Online Lab Experiment Qualitative Analysis A. General Background to Qualitative Analysis Experiment Qualitative analysis is a method used for identification of ions or compounds in a sample. In many cases, qualitative analysis will also involve the separation of ions or compounds in a mixture. Examples of qualitative tests would include ion precipitation reactions (solubility tests) or chemical reactivity tests. The separation of ions is easily achieved by taking advantage of their solubility properties. The goal of this lab is to use qualitative analysis to identify which cations are present in an “unknown” mixture containing one or more of the cations Ag+ , Hg2 2+ and Pb2+ (known collectively as “Group I Cations”). In a lab simulation, you will use selective precipitation, which takes advantage of the differing solubility of these ions in different conditions, to separate these ions from the mixture and then confirm their presence or absence using selective chemical reactions. In the first part of the experiment you will use a qualitative analysis scheme with known solutions containing one or more of the group I cations to show how the ions behave and can be identified. In the second part, you will perform the same procedure with an assigned “unknown” and identify which of the group I cations is present or absent. B. Specific Background to this Experiment: Separation and Identification of Group I Cations. Download the file “Qualitative Analysis Lab 364” from the assignment. This contains a portion of a paper describing “The Chemistry and Qualitative Analysis of Cations: Group Separations and Separation of Group I Cations” Read the sections titled: “Background Information”,”I, Separating Group I Cations from Group II, III and IV Cations” and “III. Group I Cations (Insoluble Chlorides)” These sections contain a specific background and explanation of the use of selective precipitation and confirmation reactions to separate and identify group I cations (Ag+ , Hg2 2+ and Pb2+) in a mixture of cations. Note that the separation procedure we will use in the online lab simulation is generally similar to that described in this paper. However, the details of the confirmations are different and are described in the online lab simulation documentation (see below). Part C of these instructions contains information on how to use the online lab simulation. Part D of these instructions describes the experiments you should carry out. Part E contains instructions on postlab questions and how to submit your lab assignment. 2 C. Instructions for Online Qualitative Analysis Simulation. 1. Go to the following website: http://web.mst.edu/~gbert/qual/qual.html This site is called “Qualitative Analysis – Cations Group I” and contains an online simulation of a qualitative analysis experiment for group I cations. It was created by Prof. Gary Bertrand of the Department of Chemistry at Missouri University of Science and Technology (https://chem.mst.edu/) and we thank him for our use of this simulation. 2. Toward the top of the page you will see heading for “Discussion”, “Flow Sheets”, “Operation” and “Check Unknown”: a) Click on “Discussion”. A new page will open that contains a description of the experiment procedures and a suggested experiment to use known solutions. It is a good idea to print this page if you can so that you can refer to it at any time. b) Click on “Operation” at any time to see instructions on how the various parts of the virtual lab simulation work. c) Click on “Flow Sheets” to see a representation of the steps in the qualitative analysis scheme used to separate and identify group I cations. d) Click on “Check Unknown” when you are ready to see if you have correctly identified the cations present and absent in your sample. 3. Watch the powerpoint presentation found in the lab assignment. In this I will show you a run through of how the online QA lab simulation works. D. Experiments To Carry Out With Online Qualitative Analysis Simulation. General: Make notes and observations as you perform procedures with the simulation. It is a good idea to note which test tube you put things into or decant from as you can’t label the tubes. Use to clear the simulation between experiments. If you get stuck, close your browser windown and reopen the simulation by going to http://web.mst.edu/~gbert/qual/qual.html Experiment 1 – Analysis of known Group I Cations Separately: For your first experiment you can carry out the “Suggested Experiment” described in the “Discussion” where you will analyze solutions containing Ag+ , Hg2 2+, and Pb2+ individually to see how they behave. Experiment 2 – Analysis of a known mixture of Group I Cations: For your second experiment, create a mixture of Ag+ , Hg2 2+ and Pb2+ by placing one drop of each in a single test tube. To do this select Ag (I) std from the “Samples” and place one drop of it in the first test tube. Repeat this to add one drop of Hg (I) std and Pb (II) std into the same test tube. Once you have this mixture, carry out the procedure described in the flow sheet (see also powerpoint presentation) to separate and confirm the presence of all three ions in this mixture. Make careful notes of what you do and note down what you observe at each step. 3 Experiment 3 – Analysis of a trial unknown: For your third experiment, select the “Trial unknown” from the samples and place 2 – 3 drops of it in the first test tube. This trial unknown contains one or more the group I cations randomly selected by the simulation. Carry out the same procedure that you did before for a mixture of known group I cations (Experiment 2). Make careful notes of what you do and note down what you observe at each step. Use your observations, along with observations you made from experiment 2, to identify whether Ag+ , Hg2 2+ and Pb2+ are present or absent in the trial unknown. When you are ready, click the “Check Unknown” and then use the appropriate buttons to select “Yes” for present and “No” for absent for each ion and then click “Check Answer” to see if you are correct. You can repeat this analysis of a trial unknown as many times as you like to practice. A new sample will be created each time you select a trial unknown. Experiment 4 – Analysis of an assigned unknown: For your fourth experiment, you will analyze an assigned unknown that contains one or more the group I cations. I will assign you a specific assigned unknown (identified by a number from 101 – 999). Instructions for this will be found in the main assignment instructions on Canvas. Make sure that you analyze the assigned unknown that I provide you. TO MAKE SURE THAT THIS EXPERIMENT WORKS CORRECTLY, IT IS IMPORTANT THAT YOU RESTART THE SIMULATION BY CLOSING THE WEBPAGE AND THEN REOPENING IT BEFORE ANALYZING THE ASSIGNED UNKNOWN. Close your webpage, reopen a new page, and go to : http://web.mst.edu/~gbert/qual/qual.html Select “Assigned Unknown” from the samples menu and type the number of your assigned unknown into the dialog box that opens. (To check that the simulation is working correctly, click “Check Unknown” and look to see if a box called “Prepare for print” appears below the options for each ion. If it does you are OK. If it says “Check answer” then it still thinks you have a trial unknown and you need to restart the simulation.). Click “Operation” or “Flow Sheet” to see the appropriate instructions again. Now you are ready to analyze your assigned unknown. Carry out the same procedure that you did for a mixture of known group I cations (Experiment 2). Make careful notes of what you do and note down what you observe at each step. Use your observations, along with observations you made from experiment 2, to identify whether Ag+ , Hg2 2+ and Pb2+ are present or absent in your assigned unknown. When you are ready click “Check Unknown”. Use the appropriate buttons to select “Yes” for present and “No” for absent for each ion. Then click “Prepare for print”. Enter your name in the dialog box that opens and click OK. A new page opens with a summary of your answer. You can print this page from your web-browser. You will need an electronic copy of this summary page for submission of your lab report. Use whatever options you have available on your PC/Mac/other platform to make a digital copy: print it and take a picture, print it and scan the print out, print to a PDF file if you have that capability, take a picture of your screen, take a screenshot…. Name the file containing the summary page of the assigned unknown using the format lastname_initial_QAlab_unknown 4
E. Postlab Questions and Submission of Lab Assignment: When you have completed the experiments in part D, including the assigned unknown, answer the postlab questions below. You can either write your answers using your MS-word editor (or equivalent), in the relevant spaces below OR print this page, write your answers by hand, and take a picture of your answers to submit on Canvas. WRITE YOUR NAME AND LAB SECTION HERE: _________________________
1. What property of group I cations like Ag+ , Hg2 2+ an Pb2+ allows them to be separated from group II and group III cations?
2. Write balanced chemical equations for the following reactions: a) AgCl (s) + NH3 (aq) b) Hg2Cl2 (s) + NH3 (aq)
3. For a solution containing at least one of the three cations involved in this experiment, answer the following questions.
a) When HCl is added to the solution, a white precipitate forms. What cation(s) may be present in the solution?
b) The tube from part a) is centrifuged, decanted and hot water is added to the precipitate. After this is centrifuged, a white solid remains. What cations(s) may be present?
c) When the decanted liquid from part b) is cooled, a white precipitate forms. What cations(s) may be present.
d) When the white solid from part b) is treated with aqueous NH3 until basic, and then centrifuged, there is no precipitate. When the decanted liquid is treated with HCl until acidic and precipitate forms. What conclusions can be made about the presence or absence of the cations in the original solution.
You may research the answers for Q 4 and Q 5 on the internet, in your textbook… 5
4. Sodium sulfide (Na2S) and sodium sulfate (Na2SO4) are both colorless, odorless solutions. Imagine you have a beaker containing a colorless, odorless solution that you know is either sodium sulfide or sodium sulfate. How could you use a chemical reaction to determine which of the compounds is in the beaker? Use chemical equations to explain your answer.
5. Sodium chloride (NaCl) and potassium chloride (KCl) are both colorless, odorless solutions. Imagine you have a beaker containing a colorless, odorless solution that you know contains one of these two solutions. What test(s) could you use to determine which solution is in the beaker.
Lab Assignment Submission: Save your answers to the postlab questions in a document with a filename based on your name e.g. lastname_initial_QAlab_postlabQ. Submit this document, along with the print out from Experiment 4 (see Part D) by uploading into the assignment on Canvas. This must be done by deadline indicated in the assignment on Canvas.
The file “Qualitative_Analysis_Lab-364.pdf” that you will read for background information can be found below:
A link to the online simulation website is present in the instructions file and can also be found here:
http://web.mst.edu/~gbert/qual/qual.html (Links to an external site.)
A powerpoint presentation containing a prelab demonstration of how to use the online simulation can be found below:
Carefully follow the instructions that describe how to perform the experiments and how to complete postlab questions.
IMPORTANT: TO FIND YOUR ASSIGNED UNKNOWN NUMBER, LOOK IN THE GRADES SECTION ON CANVAS. FIND AN ASSIGNMENT CALLED “QA Lab Unknown” AND YOU WILL SEE A SCORE REPRESENTING A NUMBER BETWEEN 101 AND 999. THIS THREE DIGIT NUMBER IS YOUR ASSIGNED UNKNOWN NUMBER.
MY UNKNOWN NUMBER IS 321
When you have completed this experiment, you will have two files. One file will your summary identifying an assigned unknown and the other will contain answers to postlab Q. Name these files as directed in the instructions and submit them using the Submit button on this page.
The deadline for this assignment is May 24th at 11:59 pm.
For the first link if it doesn’t open i provided the instruction under the link. The lab is not hard vary easy but i dont have time to do it.