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# Laboratory Activities for Chapter 13

Difficulty Level: At Grade Created by: CK-12

## Chemical Reactions in Microscale

Purpose

To write balanced chemical reactions, identifying the type of reaction, and the physical characteristics that indicate a reaction has taken place.

Background

Within the five main types of chemical reactions studied in the Chemical Reactions chapter, four of these (synthesis, decomposition, single replacement, and double replacement), have subgroups of reactions that can be classified. These subgroups are known as precipitation reactions, neutralization reactions, combustion reactions, and the like. Physical changes such as: the formation of a precipitate (hence the precipitation reaction subclass), change in color, gas formation, change in temperature, tell us that a reaction has taken place. As well, within each of these reactions, whether an observable physical change has occurred or not, the Law of Conservation of mass is always maintained.

In this lab you are given seven nitrate solutions with which you are going to react seven sodium and one ammonium solutions. Planning is everything! Added to this you are only working with 10 drops of solution in total.

Materials

• \begin{align*}0.1 \ mol/L \ Cu(NO_3)_2\end{align*}
• \begin{align*}0.1 \ mol/L \ Na_2CO_3\end{align*}
• \begin{align*}0.1 \ mol/L \ Pb(NO_3)_2\end{align*}
• \begin{align*}0.1 \ mol/L \ Na_2SO_4\end{align*}
• \begin{align*}0.1 \ mol/L \ Ni(NO_3)_2\end{align*}
• \begin{align*}0.1 \ mol/L \ NaCl\end{align*}
• \begin{align*}0.1 \ mol/L \ Co(NO_3)_3\end{align*}
• \begin{align*}0.1 \ mol/L \ NaI\end{align*}
• \begin{align*}0.1 \ mol/L \ Fe(NO_3)_3\end{align*}
• \begin{align*}0.1 \ mol/L \ Na_2CrO_4\end{align*}
• \begin{align*}0.1 \ mol/L \ AgNO_3\end{align*}
• \begin{align*}0.1 \ mol/L \ Na_2Cr_2O_7\end{align*}
• \begin{align*}0.1 \ mol/L \ HNO_3\end{align*}
• \begin{align*}0.1 \ mol/L \ NaOH\end{align*}
• \begin{align*}0.1 \ mol/L \ NH_4OH\end{align*}
• \begin{align*}H_2O\end{align*}
• 24-well micro plate
• toothpicks
• beral pipettes
• 24-well micro plate (x 4)
Data Table
1 2 3 4 5 6 7 8
A
B
C
D
E
F
G

Safety

Avoid contact with the solutions. If solutions get on your skin, rinse the area thoroughly with running water.

Procedure

Part 1: Place 4 micro plates in a grid so that you have at least 8 wells in a line and 7 lines down.

Part 2: In wells A1 through to A8, add 5 drops of \begin{align*}0.1 \ mol/L \ Cu(NO_3)_2\end{align*}.

Part 3: In wells B1 though B8, add 5 drops of \begin{align*}0.1 \ mol/L \ Pb(NO_3)_2\end{align*}.

Part 4: In wells C1 though C8, add 5 drops of \begin{align*}0.1 \ mol/L \ Ni(NO_3)_2\end{align*}.

Part 5: In wells D1 though D8, add 5 drops of \begin{align*}0.1 \ mol/L \ Co(NO_3)_3\end{align*}.

Part 6: In wells E1 though E8, add 5 drops of \begin{align*}0.1 \ mol/L \ Fe(NO_3)_3\end{align*}.

Part 7: In wells F1 though F8, add 5 drops of \begin{align*}0.1 \ mol/L \ AgNO_3\end{align*}.

Part 8: In wells G1 though G8, add 5 drops of \begin{align*}0.1 \ mol/L \ HNO_3\end{align*}.

Part 9: In wells A1 through to G1, add 5 drops of \begin{align*}0.1 \ mol/L \ Na_2CO_3\end{align*}.

Part 10: In wells A2 though G2, add 5 drops of \begin{align*}0.1 \ mol/L \ Na_2SO_4\end{align*}.

Part 11: In wells A3 though G3, add 5 drops of \begin{align*}0.1 \ mol/L \ NaCl\end{align*}.

Part 12: In wells A4 though G4, add 5 drops of \begin{align*}0.1 \ mol/L \ NaI\end{align*}.

Part 13: In wells A5 though G5, add 5 drops of \begin{align*}0.1 \ mol/L \ Na_2CrO_4\end{align*}.

Part 14: In wells A6 though G6, add 5 drops of \begin{align*}0.1 \ mol/L \ Na_2Cr_2O_7\end{align*}.

Part 15: In wells A7 though G7, add 5 drops of \begin{align*}0.1 \ mol/L \ NaOH\end{align*}.

Part 16: In wells A8 though G8, add 5 drops of \begin{align*}0.1 \ mol/L \ NH_4OH\end{align*}.

Part 18: Clean Up. Empty the contents of the micro plate into the sink and rinse the plate and the sink with plenty of water. Wash your hands and the container thoroughly.

Analysis

1. Which reactions resulted in the formation of a precipitate?
2. Write balanced chemical equations for the reactions found in question 1. Can you determine based on your observations in this lab what the precipitate is likely to be? If so, indicate that in your chemical reaction.
3. What other physical changes were observed?
4. Write the balanced chemical equations for these reactions.
5. What three questions do you have as a result of doing this experiment?

Conclusion

What conclusions did you make as a result of doing this experiment?

## Chemical Reactions using Probeware

An alternate method of performing an experiment to demonstrate chemical reactions would be to use technology such as that found with the DataStudio, the GLX XPlorer, or with Vernier probeware. All three of these technology alternatives come complete with labs manuals or you can go online to http://www.pasco.com/experiments/chemistry/home.html to find other labs.

More specifically to reactions and the Law of Conservation of Mass, Pasco provides a lab such as the one entitled Classical Exothermic Reaction: Steel Wool & Vinegar at http://www.pasco.com/experiments/chemistry/october_2002/home.html

In this lab handout, students pour vinegar over steel wool and measure the change in mass and temperature as the steel wool reacts with the vinegar. Instructions for both the DataStudio 500 Interface and the XPlorerGLX are given.

## Types of Chemical Reactions

Pre-lab Questions

1. How does a decomposition reaction differ from the other types of chemical reactions?
2. In a combination reaction, what other products form in addition to any new compound?
3. Which two ions are bioaccumulative and should be used in very small quantities?
4. During which steps (give numbers) of the procedure would you expect to produce a gas?
5. What safety precaution applies when heating a test tube?

Introduction

In this experiment, you will learn to differentiate among five general types of chemical reactions. You will carry out certain representative reactions yourself, while others will be demonstrated by your teacher. From your observations you will attempt to identify the products of each reaction, and to determine the type of reaction that has taken place. The types of reactions that you will consider are the following: synthesis reactions, decomposition reactions, single replacement reactions, double replacement reactions, and combustion reactions. The majority of common chemical reactions can be classified as belonging to one of these categories. A brief description of each reaction type is provided below.

(a) Synthesis reactions are reactions in which two or more substances combine to form a single product. The reactants may be elements or compounds, but the product is always a single compound. An example of a combination reaction is a reaction of sulfur trioxide and water to form sulfuric acid.

\begin{align*}SO_{3(g)} + H_2O_{(L)} \rightarrow H_2SO_4(aq)\end{align*}

(b) Decomposition reactions are reactions in which a single substance breaks down into two or more simpler substances. There is always just a single reactant in a decomposition reaction. An example of a decomposition reaction is the breakdown of calcium carbonate upon heating.

\begin{align*}CaCO_{3(s)} + heat \rightarrow CaO_{(s)} + CO_{2(g)}\end{align*}

(c) Single replacement reactions are reactions in which an element within a compound is displaced to become a separate element. This type of reaction always has two reactants, one of which is always an element. An example of a single replacement reaction is the reaction of zinc metal with hydrochloric acid.

\begin{align*}Zn_{(s)} + 2 \ HCl_{(aq)} \rightarrow ZnCl_{2(aq)} + H_{2(g)}\end{align*}

(d) Double replacement reactions are reactions in which a positive ion from one ionic compound exchanges with the positive ion from another ionic compound. These reactions typically occur in aqueous solution and result in either the formation of a precipitate, the production of a gas, or the formation of a molecular compound such as water. An example of a double-replacement reaction is the reaction that occurs between aqueous silver nitrate and aqueous sodium chloride. A precipitate of solid silver chloride is formed in the reaction.

\begin{align*}AgNO_{3(aq)} + NaCl_{(aq)} \rightarrow AgCl_{(s)} + NaNO_{2(aq)}\end{align*}

(e) Combustion reactions are reactions in which an element or compound reacts rapidly with oxygen gas to liberate heat and light energy. Commonly, the compounds combining with oxygen in these reactions are hydrocarbons, compounds containing hydrogen and carbon. The well-known combustible fuels kerosene and gasoline, for instance, are hydrocarbon mixtures. The complete combustion of a hydrocarbon yields carbon dioxide and water as well as reaction products. If insufficient oxygen is available, combustion will not be complete and carbon monoxide and elemental carbon may be obtained as additional products in the reaction. An example of a combustion reaction is the burning of methane gas to give water (in the form of steam), carbon dioxide, heat, and light.

\begin{align*}CH_{4(g)} + 2 \ O_{2(g)} \rightarrow CO_{2(g)} + 2 \ H_2O_{(g)} + heat + light\end{align*}

Objectives:

• To observe chemical reactions in order to determine the reaction type.
• To write balanced chemical equations for each reaction.

Apparatus and Materials

• Iron filings
• safety glasses
• Copper(II) sulfate pentahydrate
• \begin{align*}2 \ \times\end{align*} small test tubes
• Magnesium, turnings
• \begin{align*}2 \ \times\end{align*} medium test tubes
• \begin{align*}0.1 \ mol/L\end{align*} copper(II) sulfate
• \begin{align*}1 \times\end{align*} large test tube
• \begin{align*}0.2 \ mol/L\end{align*} lead(II) nitrate
• \begin{align*}1 \ \times\end{align*} test tube holder
• \begin{align*}0.2 \ mol/L\end{align*} potassium iodide
• gas burner
• 3% hydrogen peroxide
• ring stand & clamp
• \begin{align*}5 \ mol/L\end{align*} hydrochloric acid
• dropper pipette
• 3% sulphuric acid (teacher demo)
• crucible tongs
• sodium bicarbonate (teacher demo)
• electrolysis apparatus (teacher demo)
• limewater (teacher demo)
• 1-holed rubber stopper (teacher demo)
• toothpicks
• 1 glass tube, \begin{align*}25 \ cm\end{align*} long bent at \begin{align*}90^\circ\end{align*} in
• matches

Procedure

1. Draw a table similar to the one below to use for collecting your observations.

Observations
Reaction Observations Reaction Type
\begin{align*}Fe\end{align*} and \begin{align*}CuSO_4\end{align*}
\begin{align*}Pb(NO_3)_2\end{align*} and \begin{align*}KI\end{align*}
\begin{align*}CuSO_4 \cdot 5H_2O\end{align*} and heat
\begin{align*}Mg\end{align*} and \begin{align*}HCl\end{align*}
\begin{align*}H_2O_2\end{align*} and heat
Electrolysis of \begin{align*}H_2O\end{align*}
\begin{align*}NaClO_2\end{align*} and heat

2. Iron metal and copper(II) sulfate solution. Fill a small test tube halfway with copper(II) sulfate solution. Add \begin{align*}2 \ g\end{align*} (about \begin{align*}\frac{1}{4}\end{align*} of a small test tube) of iron filings to the solution. Observe the reaction after \begin{align*}5 \ minutes\end{align*}. Record your observations in the observation table. Discard the solid contents of the test tube into the waste container provided. The liquid portion can be poured down the sink.

3. Lead(II) nitrate and potassium iodide solutions. Put \begin{align*}2 \ mL\end{align*} of lead(II) nitrate solution in the test tube. Add 5 to 10 drops of potassium iodide solution. Record your observations. Discard the contents of the test tube into the waste container and rinse the tube with water.

4. Action of heat on copper(II) sulfate solution. Put two or three pea-sized crystals of copper(II) sulfate pentahydrate into a large, dry test tube. Fasten a utility clamp to the upper end of the test tube. Hold the tube by the clamp so that it is almost parallel with the surface of the lab bench. CAUTION: Do not point the open mouth of the tube at yourself or anyone else. Heat the crystals gently at the bottom of the tube (where the crystals are located) in a burner flame for approximately \begin{align*}30 \ seconds\end{align*} recording your observations. When the test tube has cooled, discard its contents into the waste container provided.

5. Magnesium metal and hydrochloric acid. Fill one medium-size test tube halfway with \begin{align*}6 \ mol/L\end{align*} hydrochloric. CAUTION: Hydrochloric acid is corrosive. Place the test tube in the test tube rack. Put several pieces of magnesium turnings into the acid solution. If you observe a gas forming, test for its identity by holding a burning wood splint at the mouth of the test tube. Do not put the splint into the solution. Record your observations. Decant the liquid portion of the test tube contents into the sink; discard the solid into the waste container provided.

6. Action of heat on hydrogen peroxide. Add \begin{align*}2 \ mL\end{align*} of the 3% hydrogen peroxide solution to a medium test tube. Use a utility clamp to secure the tube to a ring stand. CAUTION: Make sure that the mouth of the tube is pointed away from you and away from everyone else. Heat the solution very gently. If you observe a gas forming, test for its identity by inserting a glowing wood splint at the mouth of the test tube. Do not put the splint into the solution. Record your observations. Rinse the contents of the test tube into the sink.

7. Action of electricity on water (Electrolysis). Water can be broken down to its component elements by passing electricity through it. This process is called electrolysis. The apparatus used for this demonstration will be explained by your teacher. Make your observations of the reaction at several intervals during a period of \begin{align*}5-10 \ minutes\end{align*}.

8. Action of heat on sodium bicarbonate. Solid sodium bicarbonate will be heated strongly in a test tube for \begin{align*}2 \ minutes\end{align*}. The gas that is given off will be tested by exposing it to a burning splint, and by bubbling it through limewater (a saturated solution of calcium hydroxide, \begin{align*}Ca(OH)_2\end{align*}). Record your observations of these tests.

Data Analysis

1. Decide which type of reaction is represented by each reaction observed in this experiment. Record your answers in your observation table.
2. Write a balanced chemical equation for each chemical reaction observed.
3. Although you did not work with any synthesis reactions in this experiment, can you describe one or give an example of one that you might have seen before or read about. Write a balanced equation for this reaction.

Results and Conclusions

1. Describe in your own words the five types of chemical reactions that were discussed in the introduction to this experiment. Explain how each type of reaction can be identified.
2. List the tests that were used in this experiment to identify gases.

Extension

1. Make a list of the reactions observed in previous experiments. Identify the types of reaction in as many cases as possible.

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