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


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||'''Visual Cue'''
||'''Narration'''
|-
|| '''Slide Number 1'''

'''Title Slide '''
||Welcome to this spoken tutorial on '''Gravimetric Analysis '''using '''ChemCollective Vlabs'''.
|-
||'''Slide Number 2 '''

'''Learning Objectives '''

||In this tutorial we will determine, 

* The concentration of '''arsenic''' in unknown samples of contaminated water
* The mass percent of '''arsenic '''in the samples 

|-
||'''Slide Number 3'''

'''System Requirement'''
||This tutorial is recorded using 

* Ubuntu Linux version 18.04
* '''ChemCollective Vlabs''' version 2.1.0
* Java version 11.0.8
|-
||'''Slide Number 4'''

'''Pre-requisites'''

'''www.spoken-tutorial.org.'''
||To follow this tutorial you should be familiar with,


'''ChemCollective Vlabs''' interface.


For the prerequisite tutorials, please visit this website.

|-
||Point to the '''Default lab setup''' window.
|| Here I have opened the '''Vlabs''' interface.

|-
||Click on '''File''', select''' Load Homework''' option.

Point to the dialog-box.
||Click on '''File '''menu and select '''Load '''

'''Homework''' option.


'''Default Lab Setup''' dialog box opens.

|-
||Double-Click on '''Quantitative Analysis '''Folder.

Click on '''Gravimetric Determination of Arsenic.'''


Click on '''OK button''' at the bottom of the dialog-box.
|| Double-Click on '''Quantitative Analysis '''folder.

You will see two problems in this folder.


Click on '''Gravimetric Determination of Arsenic.'''


Click on '''OK '''button at the bottom of the dialog-box.
|-
||Cursor on the '''workbench'''.


Point to the chemicals.
||'''Workbench 1 '''opens with a '''Stockroom Explorer''' on the left.


It contains required chemicals and''' Problem Description'''.
|-
||Double-click on '''Problem Description'''. 
||Double-click on the '''Problem Description.''' 
|-
||Point to the 1<sup>st</sup> line.
||The '''problem description '''opens in a new tab.


The aim of this experiment is to determine the amount of '''arsenic''' present in soil samples.

Read the description given here.
|-
| | Highlight the reaction of '''arsenate '''with '''silver''' ion.
||We have to design an experiment to determine the concentration of '''arsenic'''.

This is based on the reaction of silver ion with '''arsenate''' '''ion'''.
|-
| | Click on the x button on the top-right corner.
||We have to also determine the mass percent of '''arsenic''' in the soil samples.


Close the '''problem description''' window.
|-
||Point to the '''Stockroom Explorer'''.

Point to '''Sample 1''', '''Sample 2'''.


Point to 1 M '''Silver nitrate'''.


Point to 0.01 M '''Sodium arsenate'''.
||'''Stockroom Explorer''' is provided with all the required chemicals.


Two samples containing unknown quantities of '''arsenic''' are provided here.


Solutions of 1 '''Molar silver nitrate''' and 0.01 '''Molar pure sodium arsenate''' are also provided.

|-
||Cursor on the interface.
||Using '''gravimetric analysis''' we will determine the amount of '''arsenic''' present in these samples.
|-
||'''Slide Number 5'''

'''Gravimetric Analysis '''
|| About '''Gravimetric Analysis''':

1. It is a method which involves measurement of masses in a precipitation reaction.

2. This method works for a solution where either of the ions present can be precipitated.


|-
||'''Slide Number 6'''

'''Gravimetric Analysis '''

||
3. An ion in solution is precipitated out, filtered and dried. Its mass is then related to the original ion.

4. '''Gravimetric analysis''' relies on '''stoichiometry.'''

|-
||'''Slide Number 7 '''

'''Steps involved in Gravimetric Analysis '''

|| Steps involved in '''gravimetric analysis.'''

1. Write the relevant equation for the analysis.

2. Find the of precipitated compound to the original salt in the soluble form.

|-
||'''Slide Number 8'''

'''Steps involved in Gravimetric Analysis '''
||
3. Find the mass of salt in grams from moles of salt. 

Grams of salt is equal to moles of the salt multiplied by Mol wt of the salt.

4. Determine the mass percent of the salt.

|-
||'''Slide Number 9'''

'''Reactions'''

Na<sub>3</sub>AsO<sub>4</sub> (aq)+ 3AgNO<sub>3</sub> (aq) -> Ag<sub>3</sub>AsO<sub>4 </sub>(s) + 3NaNO<sub>3</sub>(aq)

AsO<sub>4</sub><sup>-3</sup>(aq) + 3 Ag<sup>+</sup>(aq) -> Ag<sub>3</sub>AsO<sub>4 </sub>(s) 
||This slide shows the reactions involved in this analysis.

'''Arsenate '''present in the soil sample reacts with sliver ion to form silver '''arsenate'''.

'''Silver arsenate''' is insoluble in water.
|-
||'''Slide Number 10'''


'''Stoichiometry'''


Na<sub>3</sub>AsO<sub>4 </sub>(aq)+ 3AgNO<sub>3</sub> (aq)-> Ag<sub>3</sub>AsO<sub>4 </sub>(s) + 3NaNO<sub>3</sub>(aq)
||'''Gravimetric analysis''' relies on '''stoichiometry'''.

From this displacement reaction we know that 1 mole of '''sodium arsenate''' gives 1 mole of '''silver arsenate.'''

|-
||From the Stockroom Explorer, 

Double-Click on '''Sample 1 '''flask.
||Let us go back to the '''workbench'''.

From the '''Stockroom Explorer''', double-click on '''Sample 1 '''flask. 

It is now added to the '''workbench'''.

|-
||Click on the '''Sample 1''' flask.

Cursor on '''Solution Info''' panel.
||Click on the '''Sample 1''' flask.


In the '''solution info''' panel the amount of liquid present in the flask is shown as 100 ml.


The solution is clear and has no solids in it.


All the arsenic present in it is in the soluble form.
|-
||Cursor on '''Sample 1''' flask.
||We will add an excess of silver nitrate to this sample.

This will convert all the '''arsenate '''to insoluble sliver arsenate. 
|-
||From the Stockroom Explorer, 

Double-click on 1 M silver nitrate flask
||Double-click on 1 Molar silver nitrate flask in the '''stockroom explorer '''.

1 Molar silver nitrate is added to the '''workbench'''.
|-
||Click on glassware menu, select Pipets.

From the submenu select 10 mL Pipet.
||From the glassware menu, select 10 mL Pipet.

|-
||Type 10 in the transfer bar at the bottom of the '''workbench'''.

Click on '''Withdraw''' button.
||Place the Pipet in 1 Molar silver nitrate solution.


'''Withdraw''' 10 mL of silver nitrate solution.


Take the filled pipet and place it on the '''Sample 1''' flask.

|-
||Type 1 in the transfer bar at the bottom of

the '''workbench'''.


Click on '''Pour''' button.

||We will pour aliquots of 1ml of silver nitrate to the '''Sample 1''' flask. 

Pour 1 ml of 1 Molar silver nitrate to the flask.

|-
|| Cursor on the '''Solution info''' panel.
||On the '''solution info''' panel, click on the solid radio button if not clicked.


Observe the amount of silver '''arsenate '''precipitate.


Add 1 more ml of silver nitrate to the flask. 
|-
||Cursor on '''Solution info''' panel.


Pour at the increments of 1 mL.
||You will see an increase in the amount of precipitate on the '''solution info''' panel.


Add a few more ml of silver nitrate to the flask.


After a few additions you don't see any increase in the amount of precipitate.


I have added 5 ml of silver nitrate to the '''sample 1''' flask.


Now I don't see any increase in the amount of precipitate.

|-
|| Cursor on the panel.
||This indicates that all the '''arsenate '''ions are now, in the form of insoluble silver '''arsenate ''' precipitate.
|-
|| In the '''solution info''' panel, in the species section, click on small black arrow.
||In the '''solution info''' panel the amount of silver '''arsenate '''is given in grams as well as moles.


Note the amount in your observation book.
|-
||'''Slide number 11'''


'''Calculations'''


Amount of Arsenic

Moles of Ag<sub>3</sub>AsO<sub>4</sub> = 0.37/462.52 = 0.000799 = 0.0008 moles


0.0008 x 74.921= 0.0599 grams of Arsenic in 1 Kg of soil.


Mass % of '''Arsenic''' in '''Sample 1''' = 0.0599 x 100/1000 = 0.00599 = 0.006 gms (60 mcg)
||Here are the calculations:


Number of moles of silver '''arsenate '''is multiplied by molecular weight of arsenic.


This will give you the amount of arsenic in grams present in '''Sample 1'''.

Calculate the percentage of arsenic in the soil '''Sample 1''' as shown here.

|-
||'''Slide Number 12'''


'''Calculation Table '''

||Tabulate the results of '''sample 1''' as shown here.
|-
|| Cursor on the '''Workbench'''.
||Follow the same procedure and find the mass percent of arsenic in '''Sample 2'''.
|-
|| Click on '''New Workbench'''.
||I will open a new '''workbench'''.


Follow the same steps and find the number of moles of silver '''arsenate '''precipitate.
|-
||In the '''solution info''' panel, in the species section, click on small black arrow.
||The '''solution info''' panel shows the amount of silver arsenate. 

Note the amount in your observation book.
|-
||'''Slide Number 13'''


'''Calculation Table '''

|| Here are the values for '''Sample 2'''.
|-
||'''Slide Number 14'''

'''Calculation Table'''
||The amount of arsenic in the unknown soil samples were found to be 59.9 milligrams and 37.4 milligrams per Kg of soil.

The World Health Organization safe limit for arsenic in drinking water is 10 micrograms per litre.

We conclude that both samples 1 and 2 have high levels of arsenic contamination. 

|-
||'''Slide Number 15'''

'''Summary '''
||Let us summarize

In this tutorial we have determined,

* the concentration of arsenic in unknown samples of contaminated water.

* the mass percent of arsenic in the samples.

|-
||'''Slide Number 16'''

'''Assignment '''

Hint: NaCl (aq) + AgNO<sub>3</sub> (aq) -> AgCl(S) + NaNO<sub>3</sub>(aq) 
||As an assignment

Using '''gravimetric analysis''',


design an experiment to find the amount of salt present in a bag of chips.

|-
||'''Slide Number 17'''

'''About Spoken Tutorial project'''
||The video at the following link summarizes the Spoken Tutorial project.

Please download and watch it.
|-
||'''Slide Number 18'''

'''Spoken Tutorial workshops'''
||The spoken tutorial project team,

Conducts workshops and gives certificates.

For more details, please write to us
|-
||'''Slide Number 19'''

'''Forum for specific questions:'''
* Do you have questions in THIS Spoken Tutorial?
* Please visit this site
* Choose the minute and second where you have the question
* Explain your question briefly
* The Spoken Tutorial project will ensure an answer
* You will have to register to ask questions

||Please post your timed queries in this forum.

|-
||'''Slide Number 20'''

'''Acknowledgement'''
||Spoken Tutorial Project is funded by MHRD, Government of India.

|-
|| 
||This tutorial is contributed by Snehalatha Kaliappan and Madhuri Ganapathi from IIT-Bombay.

Thank you for watching.
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