ChemCollective-Virtual-Labs/C3/Gravimetric-Analysis/English-timed
From Script | Spoken-Tutorial
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| Time | Narration |
| 00;01 | Welcome to this spoken tutorial on Gravimetric Analysis using ChemCollective Vlabs. |
| 00:07 | In this tutorial we will determine, |
| 00:10 | The concentration of arsenic in unknown samples of contaminated water |
| 00:15 | The mass percent of arsenic in the samples |
| 00:19 | This tutorial is recorded using
Ubuntu Linux version 18.04 |
| 00:26 | ChemCollective Vlabs version 2.1.0 |
| 00:30 | Java version 11.0.8 |
| 00:34 | To follow this tutorial you should be familiar with, ChemCollective Vlabs interface. |
| 00:41 | For the prerequisite tutorials, please visit this website. |
| 00:45 | Here I have opened the Vlabs interface. |
| 00:49 | Click on File menu and select Load Homework option. |
| 00:54 | Default Lab Setup dialog box opens. |
| 00:58 | Double-Click on Quantitative Analysis folder. |
| 01:02 | You will see two problems in this folder. |
| 01:05 | Click on Gravimetric Determination of Arsenic. |
| 01:09 | Click on OK button at the bottom of the dialog-box. |
| 01:13 | Workbench 1 opens with a Stockroom Explorer on the left. |
| 01:17 | It contains required chemicals and Problem Description. |
| 01:21 | Double-click on the Problem Description. |
| 01:24 | The problem description opens in a new tab. |
| 01:28 | The aim of this experiment is to determine the amount of arsenic present in soil samples. |
| 01:34 | Read the description given here. |
| 01:37 | We have to design an experiment to determine the concentration of arsenic. |
| 01:42 | This is based on the reaction of silver ion with arsenate ion. |
| 01:47 | We have to also determine the mass percent of arsenic in the soil samples. |
| 01:53 | Close the problem description window. |
| 01:56 | Stockroom Explorer is provided with all the required chemicals. |
| 02:01 | Two samples containing unknown quantities of arsenic are provided here. |
| 02:06 | Solutions of 1 Molar silver nitrate and 0.01 Molar pure sodium arsenate are also provided. |
| 02:15 | Using gravimetric analysis we will determine the amount of arsenic present in these samples. |
| 02:22 | About Gravimetric Analysis: |
| 02:25 | It is a method which involves measurement of masses in a precipitation reaction. |
| 02:31 | This method works for a solution where either of the ions present can be precipitated. |
| 02:38 | An ion in solution is precipitated out, filtered and dried. Its mass is then related to the original ion. |
| 02:48 | Gravimetric analysis relies on stoichiometry. |
| 02:53 | Steps involved in gravimetric analysis. |
| 02:57 | Write the relevant equation for the analysis. |
| 03:01 | Find the stoichiometry of precipitated compound to the original salt in the soluble form. |
| 03:09 | Find the mass of salt in grams from moles of salt. |
| 03:13 | Grams of salt is equal to moles of the salt multiplied by Molecular weight of the salt. |
| 03:20 | Determine the mass percent of the salt. |
| 03:24 | This slide shows the reactions involved in this analysis. |
| 03:30 | Arsenate present in the soil sample reacts with sliver ion to form silver arsenate. |
| 03:38 | Silver arsenate is insoluble in water. |
| 03:44 | Gravimetric analysis relies on stoichiometry. |
| 03:50 | From this displacement reaction we know that 1 mole of sodium arsenate gives 1 mole of silver arsenate. |
| 04:00 | Let us go back to the workbench. |
| 04:04 | From the Stockroom Explorer, double-click on Sample 1 flask. |
| 04:10 | It is now added to the workbench. |
| 04:14 | Click on the Sample 1 flask. |
| 04:18 | In the solution info panel the amount of liquid present in the flask is shown as 100 ml. |
| 04:26 | The solution is clear and has no solids in it. |
| 04:30 | All the arsenic present in it is in the soluble form. |
| 04:34 | We will add an excess of silver nitrate to this sample. |
| 04:38 | This will convert all the arsenate to insoluble sliver arsenate. |
| 04:43 | Double-click on 1 Molar silver nitrate flask in the stockroom explorer . |
| 04:48 | One Molar silver nitrate is added to the workbench. |
| 04:53 | From the glassware menu, select 10 mL Pipet. |
| 04:57 | Place the Pipet in 1 Molar silver nitrate solution. |
| 05:02 | Withdraw 10 mL of silver nitrate solution. |
| 05:06 | Take the filled pipet and place it on the Sample 1 flask. |
| 05:11 | We will pour aliquots of 1ml of silver nitrate to the Sample 1 flask. |
| 05:18 | Pour 1 ml of 1 Molar silver nitrate to the flask. |
| 05:23 | On the solution info panel, click on the solid radio button if not clicked. |
| 05:29 | Observe the amount of silver arsenate precipitate. |
| 05:33 | Add 1 more ml of silver nitrate to the flask. |
| 05:37 | You will see an increase in the amount of precipitate on the solution info panel. |
| 05:42 | Add a few more ml of silver nitrate to the flask. |
| 05:46 | After a few additions you don't see any increase in the amount of precipitate. |
| 05:52 | I have added 5 ml of silver nitrate to the sample 1 flask. |
| 05:58 | Now I don't see any increase in the amount of precipitate. |
| 06:03 | This indicates that all the arsenate ions are now, in the form of insoluble silver arsenate precipitate. |
| 06:11 | In the solution info panel the amount of silver arsenate is given in grams as well as moles. |
| 06:19 | Note the amount in your observation book. |
| 06:22 | Here are the calculations: |
| 06:25 | Number of moles of silver arsenate is multiplied by molecular weight of arsenic. |
| 06:31 | This will give you the amount of arsenic in grams present in Sample 1. |
| 06:37 | Calculate the percentage of arsenic in the soil Sample 1 as shown here. |
| 06:44 | Tabulate the results of sample 1 as shown here. |
| 06:48 | Follow the same procedure and find the mass percent of arsenic in Sample 2. |
| 06:54 | I will open a new workbench. |
| 06:57 | Follow the same steps and find the number of moles of silver arsenate precipitate. |
| 07:17 | The solution info panel shows the amount of silver arsenate. |
| 07:22 | Note the amount in your observation book. |
| 07:25 | Here are the values for Sample 2. |
| 07:28 | The amount of arsenic in the unknown soil samples were found to be 59.9 milligrams and 37.4 milligrams per Kg of soil. |
| 07:39 | The World Health Organization safe limit for arsenic in drinking water is 10 micrograms per litre. |
| 07:47 | We conclude that both samples 1 and 2 have high levels of arsenic contamination. |
| 07:54 | Let us summarize
In this tutorial we have determined, the concentration of arsenic in unknown samples of contaminated water. |
| 08:04 | The mass percent of arsenic in the samples. |
| 08:08 | As an assignment
Using gravimetric analysis, design an experiment to find the amount of salt present in a bag of chips. |
| 08:17 | The video at the following link summarizes the Spoken Tutorial project.
Please download and watch it. |
| 08:25 | The spoken tutorial project team, Conducts workshops and gives certificates.
For more details, please write to us |
| 08:33 | Please post your timed queries in this forum. |
| 08:37 | Spoken Tutorial Project is funded by MHRD, Government of India. |
| 08:42 | This tutorial is contributed by Snehalatha Kaliappan and Madhuri Ganapathi from IIT-Bombay.
Thank you for watching. |
