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

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 1st 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 Na3AsO4 (aq)+ 3AgNO3 (aq) -> Ag3AsO4 (s) + 3NaNO3(aq) AsO4-3(aq) + 3 Ag+(aq) -> Ag3AsO4 (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 Na3AsO4 (aq)+ 3AgNO3 (aq)-> Ag3AsO4 (s) + 3NaNO3(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 Ag3AsO4 = 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) + AgNO3 (aq) -> AgCl(S) + NaNO3(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.
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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.

Contributors and Content Editors

Madhurig, Snehalathak