Silver To Black - And Back Chemistry Worksheets printable pdf download

Instructor Side

JCE Classroom Activity: #25

Silver to Black—and Back

by the Journal ’s Editorial Staff

Background

Silver and silver-plated objects react with sulfur and sulfur compounds to produce silver sulfide (Ag

S), or tarnish.

Contact with materials that contain sulfur compounds, such as hard-boiled eggs, mayonnaise, mustard, and rubber

bands can cause tarnish (1). In air, a silver object can tarnish owing to the reaction of silver with hydrogen sulfide (H

S).

This is a gas found in the air as a result of some industrial processes and the decomposition of dead plants and animals

(1). The reaction of silver with hydrogen sulfide to form tarnish is as follows:

S(g) → Ag

2Ag(s) + H

S(s) + H

(g)

The tarnish on silver can be removed with commercial silver polishes. This method usually removes the tarnish

through abrasion. As a result, each time tarnish is removed, some of the silver is lost. However, tarnish can also be

removed chemically through the reaction of aluminum with the tarnish. The aluminum is a more active metal than

silver, so it reacts with the tarnish to chemically convert the tarnish back to silver. The reaction is as follows:

S(s) + 2Al(s) → 6Ag(s) + Al

3Ag

(s)

This Activity allows students to remove tarnish from silver using the reaction of tarnish with aluminum.

Integrating the Activity into Your Curriculum

This Activity can be used with topics that range from beginning to advanced levels. These include chemical changes,

metals, electrochemistry, and redox reactions. The Activity could introduce a discussion of silver and its reactions. JCE

describes a demonstration sequence of reactions in the silver series (2). The final reaction in the sequence removes tarnish

from silver. The Activity also relates the use of chemistry to everyday objects. It can lead to parental involvement and a

discussion of household chemistry; the instructor can encourage students to share the tarnish removal method with

those at home. The topic of silver and tarnish removal can also be used in other curriculum areas, such as home econom-

ics, photography, and art conservation and restoration. The light-sensitive materials in film are silver compounds. This

Activity could be used with JCE Classroom Activity #18, “Photochemistry and Pinhole Photography” (3). PBS has

produced an episode of Scientific American Frontiers called “The Art of Science: Returned to Glory” that discusses the

restoration of art (4) that could complement this Activity.

About the Activity

This Activity uses a method of tarnish removal from silver that is less labor intensive and less expensive than the use

of commercial silver polish. An electrochemical reaction is used to convert tarnish back to silver. If only untarnished

silver items are available, students can attempt to tarnish them with sulfur compounds, as described on the Student Side.

The Activity can be used with beginning to advanced chemistry students. Instructors may wish to supplement the

questions on the Student Side with simpler or more advanced questions of their own. The Activity can be performed in

a lab or as an at-home experiment. It is an excellent candidate for use at home, since few materials are needed and all

materials used are commonly found in the home, except that some students may not have easy access to silver objects. If

the Activity is done in a lab, students could bring in their own silver objects.

Answers to Questions

S(g) → Ag

1. The reaction for tarnish formation due to contact with hydrogen sulfide is 2Ag(s) + H

S(s) + H

(g).

S(s) + 2Al(s) → 6Ag(s) + Al

2. The reaction for the tarnish removal method in the Activity is 3Ag

(s).

3. All these items contain sulfur compounds.

4. A rotten egg odor can be detected. This smell is commonly associated with sulfur compounds.

5. Possible benefits are that the Activity’s method tends to involve less work, it can be less expensive, it doesn’t involve

the loss of any silver through abrasion, and it is easier to remove tarnish from small crevices.

6. Rust is an oxide (Fe

O) and forms on the surface of objects that contain iron when the object is exposed to

air and water. Rust is usually powdery and can easily be flaked off of the object. It usually causes severe, irreversible

damage to the affected object.

Additional Activities and Demonstrations

1. Sarquis, M.; Sarquis J. Fun with Chemistry, Vol. 2; Institute for Chemical Education: Madison, WI, 1993; pp 333–337.

2. Schwenck, J. R. J. Chem. Educ. 1959, 36, 45.

3. Rigos, A. A.; Salemme, K. J. Chem. Educ. 1999, 76, 736A.

4. Scientific American Frontiers 1997–1998 Teaching Guides. The Art of Science: Returned to Glory;

44_guides/guide_804/4484_glory.html (accessed Jan 2000)

This Activity Sheet may be reproduced for use in the subscriber’s classroom.

JChemEd.chem.wisc.edu • Vol. 77 No. 3 March 2000 • Journal of Chemical Education

328A

Silver To Black - And Back Chemistry Worksheets

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