactions often run in aqueous solutions. Consider the reaction of magnesium metal with aluminum chloride:

3 Mg (s) + 2 AlCl₃ (aq) —-> 3 MgCl₂ (aq) + 2 Al (s)

In this reaction, magnesium replaces aluminum with aluminum chloride.

Like single displacement reactions, double displacement reactions also occur in aqueous solutions, and cations and anions exchange places according to the following generic equation:

AX + BY —-> AY + BX

In many cases, when two aqueous solutions are mixed, a solid, known as a precipitate, forms, as shown by the reaction between sodium bromide and silver nitrate:

NaBr (aq) + AgNO₃ (aq) —-> NaNO₃ (aq) + AgBr (s)

To predict the products of a double displacement reaction, write the four ions present in the solution (in this case, Na⁺, Br^-, Ag⁺, and NO₃^-) and pair opposite ions together, writing the formula for the ionic compound. One quick way to identify a precipitate (if it forms) is by looking at the two cations. The precipitate typically forms from the heavier metal cation. In this reaction, silver is heavier than sodium. A more formal method for determining whether a precipitate will form when two aqueous solutions are mixed is by examining a list of solubility guidelines provided in the course textbook.

SAFETY PRECAUTIONS

1. Always wear chemical splash goggles while working on this experiment.

2. Wearing gloves, especially when working with silver nitrate, is advisable, as it can cause skin stains. Be sure to thoroughly wash your hands after completing this experiment.

3. Exercise caution when working with Bunsen burners. Keep notebooks, purses, books, and other equipment away from open flames. Follow all directions provided by your instructor when heating test tubes.

4. Thoroughly read and reread the bottles' labels to ensure you mix the appropriate solutions.

5. Dispose of chemical waste in the designated waste containers, as instructed by your instructor.

6. Thoroughly clean your work area and return chemicals and equipment to their designated places after the experiment.

EQUIPMENT* AND CHEMICALS NEEDED

Equipment and Chemicals
EQUIPMENT	EQUIPMENT	CHEMICALS	CHEMICALS
10 mL graduated cylinder	5 Medium-sized Test Tubes, Test Tube Rack, and a Test Tube Holder	Solid Magnesium and Zinc	0.5 M OR 1.0 M solutions of CuSO₄, AgNO₃, NaCl, CaCl₂, Na₃PO₄, BaCl₂, Na₂SO₄, NaOH, FeCl₃
Bunsen burner with hose	Well plate	Solid CuSO₄_.5H₂O	1 M HCl
Matches, lighter, or Striker.	Spatula	copper wire	Solid NaHCO₃
Wire cutters or scissors	600 mL beaker	Solid Waste Container	Inorganic Waste Container

* Images of equipment needed in this lab can be found in the appendix (the equipment may differ or be subject to changes; follow your instructor’s directions).

EXPERIMENTAL PROCEDURE

Part A: Decomposition Reactions

Gather the following equipment and assemble the Bunsen burner.
Bunsen burner with the hose, matches or lighter, test tube holder, test tube rack, and two medium-sized test tubes.
Take two medium-sized test tubes. Add a small scoop of solid NaHCO₃ (baking soda) to the first medium-sized test tube and a small scoop of solid CuSO₄ · 5H₂O to the second medium-sized test tube. Note: Rinse and dry your spatula between obtaining the two solids to avoid cross-contamination.
Using a test tube holder, place the tip of the test tube containing NaHCO₃ into the flame for a few minutes. Hold the test tube at an angle, ensuring the open end is not pointed towards you or your lab partners. Record any observations.
Using a test tube holder, place the tip of the test tube containing CuSO₄ · 5H₂O into the flame for a few minutes. Hold the test tube at an angle, ensuring the open end is not pointed towards you or your lab partners. Record any observations.
Turn off the burner. After the remaining solids in the test tubes have cooled, pour them into the inorganic waste container. Clean your work area and all glassware before proceeding to the next step of the experiment.

Part B: Single Displacement Reactions

Take five test tubes, add a small scoop of Mg (s), Zn (s), and Cu (s) to three separate test tubes, a small scoop of Zn (s) to the fourth test tube, and a small piece of copper wire to the fifth test tube. Secure the test tubes in the test tube rack.
Add approximately 2.0 mL of 1.0 M HCl into the FIRST THREE test tubes ONLY and record your observations.
Into the fourth test tube with a small scoop of Zn (s), add enough CuSO₄ solution to cover the Zn (s) completely. Record your initial observation and then your observations after 15 minutes and 30 minutes. (While waiting, you can work on Part C)
Using a small piece of copper wire, add enough AgNO3 solution to completely cover the Cu (s) in the fifth test tube. Record your initial observation and then your observations after 15 and 30 minutes.
Leave the test tubes in the rack, and after the 30-minute observation, pour out the contents of the test tubes into a 600 mL beaker. Using forceps, remove any unreacted metal and place it on a paper towel. Place the solution into the inorganic waste container and dry the unreacted metal in the metal waste. Clean and dry the test tubes.

Part C: Double Displacement Reactions

1. Obtain a well plate, and add 5-10 drops of each solution to the following wells:

Well 1: NaCl and AgNO₃

Well 2: CaCl₂ and Na₃PO₄

Well 3: BaCl₂ and Na₂SO₄

Well 4: CuSO₄ and Na₃PO₄

Well 5: CuSO₄ and NaOH

Well 6: FeCl₃ and NaOH

Well 7: CaCl₂ and Na₂SO₄

Well 8: FeCl₃ and Na₂SO₄

2. Record your observations in the data table, part C. Pour the contents of the well plate into a 600.0 mL beaker. The contents of the 600 mL beaker should then be poured into the inorganic waste container.

3. Thoroughly clean all glassware and the well plate with soap and water. Return all equipment and chemicals to their appropriate places. Clean your work area before leaving the lab.

PRE-LAB QUESTIONS

Name: ____________________________________

1. Provide three examples of evidence showing that a chemical reaction has occurred.

2. Balance the following chemical equations:

PCl₅ (g) —-> PCl₃ (g) + Cl₂(g)

Al (s) + HCl (aq) —-> AlCl₃ (aq) + H₂ (g)

Na₂S (aq) + BaCl₂ (aq) —-> NaCl (aq) + BaS (aq)

3. Using a list of solubility guidelines, predict whether the following compounds will be soluble or insoluble in water.

Pb(NO₃)₂:

PbCl₂:

SrS:

Fe(OH)₃:

Na₂SO₄:

AlPO₄:

CuCO₃:

KI:

4. Predict the products and their physical states for each reaction. (Hint: Refer to a table of solubility guidelines to determine whether a precipitate would form.). Then, balance the overall equation.

Al (s) + CuCl₂ (aq) —->

NiCl₂ (aq) + KOH (aq) —->

Ca(C₂H₃O₂)₂ (aq) + Na₂SO₄ (aq) —->

DATA AND OBSERVATIONS

Name: _Lab Partner(s): ______

Part A: Decomposition Reactions

For each of the reactions, balance the provided equation. Record all observations and evidence of reaction.

Part A: Decomposition Reactions
Reactions	Balance the provided equation. Record all observations and evidence of reaction.
Reaction 1: NaHCO₃ and Heat	_NaHCO₃ (s) → _Na₂CO₃ (s) +_H₂O (g) +_CO₂ (g)
Observations:
Evidence of Reaction:
Reaction 2: CuSO₄ · 5H₂O and Heat	_CuSO₄.5H₂O → _CuSO₄ (s) + _H₂O (g)
Observations:
Evidence of Reaction:

Part B: Single Displacement Reactions

Predict the products' physical states for each reaction, and balance the equation. If no reaction occurs, write NR. Record all observations and evidence of reaction.

Part B: Single Displacement Reactions
Reactions	Complete Balanced Equation- Observations and Evidence of Reaction.
Reaction 1: Mg and HCl	_ Mg (s) + _ HCl (aq) →
Observations:
Evidence of Reaction:
Reaction 2: Zn and HCl	Zn (s) + HCl (aq) →
Observations:
Evidence of Reaction:
Reaction 3: Cu and HCl	Cu (s) + HCl (aq) →
Observations:
Evidence of Reaction:
Reaction 4: Zn and CuSO₄	Zn (s) + CuSO₄ (aq) →
Observations:
Evidence of Reaction:
Reaction 5: Cu and AgNO₃	Cu (s) + AgNO₃ (aq) →
Observations:
Evidence of Reaction:

Part C: Double Displacement Reactions

Predict the physical states of the products for each reaction and balance the equation. If no reaction occurs, write NR. Record all observations and evidence of response.

Part C: Double Displacement Reactions
Reactions	Complete Balanced Equation - Observations and Evidence of Reaction.
Reaction 1: NaCl and AgNO₃	NaCl (aq) + AgNO₃ (aq) →
Observations:
Evidence of Reaction:
Reaction 2: CaCl₂ and Na₃PO₄	CaCl₂ (aq) + Na₃PO₄ (aq) →
Observations:
Evidence of Reaction:
Reaction 3: BaCl₂ and Na₂SO₄	BaCl₂ (aq) + Na₂SO₄ (aq) →
Observations:
Evidence of Reaction:
Reaction 4: CuSO₄ and Na₃PO₄	CuSO₄ (aq) + Na₃PO₄ (aq) →
Observations:
Evidence of Reaction:
Reaction 5: CuSO₄ and NaOH	CuSO₄ (aq) + NaOH (aq) →
Observations:
Evidence of Reaction:
Reaction 6: FeCl₃ and NaOH	FeCl₃ (aq) + NaOH (aq) →
Observations:
Evidence of Reaction:
Reaction 7: CaCl₂ and Na₂SO₄	CaCl₂ (aq) + Na₂SO₄ (aq) →
Observations:
Evidence of Reaction:
Reaction 8: FeCl₃ and Na₂SO₄	FeCl₃ (aq) + Na₂SO₄ (aq) →
Observations:
Evidence of Reaction:

POST LAB QUESTIONS

Another type of reaction is the redox (or oxidation-reduction). Which of the three reactions (decomposition, single displacement, or double displacement) explored during this lab can also be classified as redox reactions? Explain.
An activity series can be used to predict whether a single displacement reaction will occur as written. Any metal on the list can react when placed into solutions containing ions listed below it in the activity series. Access an activity series (from either the course textbook or by doing a Google search) and briefly explain how it summarizes the results of the reactions observed in part B.
For part C, did any reactions not produce a precipitate? If yes, which one(s)? Would these still be classified as chemical changes? Explain.

Please click here to access just the Pre-Lab, Data Tables, and Post-Lab in Word or PDF format. Complete them and upload according to your instructor's instructions.

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SAFETY PRECAUTIONS

Part A: Decomposition Reactions

Part B: Single Displacement Reactions

Part C: Double Displacement Reactions

PURPOSE

INTRODUCTION

SAFETY PRECAUTIONS

EQUIPMENT* AND CHEMICALS NEEDED

EXPERIMENTAL PROCEDURE

Part A: Decomposition Reactions

Part B: Single Displacement Reactions

Part C: Double Displacement Reactions

PRE-LAB QUESTIONS

Name: ____________________________________

DATA AND OBSERVATIONS

Name: _________________________Lab Partner(s): ______________________________

Part A: Decomposition Reactions

Part B: Single Displacement Reactions

Part C: Double Displacement Reactions

POST LAB QUESTIONS

Name: _Lab Partner(s): ______