CHEMISTRY NOW: Mystery Solution Identification (Grades 9-12) Print

Objective:

Students will be able to predict the products of a double replacement reaction and determine if a precipitate will form. Students will use their data and observations and their knowledge of solubility rules and double replacement reactions to determine the identity of several unknown solutions. Students will observe the reactions of the unknown solutions.


Introduction Notes:

CHEMISTRY NOW: Mystery Solution Identification

 

Subject Area: Chemistry                                                        

Grade Level:  High School Chemistry

Lesson Title:  Mystery Solution Identification

National Science Standards:                                                                                               

 Science as Inquiry: 9–12                                              

Physical Science Standards:

Structure and Properties of Matter: 9–12

Chemical Reactions: 9–12                                           

 

Suggested Prior Knowledge: concepts of solubility rules, precipitation reactions, double replacement reactions, net ionic equations

 

Purpose: To understand solubility rules and use this knowledge to identify unknown solutions

Key Vocabulary:  

double replacement reactiona chemical change in which two compounds exchange ions; sometimes also called double displacement reaction.

precipitatea solid that forms and settles out of a liquid mixture.

solubility—amount of a solute that will dissolve in a given quantity of solution, usually measured in grams/100 ml solution.

Objectives:      

  1. Students will be able to predict the products of a double replacement reaction and determine if a precipitate will form.
  2. Students will use their data and observations and their knowledge of solubility rules and double replacement reactions to determine the identity of several unknown solutions.
  3. Students will observe the reactions of the unknown solutions.

 

 

 

 

Materials: 

- Safety goggles

- Reaction surface (plastic sheet protector)

- Droppers or pipettes

- Several unknown solutions (number can vary depending on time available)

   (Note: all solutions should be 0.10 M)

  •   Copper (II) sulfate
  •   Iron (III) chloride
  •   Magnesium sulfate
  •   Silver nitrate
  •   Aluminum chloride
  •   Sodium phosphate
  •   Sodium carbonate
  •   Ammonium hydroxide
  •   Cobalt (II) nitrate
  •   Barium nitrate

- Unattached labels to be matched to the unknown solutions

Procedure:

1. Discuss with students the following scenario: They have been hired as new chemistry teachers at a school. When they arrive, they find the storage room in disarray. While trying to organize the chemicals and supplies, they come across several solutions in bottles without labels. They also find an identical number of labels that appear to have fallen off the unlabeled bottles. They need to determine the identity of these solutions so they can dispose of them properly (and most importantly, safely).

 

2. Discuss with students how to design a valid investigation that will allow them to use their knowledge of chemistry and solubility rules to identify the solutions and determine how to properly dispose of them. Begin with a leading question, and follow-ups:

  •  What do we know about the reactions of these possible solutions?
  •  What do we know about the properties of these possible solutions?
  •  Are any of the solutions colored?
  •  Do we know that any of the labels match colored solutions?
  •  What kind of investigation can we do to determine which of the unlabeled solutions is which?
  •  How can we determine how to safely dispose of these solutions once we can identify them?

 

3. Work with students to design a valid investigation, similar to the one outlined in this lesson, that will allow them to use the physical and chemical properties of the solutions on the labels to match each label to the correct unlabeled solution. Students should be sure their procedure is detailed and they should create appropriate data tables for their data and observations. All student procedures should be approved by the teacher before students begin any lab work.

 

 

4. A possible procedure to follow includes the following steps:

a. Begin by observing the unknown solutions. If any are colored, research which of the unknown solutions are known to be colored. Record this possible identification.

b. Predict the products for all of the possible combinations of solutions and write the balanced chemical equations for reaction.

c. Using your observations and a solubility table, identify which combinations produce precipitates.

d. Identify which, if any, of the possible precipitates are colored.

e. Using a plastic sheet protector as a reaction surface, carefully combine 1–2 drops of each solution with 1–2 drops of all of the other solutions and record your observations.

f. Use observations and data to determine which of the unknown solutions matches each of the labels.

g. Use MSDS information or the Internet to research the proper disposal method for each solution.

 

5. Other possible methods students might try include the following:

a. Students may test the pH of the solutions and try to match these to known pH values for the solutions.

b. Students may try to react the solutions with a dilute (0.10M) hydrochloric acid solution to watch for bubbling of carbonates.

c. Students may react the unknown solutions with other known solutions available in the lab.

d. Students may react the unknown solutions with various metals and use an activity series to try to identify the metal cation in the unknown solutions.

 

6. Lab safety equipment should be used, and safety protocols followed. Goggles should be worn at all times.

 

7. After the students have finished their investigations, they should be able to identify the unlabeled solutions and describe how to dispose of each correctly.

 

8. Students may present their findings to their classmates using slideshows or posters.

 

Additional Resources:

 

http://www.flinnsci.com/Sections/Safety/safety.asp

http://www.flinnsci.com/search_MSDS.asp

http://antoine.frostburg.edu/chem/senese/101/reactions/faq/predicting-products-nicl2-nh42s.shtml

http://dl.clackamas.edu/ch105-04/precipit.htm

http://chemistry.about.com/od/solutionsmixtures/a/solubility-rules.htm

http://www.ehow.com/how_6829504_disposal-lab-chemicals.html

 


Student Worksheet for Mystery Solution Identification

 

Experiment Title: ___________________Date: _______Name: _________________

 

Student Hypothesis: ___________________________________________________

 

Materials:

 

Safety goggles

 

___________________________________________________________________

 

___________________________________________________________________

 

Safety Precautions:

 

___________________________________________________________________

 

___________________________________________________________________

 

___________________________________________________________________

 

Procedure:

 

Wear safety goggles for all lab work.

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

 

Data and Observations:

 

 

 

 

 

 

 

 

 

 

Analysis of Data: 

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

 

Conclusions: 

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

 

 

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