View source for ChemCollective-Virtual-Labs/C3/Gravimetric-Analysis/English-timed


{|border=1
||'''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.
|-
|}