The reaction of an ion with standard reagents which results in a color change, precipitate or generation of a gas, is a standard method of identifying that particular ion in solution. The experiment given below is an investigation of this principle. The purpose of this laboratory is to identify eight solutions on the basis of their reactivity with other solutions. Solutions of eight compounds are to be tested and their characteristic reactions noted. Each solution contains one ion which will give a characteristic reaction by which the identity of the solution can be obtained.

Each experimental set-up contains a sample of eight solutions which are labeled A through H. An additional set of known solutions are provided. The known solutions are identical to the unknown set. They are, however, not in the same order.

No other chemical compounds have been provided and none of the samples are distilled water only. All solutions are 0.1 M. The identities of the unknowns must be verified by experimentation or documentation from sources such as your text. Check your text for the physical characteristics of the probable products of the reactions between the ions.

A confirming experiment should be done to insure the accuracy of your results. DO NOT use more than the allotted sample of solution.

CHEMICALS

All solutions 0.1 M

Silver nitrate, sodium iodide, lead nitrate, nitric acid

sodium chloride, sodium bicarbonate, iron (III) nitrate, sodium thiocyanate

Unknown solutions A - H (same as knowns)

HARDWARE

96 well microplate, distilled water for rinsing, toothpick small beaker, microtip pipettes (2)

Directions - Part 1 - Known Reactions

1. Arrange your microplate so that the numbered columns are away from you and the lettered rows are to the left.

2. Assign each of the known chemicals to a Row and a Column. For example, nitric acid may be selected for Row A and Column 1, silver nitrate may be selected for Row B and Column 2 etc.

BE SURE TO RINSE THE PIPETTE WHEN YOU SWITCH CHEMICALS!

3. Place three drops of the solution in each well in the assigned Row and Column. Repeat for each solution.

4. Use the Known Chemical Template in the Student Data Sheet below to record the assignments.

For example, if nitric acid was assigned to Row A and Column 1, write nitric acid on the sheet to indicate that assignment.

5. Mix the solutions with a single toothpick. Rinse or wipe between mixings.

6. Note any reaction in Known Chemical Template below.

7. Discard all the solutions. Rinse and dry the microplate.

Directions: Part 2 - Unknown Solutions

8. Assign each of the unknowns to a Row and a Column. For example, Unknown A, may be Row A and Column 1, Unknown B may be selected for Row B and Column 2 etc. BE SURE TO RINSE THE PIPETTE WHEN YOU SWITCH CHEMICALS!

9. Set up the Unknown Chemical Template below as you did with the Known Chemical Template in Part 1.

10. Assign the unknown solutions to the Lettered Rows and Numbered Columns as you did in Part 1.

11. Mix the solutions in the same manner as before. Wipe the toothpick before mixing the next well.

12. Note the reactions in Unknown Chemical Template.

Compare the results of the mixed unknown plate with those of the known solutions.

Student Data Sheet - THE EIGHT SOLUTION LAB

Name___________________________________ Pd _________ Date Due _____________

Known Chemical Assigned To:

Row A _______________________________ Column 1 _____________________________

Row B _______________________________ Column 2 _____________________________

Row C _______________________________ Column 3 _____________________________

Row D _______________________________ Column 4 ____________________________

Row E _______________________________ Column 5 _____________________________

Row F _______________________________ Column 6 _____________________________

Row G _______________________________ Column 7 ____________________________

Row H _______________________________ Column 8 ____________________________

Known Chemical Template

Use the legend below to characterize the reactions between chemicals:

PPT = precipitate, g = gas formed, cmplx = complex ion formed, distinct color change

W = white, R = red, B = black, etc

Unknown Chemical Assigned To:

Row A _______________________________ Column 1 _____________________________

Row B _______________________________ Column 2 _____________________________

Row C _______________________________ Column 3 _____________________________

Row D _______________________________ Column 4 ____________________________

Row E _______________________________ Column 5 _____________________________

Row F _______________________________ Column 6 _____________________________

Row G _______________________________ Column 7 ____________________________

Row H _______________________________ Column 8 ____________________________

Unknown Chemical Template (use same legend as known template)

Questions

1. Compare the reactions of the known solutions to the reactions of the unknown solutions.

2. Look at an individual precipitate or color change in the unknown combination and match it to the known combinations. Identify each unknown on the basis of the reaction comparison.

3. Identity of unknown compounds

Unknown 1____________________________ Unknown 2 ___________________________

Unknown 3____________________________ Unknown 4 ___________________________

Unknown 5____________________________ Unknown 6 ___________________________

Unknown 7____________________________ Unknown 8___________________________

This experiment caters to the students desire to "mix up all the chemicals in the lab." It is a mixture lab, but with a difference. The chemicals in the materials list were selected to give students the challenge of identification of unknowns and yet allow for the excitement of "what will happen if . . . "

Students should be motivated by telling them that a lab mix up has occurred and unlabeled bottles of chemicals have been found. The identity of all the chemicals is known, but the bottles labeled A, B, C, D etc. do not reveal the specific identity of the material. By comparing the reaction of the known chemicals to the unknowns, students will be able to correctly match the known with the unknown.

The chemicals used in this experiment are listed below. All of the solutions are 0.1 M. You may certainly change, modify or supplement the list according to your own situation. The assignment below is for reference only. You should allow students to assign them. All solutions 0.1 M: Silver nitrate, sodium iodide, lead nitrate, nitric acid, sodium chloride, sodium bicarbonate, iron (III) nitrate, sodium thiocyanate

You should provide sixteen different bottles of solution. Actually, there will be eight different solutions, two of each. One labeled with the chemical formula or name, the other with a letter designation. Students must match the chemical formula to the lettered designation.

Use the legend below to characterize the reactions between chemicals:

PPT = precipitate, g = gas formed, cmplx = complex ion formed, distinct color change

W = white, R = red, B = black, etc

Known Chemical Assigned To:

Row A ______sodium chloride__________ Column 1 _______sodium chloride___________

Row B ______sodium iodide____________ Column 2 _______sodium iodide____________

Row C ______silver nitrate____________ Column 3 _______silver nitrate_____________

Row D ______iron (III) nitrate_________ Column 4 ________iron (III) nitrate__________

Row E ______sodium bicarbonate______ Column 5 ________sodium bicarbonate_______

Row F ______nitric acid______________ Column 6 ________nitric acid______________

Row G ______lead nitrate____________ Column 7 ________lead nitrate_____________

Row H ______sodium thiocyanate______ Column 8 ________sodium thiocyanate_______

See the next page for reaction results of this combination of chemical data sheet.

Questions

1. Compare the reactions of the known solutions to the reactions of the unknown solutions.

2. Look at an individual precipitate or color change in the unknown combination and match it to the known combinations. Identify each unknown on the basis of the reaction comparison.

3. Identity of unknown compounds

Unknown 1__________________________ Unknown 2 _____________________________

Unknown 3__________________________ Unknown 4 _____________________________

Unknown 5__________________________ Unknown 6 _____________________________

Unknown 7__________________________ Unknown 8_____________________________

Notes: From Theta Technologies

If you’ve never tried a micro lab, then here’s the one for you!!

This lab is ideal for getting kids used to observing and organizing. Just give them the knows and unknows in a pipet WITHOUT directions and ask them to tell you which unknown is which known!

Higher level thinking is required.

If you liked this lab, try the other SIX collections of microlabs and kits provided by Theta Technologies!

Thanks for your time and interest. Look for our products in your favorite distributor’s catalog.

Contact us for MEANINGFUL staff development workshops.

Enjoy!!

If you use the chemicals in the list as given, and follow the directions, the plate will look like the one below. You can use the unknowns lab as an alternate assessment method and/or a final exam question.

Encourage the students to try different ideas before submitting their answers.

Known Chemical Template

1 , 2, 3, 4, 5, 6, 7, 8

A X, -, w ppt, -, -, -, w ppt, slight ,-

B -, X ,grey ppt, -, -, lt br ,yel ppt, -

C w ppt ,gr ppt , X, -, w ppt, -, -, w ppt

D -, -, -, X, ppt, -, -, red cmplx

E -, -, w ppt, ppt ,X, g, w ppt ,-

F -, lt br, -, -, g, X, -, -

G w ppt yel ppt - - w ppt - X ppt

H. - - w ppt red cmplx - - ppt X