ChemCollective-Virtual-Labs/C3/Gravimetric-Analysis/English-timed

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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.

Contributors and Content Editors

PoojaMoolya