LAB 7: INTRODUCTION TO CHEMICAL REACTIONS AND EQUATIONS
- Page ID
- 505998
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)PURPOSE
The purpose of this experiment is to:
• Perform several chemical reactions and record observations.
• Balance chemical equations.
INTRODUCTION
Chemistry is defined as the study of matter and its changes. Changes in matter can be classified as physical or chemical. A physical change occurs when different forms of the same material are produced. Phase changes (such as melting or boiling) and solution formation (like the dissolution of sodium chloride in water to form saltwater) are examples of physical changes. Physical changes can be reversed without having to run a chemical reaction.
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 changes can be represented by chemical equations. Consider the conversion of hydrogen and oxygen into water:
H2 + O2 → H2O
When a chemical reaction occurs, matter cannot be created or destroyed, meaning that 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 of coefficients before 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 (2 x 2) and two oxygens (1 x 2). The right side of the equation also has four hydrogens (2 x 2) and two oxygens (2 x 1). Since this equation now has the same number of atoms on each side, it is considered balanced. For more information on balancing equations, refer to the course lectures and notes.
In this experiment, you will be recording observations from ten chemical reactions. Observations will include evidence of a reaction, such as the formation of a gas, precipitate, or odor, as well as changes in color or temperature. Then, you will be asked to balance each equation associated with the given reactions.
SAFETY PRECAUTIONS
1) Always wear chemical splash goggles while working on this experiment.
2) Gloves will be provided, should you choose to wear them. 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 belongings away from open flames. When heating test tubes, follow all directions provided by your instructor.
4) Thoroughly read and reread labels on bottles to make sure you are mixing appropriate solutions.
5) Discard chemical waste into appropriate waste containers as indicated by your instructor.
6) When you finish the experiment, thoroughly clean your work area and return the chemicals and equipment to their original locations.
EQUIPMENT* AND CHEMICALS NEEDED
• Bunsen burner with hose
• Well plate
• 600 mL beaker
• Matches or lighter or Striker
• Spatula
• Wire cutters or scissors
• Test tube rack
• Test tube holder
• 3 medium-sized test tubes
• 25 cm strip of copper wire
• Solid NaHCO3
• Solid CuSO4.5H2O
• Solid Na2CO3
• 1 M HCl
• 0.5-1 M solutions of NaCl, AgNO3, CaCl2, Na3PO4, BaCl2, Na2SO4, FeCl3, KSCN, CuSO4 and NaOH
• Solid waste container
• Inorganic waste container
* Images of equipment needed in this lab can be found in the appendix (the equipment may differ a little or be subject to changes; follow your instructors’ directions).
EXPERIMENTAL PROCEDURE
1) Gather the following equipment:
• Bunsen burner with hose
• Matches or lighter
• Test tube holder
• Test tube rack
• 25 cm strip of copper wire
• Medium size test tube containing a small scoop of solid NaHCO3 (baking soda)
• Medium size test tube containing a small scoop of solid CuSO4 . 5H2O
Note: Rinse and dry your spatula between obtaining the two solids to avoid cross-contamination.
2) Carefully light the Bunsen burner, following all instructions provided by your instructor. Hold the tip of the copper wire into the flame for 10-15 seconds. Remove the wire, note any changes in the part of the copper wire placed in the flame, and record your observations.
3) Using a test tube holder, place the tip of the test tube containing NaHCO3 into the flame for approximately 10-15 seconds, as directed by your instructor. Hold the test tube at an angle, ensuring the open end is not pointed toward you or your lab partners. Record any observations.
4) Using a test tube holder, place the tip of the test tube containing CuSO4 .5H2O into the flame for approximately 10-15 seconds, as directed by your instructor. Hold the test tube at an angle, ensuring the open end is not pointed towards you or your lab partners. Record any observations.
5) Turn off the burner. Dispose of the copper wire in the solid waste container. Pour the remaining solids in the test tubes into the inorganic waste container. Clean your work area before proceeding to the next step of the experiment.
6) Add a small scoop of solid Na2CO3 to a medium-sized test tube. Place the test tube in a test tube rack and add 10 drops of 1 M HCl. Record your observations. Pour the contents of the test tube into the inorganic waste container.
7) 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: FeCl3 and KSCN
Well 5: CuSO4 and NaOH
Well 6: FeCl3 and NaOH
Record your observations. Pour the contents of the well plate into a 600 mL beaker. Then, pour the contents of the 600 mL beaker into the inorganic waste container.
8) Thoroughly clean all glassware 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) Briefly define the following terms:
Melting:
Freezing:
Evaporation:
Condensation:
Sublimation:
Deposition:
2) Would the changes defined above be considered physical or chemical? Explain.
3) In a chemical reaction, the physical states of reactants and products are often given in parentheses (as you will see in this experiment). What do the following terms represent?
(s) :
(l) :
(g) :
(aq) :
4) What is a precipitate? Which of the notations in pre-lab question 3 can be used to represent the formation of a precipitate?
DATA AND OBSERVATIONS
For each reaction, balance the provided equation and record observations and evidence of the reaction.
Reaction 1: Copper wire and heat
Cu (s) + O2 (g) → CuO (s)
Observations:
Reaction 2: NaHCO3 and heat
NaHCO3 (s) → Na2CO3 (s) + H2O (g) + CO2 (g)
Observations:
Reaction 3: CuSO4 .5H2O and heat
CuSO4 .5H2O → CuSO4 (s) + H2O (g)
Observations:
Reaction 4: Na2CO3 and HCl
Na2CO3 (s) + HCl (aq) → NaCl (aq) + H2O (l) + CO2 (g)
Observations:
Reaction 5: NaCl and AgNO3
NaCl (aq) + AgNO3 (aq) → NaNO3 (aq) + AgCl (s)
Observations:
Reaction 6: CaCl2 and Na3PO4
CaCl2 (aq) + Na3PO4 (aq) → Ca3(PO4)2 (aq) + NaCl (aq)
Observations:
Reaction 7: BaCl2 and Na2SO4
BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + NaCl (aq)
Observations:
Reaction 8: FeCl3 and KSCN
FeCl3 (aq) + KSCN (aq) → Fe(SCN)3 (aq) + KCl (aq)
Observations:
Reaction 9: CuSO4 and NaOH
CuSO4 (aq) + NaOH (aq) → Cu(OH)2 (s) + Na2SO4 (aq)
Observations:
Reaction 10: FeCl3 and NaOH
FeCl3 (aq) + NaOH (aq) → Fe(OH)3 (s) + NaCl (aq)
Observations:
POST-LAB QUESTIONS
1) Refer to reaction 1. Explain why oxygen is a reactant when copper wire is heated.
2) Refer to reaction 4. Imagine the reaction was performed in the presence of a lit match. What would you predict to happen?
3) Refer to reaction 8. Account for the color change observed during this reaction.
4) Classify the following changes as physical or chemical.
Part A: A match is lit.
Part B: Isopropyl alcohol is dissolved in water to form a solution of rubbing alcohol.
Part C: A piece of bread begins to mold.
Part D: When sodium metal is added to water, hydrogen gas is produced.
Part E: Stream condenses on a mirror during a hot shower.
5.) Provide three examples of physical changes and three examples of chemical changes that you encounter in daily life. Write a balanced equation to describe one of the chemical changes you describe.