Silver Plated Bulbs

Using Tollen's test to create silver ornaments

I have used many silver mirror/Tollen's test labs. I have struggled with some and over the years I have found that this version is very reliable if the directions are followed carefully. Timing is very important too. If you choose to use glassware other than the ornaments, I will tell you that they must be very clean. Sometimes residues from other chemicals will interfere so that the silver does not adhere to the glass. As I said, I have used many versions. I have kept many of them in my paper files and on my computer. I found four different versions in my digital files and of course, none of them have author names on them. I cannot take credit for any of the details, but what I have written is a compilation of many versions. You can find kits available through the usual chemistry education vendors if you wish to go that route. If you are preparing your own silver nitrate solution, you should mix it within a couple of days of the activity. 

Have students work in with one or two partners to create one silver plated ornament bulb at a time. Helping each other is important to complete the bulb quickly. Then the group can go through the steps again until all the students have their own.

Students can follow steps #1-3 at any lab counter. It is important that they keep all solutions labeled so they can keep track of them as they move to the fume hood. 

Under the fume hood, students will add drops of concentration ammonium hydroxide per directed, add the KOH to the beaker, add more drops of ammonium hydroxide if required and then finally transfer the solution from the beaker into the ornament. Some students may opt to use a funnel for that last transfer.

Cover the opening with two pieces of parafilm and firmly press down while gently swirling. Within minutes, you will see a silver coating appear.

Be sure to follow the procedure carefully and you will have a beautiful finished product.

NOTE: Registered members of ChemEd X can find a downloadable PDF at the bottom of the post. 

Concepts: 

oxidation-reduction, Tollen's Test

Time required: 

15 minutes of prep time and 20 minutes of class time if you have multiple hoods available for students to use. I only have one hood, so I have another activity for students to complete while two groups rotate through the lab over two 60 minute class periods. 

Materials: 

Clear glass ornament bulb, test tube, flask or other clean glass container.

3 - 150 mL beakers

10 mL graduated cylinder

2 - 50 mL graduated cylinder

2 - Disposable pipettes

Parafilm (two small pieces to cover opening of ornament bulb) or stopper to fit the ornament (must be a good seal to avoid leaks)

Container to store and protect the ornament from breaking on the way home.

.25 M dextrose solution (10 mL per ornament bulb)

.8 M potassium hydroxide (KOH) (15 mL per ornament bulb)

.1 M silver nitrate solution (AgNO3) (30 mL per ornament bulb)

Concentrated ammonium hydroxide (NH4OH) (10 mL per ornament bulb)

Acetone or isopropyl alcohol (10 mL per ornament bulb)

*I offer students test tubes and tiny flasks (that were given to me by a lab that closed). I push the ornament bulbs because they are the cheapest thing that I can purchase for them to use. I purchase them every year during "after holiday sales". Although I often do this lab just before Christmas, I try not to call the product "Christmas" ornaments. The only reason I do it during that time is because I can count on having a day or two before the winter break when I will be missing many students and it is a fun, yet educational, activity.  

 
Background: 

We will create a silver coating on the inside of a glass ornament bulb by using the “silver mirror test” or “Tollen’s test”. We will mix AgNO3 (aq) with NH3 (aq) to produce a solution known as Tollen’s reagent. The Tollen’s test is used to qualitatively identify aldehydes. The reagent contains the silver diammine ion Ag(NH3)2+.  Although this ion is a very weak oxidizing agent, it will oxidize the aldehyde function group (-CHO) of dextrose, a sugar, to a carboxylate ion (-COO-).  As this oxidation occurs, silver is changed from Ag+ to solid silver which is deposited on the glass.

 

CH2OH(CHOH)4CHO   +   2[Ag(NH3)2]+   +   3OH-   →   2Ag(s) +  CH2OH(CHOH)4COO-   +   4NH3   +  2H2O

   

CH2OH(CHOH)4CHO = dextrose

[Ag(NH3)2]+   =  silver diammine ion  

 

Procedure: 

PROCEDURE (Read the procedure through before proceeding. Timing is important. You do not want to have much time elapse between steps. The NH4OH is under the hood and only two beakers are available at any given time. It is important to be patient and take turns with classmates so that no one ends up waiting between steps. Work with a partner and help each other go through the steps twice so that you each have an ornament to take home. Have all of your materials close to the hood, so that you can get to them quickly.  Once you are done adding chemicals, go elsewhere to shake the container.)

1.  Set a clean glass ornament bulb (with the metal hanger removed) on top of a 150 mL beaker.  Add 10 mL of the .25 M dextrose solution to the bulb.

2.  Measure 15 mL of .8 M potassium hydroxide (KOH) and set aside for step #5. (KOH is corrosive)

3.  Add 30 mL of .1 M silver nitrate (AgNO3) solution to a 150-mL beaker. (AgNO3 will stain skin and clothing)

4.  While stirring, add concentrated ammonium hydroxide (NH4OH) dropwise to the silver nitrate solution in the beaker until the gray black silver hydroxide (AgOH) precipitate forms.  Continue adding concentrated NH4OH dropwise with swirling until the silver diammine ionic complex (Ag(NH3)2+ forms and the solution JUST becomes clear and colorless.  

5.  Add the 15 mL of KOH measured in step #2. The silver hydroxide solid usually precipitates again, so add NH4OH dropwise with swirling until the solution clears.

6.  Pour the contents of the beaker into the glass ornament bulb. Cover the opening with two layers of parafilm (stretch to seal) or a rubber stopper. Put your finger over the parafilm (stopper) and swirl gently so the liquid contacts the entire inner surface of the glass. Continue to swirl and within 5 minutes, the entire ornament will be coated with a silver mirror surface.

7.  It is very important to pour the remaining liquid into the waste container provided by the instructor with plenty of water. Rinse the flask gently but thoroughly with water. Then rinse carefully with about 10 mL of acetone or isopropyl alcohol to help it dry quickly. You may insert the metal hanger and take it home. BE CAREFUL! I recommend putting it into a box for the trip home.

You can protect the inside of your bulb from tarnishing by coating it with a clear varnish or paint.

TEACHER NOTE: The solution remaining in the flask may form an explosive mixture upon standing. Students should dispose of excess solution immediately into a collection container provided by the instructor with copious amounts of water. The instructor should acidify the waste by adding 1M HCl until all AgCl has precipitated out. The instructor can collect the AgCl by filtering and contain for landfill disposal (or rinse and dry for other lab use). The remaining solution can be diluted further and washed down the drain with copious amounts of water. Always review current Safety Data Sheets for additional safety, handling, and disposal information.

 

 

Questions: 

1.  What is an aldehyde?  

2.  What is the specific aldehyde used in this activity?

3.  What does a “positive” Tollen’s test look like?

4.  Is the change in oxidation of the silver in this activity an oxidation or a reduction?

5.  What two reactants in the laboratory are used to produce the silver diammine ion?

6.  Look at the reactants in net ionic equation listed.  Which reactant in this activity provides the OH-?

 

Preparation: 

Mix the required solutions a day before the activity. If preparing your own solutions from the solid reagents, fresh solutions will be most reliable.

Attribution: 

As I said, I have used many versions. I have kept many of them in my paper files and on my computer. I found four different versions in my digital files and of course, none of them have author names on them. I cannot take credit for any of the details, but what I have written is a compilation of many versions. An internet search will yield many versions along with some YouTube videos. You can find another version on Flinn Scientific's website (flinnsci.com).

Safety

General Safety

Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016). Some additional information on these guidelines can be found in a Pick at ChemEd X.

Safety resources

RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies

 

NGSS

"PS1: Matter and its Interactions help students formulate an answer to the question, “How can one explain the structure, properties, and interactions of matter?” The PS1 Disciplinary Core Idea from the NRC Framework is broken down into three subideas: the structure and properties of matter, chemical reactions, and nuclear processes. Students are expected to develop understanding of the substructure of atoms and to provide more mechanistic explanations of the properties of substances. Chemical reactions, including rates of reactions and energy changes, can be understood by students at this level in terms of the collisions of molecules and the rearrangements of atoms. Students are able to use the periodic table as a tool to explain and predict the properties of elements. Using this expanded knowledge of chemical reactions, students are able to explain important biological and geophysical phenomena. Phenomena involving nuclei are also important to understand, as they explain the formation and abundance of the elements, radioactivity, the release of energy from the sun and other stars, and the generation of nuclear power. Students are also able to apply an understanding of the process of optimization in engineering design to chemical reaction systems. The crosscutting concepts of patterns, energy and matter, and stability and change are called out as organizing concepts for these disciplinary core ideas. In the PS1 performance expectations, students are expected to demonstrate proficiency in developing and using models, planning and conducting investigations, using mathematical thinking, and constructing explanations and designing solutions; and to use these practices to demonstrate understanding of the core ideas."

*More information about this category of NGSS can be found at https://www.nextgenscience.org/sites/default/files/NGSS%20DCI%20Combined....

Students who demonstrate understanding can use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.

[Clarification Statement: Examples of properties that could be predicted from patterns could include reactivity of metals, types of bonds formed, numbers of bonds formed, and reactions with oxygen.] [Assessment Boundary: Assessment is limited to main group elements. Assessment does not include quantitative understanding of ionization energy beyond relative trends.]

*More information about this category of NGSS can be found at https://www.nextgenscience.org/sites/default/files/NGSS%20DCI%20Combined....

Students who demonstrate understanding can construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

[Clarification Steatement: Examples of chemical reactions could include the reaction of sodium and chlorine, of carbon and oxygen, or of carbon and hydrogen.] [Assessment Boundary: Assessment is limited to chemical reactions involving main group elements and combustion reactions.]

*More information about this category of NGSS can be found at https://www.nextgenscience.org/sites/default/files/NGSS%20DCI%20Combined....

Students who demonstrate understanding can refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.

[Clarification Statement: Emphasis is on the application of Le Chatelier’s Principle and on refining designs of chemical reaction systems, including descriptions of the connection between changes made at the macroscopic level and what happens at the molecular level. Examples of designs could include different ways to increase product formation including adding reactants or removing products.] [Assessment Boundary: Assessment is limited to specifying the change in only one variable at a time. Assessment does not include calculating equilibrium constants and concentrations.]

*More information about this category of NGSS can be found at https://www.nextgenscience.org/sites/default/files/NGSS%20DCI%20Combined....