What’s my Name?
Objectives:
In this week’s experiment you will be mixing sets of two reagents to determine if reactions have taken place. You will need to use your knowledge of the solubilities of salts and colors of their precipitates, the possibility of complex ion formations, the interactions of acids and bases and the possibility of redox reactions. You may find it helpful to review chapter four of your lecture text book, “Chemistry The Central Science, ninth Edition” by Brown, LeMay and Bursten.
Introduction:
For this experiment you will be working with another student. No teams will more than two students.
There are nine known reagents and it will be your job to mix each reagent with the other eight reagents. You will need to record in detail all of your observations for each combination of reagents. For example: what is the color of the liquid phase? Did a precipitate form? What is the color of the precipitate? Was it granular, crystalline or gelatinous? Was there formation of a gas or odor? From these observations you will note which mixtures react and which do not react.
You will then repeat the process using six unknown reagents, mixing two of them together until you have mixed each reagent with the other five unknowns. Comparing these observations along with the observations for the known reagents, you should be able to identify the six unknown reagents.
Procedure:
Note – The use of clean glassware and medicine droppers is necessary to prevent
cross contamination.
Rinsing plastic medicine dropper:
First use a clean paper towel and wipe off the tip of the dropper. Then from beaker one draw up some of the clean D.I. water into the dropper. Empty the contents of the dropper into the Erlenmeyer flask. Wipe off the tip of the dropper and draw up another dropper full of D.I. water from beaker two. Empty the contents of the dropper in the Erlenmeyer flask. Wipe off the tip of the dropper and draw up another dropper full of D.I. water from beaker three. Empty the contents of the dropper in the Erlenmeyer flask. Never add any liquid from the dropper into the three beakers. Should this happen, empty the contents of the beaker in the Erlenmeyer flask, rinse out the beaker several times with clean D.I. water and refill with clean D.I. water.
Cleaning Grid Sheet:
To clean the grid sheet, take a clean paper towel and wipe off the drops of reagents. Take a squirt bottle of alcohol and wet a clean paper towel. The alcohol will remove any making pen labels. With another dry, clean paper towel wipe off the grid sheet.
All dirty/ contaminated paper towels are to be disposed of in the solid waste container, not into the waste paper basket.
Part A. Nine Known Reagents
You will need nine clean 13 mm by 100 mm test tube and test tube rack. With a marking pen, label each of the test tubes with the one of the following:
Na2SO4
KClO3
NaBr
NH4Cl
NaOH
AgNO3
Na2S
BaCl2
KIO3
3 – Various sizes of clean beakers filled ¾ full of D.I. water. You will use these beakers to clean the plastic medicine droppers.
1 – 250 mL Erlenmeyer flask – for collection of rinse water
1 – Laminated grid sheet
2 – Clean plastic medicine droppers
Your TA will direct you to the location of the nine known reagent bottles. One member of the team will add one dropper full of the known reagents to each of the 13 x 100 mm test tubes. Make sure that you add the reagents into the correct test tubes.
The other team member will label the grid sheet using a making pen, as shown below. It is not important in what order you list the reagents. Duplicate the grid labels in your lab not book for the purpose of recording your observations.
Chem. 113-9 spot experiment*
NaOH / AgNO3 / KClO3 / NaBr / NH4Cl / Na2SO4 / BaCl2 / KIO3 / Na2SNaOH
AgNO3
KClO3
NaBr
NH4Cl
Na2SO4
BaCl2
KIO3 / Don’tDo
Na2S
*Note you will not be mixing KIO3 and Na2S
Using a clean plastic dropper, draw up one dropper full of reagent from the test tube that matches the reagent name found in the diagonal list of reagents, in the above chart, this is NaOH. Add one and only one drop of this reagent to each of the cells in row two that are to the right of the reagent name. Any excess material in the dropper can be added to the Erlenmeyer flask. Remember to rinse out this dropper.
With the other clean dropper, draw up a small amount of the reagent from the test tube that matches the name of row one – column 2, in the above chart, this is AgNO3. Add one and only one drop to the cell in row two – column 2, on top of the drop you previously put down. Rinse the dropper and move to the next cell on the right, in the above chart, this is KClO3. Continue the addition of each set of drops until you reach the end of the first row. Then, fill up the second reaction row as you did with the addition of two drops, washing out the dropper after every different chemical, until the entire grid is finished.
Go cell by cell and look to see if a reaction has taken place. Record each observation in detail in your laboratory note book, not your lab manual. To check to see if a gas has been generated, take a clean plastic medicine dropper and draw up some of the contents from a cell. Never taste anything. Never directly smell the source of any vapor or gas. Instead, first take a deep breath holding the tube well away from you, then hold the plastic medicine dropper about six inches from your nose and by means of your hand; fan air over the sample toward your nose (using this method holding the breath protects you from inhaling any vapors). Be very careful not to touch any chemical to your face or hands. Some of the reagents can severely burn your skin.
Part B. – Name the six unknown reagents.
Follow the procedure used in part A, but use the number from each of the six unknown bottles to label the various cells. Record all of your observations in your laboratory notebook.
Compare the observation from the Part B to your observations of Part A.
Lab Report is to be turned in at the beginning of next week lab.
Lab Reports will consist of the following:
Cover page:
Your Name
Title of Experiment
TA’s Name
Chem. 113
Room number
Name of your lab partner
Data Page
Copy of laboratory data from your lab notebook. Remember that at the end of class you must have your TA sign and date one page of your laboratory data for this experiment.
Identification of Unknown Page
Name each of your six unknowns.
Complete equations and net ionic equations Page
For example: The reaction of iron III nitrate with sodium hydroxide.
Complete equation:
Fe(NO3)3(aq) + 3 NaOH(aq) Fe(OH)3(s) + 3 NaNO3(aq)
Net ionic equation:
Fe 3+(aq) + 3OH –(aq) Fe(OH)3 (s)