Difference between revisions of "ChemCollective-Virtual-Labs/C3/Determination-of-Equilibrium-constant/English"

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Latest revision as of 15:59, 28 October 2020

Time Narration
Slide Number 1

Title Slide

Welcome to this tutorial on Determination of Equilibrium Constant using Vlabs.
Slide Number 2

Learning Objectives

In this tutorial, we will learn,

To determine equilibrium constant for Cobalt chloride reaction.

Observe the effect of change in temperature and concentration on equilibrium.

Slide Number 3

Pre-requisites

www.spoken-tutorial.org

To follow this tutorial, you should be familiar with,

ChemCollective Vlabs interface.

If not for relevant tutorials please visit our website.

Slide Number 4

System Requirement

Here I am using,

Mac OS version 10.10.5

ChemCollective virtual labs version 2.1.03

Java version 8.

Double click on Vlabs icon. Here I have opened Vlabs interface.
Click on File menu, Scroll down to Load Homework option.

Point to the dialog box.

Click on File menu.

Scroll down to Load Homework option.

Default Lab Setup dialog-box opens.

Click on Chemical Equilibrium.

Click on Cobalt Lab.

From the list, double-click on Chemical Equilibrium.

Two options appear.

Double-click on Cobalt Lab option.

Point to Stockroom Stockroom Explorer has required solutions and Problem Description.
Click on Problem Description.

Point to the Assignments in the problem.

Double-click on Problem Description.

Problem description states that,

we need to apply Le Chatelier's principle, for aqueous Cobalt chloride reaction.

Using the equilibrium concentration we need to find,


1. equilibrium constant for cobalt chloride reaction and

2. effect of temperature and reactant concentration on equilibrium.

Let us define chemical equilibrium.
Slide Number 5

Chemical Equilibrium

Chemical equilibrium is a state of the reversible reaction when two opposing reactions occur at the same rate.

Concentration of the reactants and products do not change with time at equilibrium.

Slide Number 6

General Equilibrium Reaction

aA+ bB ⇌ cC+dD

Kc = [C]c x [D]d/[A]a x [B]b

This side shows a general Equilibrium Reaction.

This is the equation for Equilibrium Constant.

Slide Number 7

Equilibrium Constant


[Co(H 2O)6]2+ + 4HCl + heat ⇌

CoCl4-2 + 6H2O


Kc= [ CoCl4-2]/[Co(H 2 O)6+2] x [Cl-]4

The chemical equation for this reaction is shown here.


Cobalt forms complexes with water molecules, as well as chloride ions.


A solution of Hexaaquacobalt(II)complex is pink.


When hydrochloric acid is added to the solution, the colour changes to blue.


This corresponds to the formation of Cobalt Chloride complex.

Slide Number 8

Factors Affecting Equilibrium Constant

Equilibrium Constant changes with,


1. Change in concentration of reactants or products and

2. Change in temperature.

Click on Workbench.

Double-click on Cobalt chloride experiment solutions cabinet on the Stockroom explorer.

Click on Workbench.

Double-click on Cobalt chloride experiment solutions cabinet.

Double-Click on 1M Cobalt Chloride.


Point to the added flask.

Point to the colour in the flask.

Double-Click on 1M Cobalt Chloride.


A flask with 100 mL of 1M Cobalt Chloride is added to the workbench.


Observe the colour of the solution in the flask.

Point to Solution Info panel.


Point to the colour in the flask.

Solution Info panel shows the required information.

Colour of the solution is pink due to presence of Hexaaquacobalt(II)complex.

Note the concentrations of Hexaaquacobalt(II)complex, chloride ions and Cobalt chloride in your observation book.

Double-Click on 12 M HCl. Double-Click on 12 M HCl.
Click on Glassware menu.

Select Erlenmeyers.

From the list click on 250 mL Erlenmeyer Flask.


Right-click on flask A.

From the context menu choose Rename option.

In the text box type A.

Click on OK button.

Click on Glassware menu.

Select Erlenmeyers.

From the list click on 250 mL Erlenmeyer flask.

Rename the flask as A.

Click on Pipette. From the list click on 25 mL Pipette.

Click on 50 mL Buret, click on Buret.

From the Glassware menu, select Pipets.

From the list, click on 25 mL Pipet.

From the Glassware menu, select 50 mL Buret.

Bring the pipette over to 1M CoCl2 flask.

Select Precise transfer mode.


Type 25 in the Transfer Amount input bar.

Click on Withdraw.


Drag and keep the flask aside.

Using Pipet, measure 25 mL of Cobalt chloride solution.


Click on Withdraw.


Keep the flask aside.

Place the pipette over empty 250 ml Erlenmeyer flask.

Type 25 and Click on Pour.

Place the Pipet over flask A.

Type 25 and Click on Pour.

Keep the Pipet aside.

Bring 12 M HCl flask on to 50 mL burette.

Type 50 in the transfer window. Click on Pour.

Fill the buret with 50 ml of 12 M hydrochloric acid.


Bring 12 M hydrochloric acid flask on to 50 mL buret.


Type 50 in the Transfer amount input bar.


Click on Pour.


Keep the flask aside.

Bring the burette on to flask A.

Type 1 in the transfer bar and click on pour.

Bring the buret on to flask A.


Add hydrochloric acid from the burette in 1 mL increments, using Precise Transfer mode.


Type 1 in the Transfer amount input bar and click on Pour.

Click on Pour button. Similarly transfer another 6 mL of hydrochloric acid using Precise Transfer mode.


We have transferred 7 mL of hydrochloric acid to Flask A.

Click on flask A.

Point to Solution Info Panel.

Notice the change in temperature on the thermometer.

Temperature decreases during the reaction.

It means that, the reaction is endothermic.

Point to the solution info panel. The total volume of solution in Flask A shows 32 mL.
Point to Flask A. Observe the colour change in Flask A, colour changes to brown.
Wait for few minutes till the numbers become constant.

Point to the solution info panel.

It may take a few seconds to reach equilibrium state.

Now the concentrations of the reactants and products are constant.

Note the values of the concentrations of Hexaaquacobalt(II)complex, chloride ions and cobalt chloride in your observation book.

Click on Pour.

Point to the solution info panel.

Continue the titration.

Pour 1 mL at a time into the flask.


Transfer another 8 mL of Hydrochloric acid to flask A.


Now we have transferred 15 mL of hydrochloric acid to flask A.


Total volume of liquid in flask A is 40 mL


Note the colour change in Flask A.


Please wait for the reaction to reach equilibrium condition.

Point to the concentrations in the Solution Info Panel. Again note the concentrations of Hexaaquacobalt(II)complex, chloride ions and cobalt chloride in your observation book.
Click on Pour button 3 times to add 3mL of HCl


Point to Flask A.


Point to the concentrations in the Solution Info Panel.

Similarly add another 3 ml of hydrochloric acid to flask A.

Total volume in flask A is 43 mL.


Note the colour change in flask A.


Note the concentrations in your observation book.

Click on Pour button 5 times to add 5mL of hydrochloric acid.

Point to Flask A.


Point to the concentrations in the Solution Info Panel.

Finally add 5 mL of hydrochloric acid from the buret.


Total volume in flask A is now 48 mL.


Note that we have added 23 mL of hydrochloric acid to flask A.


Colour of the solution in flask A is blue.

Point to the concentrations. Again note the concentrations of Hexaaquacobalt(II)complex, chloride ions and cobalt chloride at equilibrium in your observation book.
Cursor on Vlabs window. Let us see how to calculate Equilibrium Constant.
Slide Number 9

Calculation of Equilibrium Constant Kc.


[CoCl4-2] = 0.208 mol/L


[Co(H2O)6+2] = 0.574 mol/L


[Cl-] = 3.36 mol/L


Kc = [CoCl4-2] /[Co(H2O)6+2] [Cl-]4


Kc = 0.208/0.574 x (3.36)4 .


Kc= 2.84x10-3

Calculate Equilibrium Constant using the given formula.

Substitute the values of concentrations of cobalt chloride, Hexaaquacobalt(II)complex and chloride ions in the equation.


This is the value of equilibrium constant after pouring 7 mL of hydrochloric acid.

Slide Number 10

Equilibrium Constant


Table of Kc values.

Point to Kc values.

Similarly, here are the values of equilibrium constant for 15, 18 and 23 mL of hydrochloric acid.


Since, temperature is constant, equilibrium constant(Kc ) values are almost the same.

Cursor on workbench. Switch to workbench.

Next I will demonstrate the effect of temperature on equilibrium.


Earlier we have observed that, this reaction is endothermic.


It means, heat is absorbed during the reaction.

Slide Number 11 & 12

Le Chatelier's principle

Le Chatelier’s Principle states that,


If an equilibrium is disturbed by changing the conditions, position of equilibrium moves to counteract the change.

According to the principle, for endothermic reactions,

rate of forward reaction increases with increase in temperature.

Drag and place the burette aside. Back to workbench.

Keep the burette aside.

Right-click on flask A, from the context menu, select Thermal Properties.


In the input box, check the box for Insulated from surroundings.


Type 35 in the text box.

Let us increase the temperature of the reaction flask to 350 C.

Right-click on flask A, from the context menu, select Thermal Properties.


Input box opens.

In Set the temperature to text box, type 35.


Check the box for Insulated from surroundings.


Click on OK.

Point to thermometer. Thermometer shows 35 0 C.
Point to Solution Info panel. Note the values of concentrations of Hexaaquacobalt(II)complex, Chloride ions and Cobalt Chloride.
Slide Number 13

Effect of temperature on Kc


[CoCl4-2]= 0.447 mol/L,


[Co(H2O)6+2] = 0.074 mol/L,


[Cl-] = 5.00 mol/L

Kc=[CoCl4-2]/[Co(H2O)6+2] x [Cl-]4


Kc = 0.447 /0.074 x (5.00)4


= 9.65x10-3

This is the calculated value of equilibrium constant at 350 C.
Slide Number 14

Comparison of Equilibrium Constants


Kc at 350 C = 9.65x10-3


Kc at 250 C = 2.85x10-3

Compare it to equilibrium constant value with that at 250 C.


Note that the value of Kc at 350 C is greater than K0 value at 250C.


This is because the reaction is an endothermic reaction.


As the temperature increases rate of forward reaction increases.


Hence more product is formed.

Click on Workbench.

Right-click on pipette and buret, select Remove.

Switch to workbench,

Remove the used pipette and burette from the Workbench.

Right-click on Flask A. Uncheck the box for Insulated from surroundings. Right-click on flask A

From the context menu, select Thermal Properties.

Un-check the box for Insulated from surroundings.

Click OK.

This will bring the temperature back to 250C.

Double-Click on 6M Silver nitrate from Stockroom Explorer.


From the glassware menu, select 25 mL pipet.

Now let us remove the chloride ions from the reaction using Silver Nitrate.


Double-Click on 6M Silver nitrate from Stockroom Explorer.


From the glassware menu, select 25 mL Pipet.

Click on Withdraw


Type 5 in Transfer Amount input bar.

Click on Pour.

Withdraw 25 mL of silver nitrate(AgNO3 ) into the 25 mL Pipet.


Transfer 25 mL of silver nitrate(AgNO3) from pipet to flask A in 5 mL increments.


Type 5 in Transfer Amount input bar.

Click on Pour.

Point to the thermometer.

Point to flask A

Point to the concentrations.


Click on Solid radio button.


Point to the grams column.


[CoCl4]2- = 0.0554 mol/L


[Co(H2O)6]+2 = 0.3122 mol/L


[Cl-] = 2.808 mol/L


AgCl = 18.14 g

Note the temperature. It increases as you add silver nitrate to flask A.


Note the colour change.


It indicates the formation of Hexaaquacobalt(II)complex.


Click on Solid radio button.


Note the amount of silver chloride(AgCl) in grams column.

Slide Number 15

Chemical Equilibrium: Equations


Silver Nitrate Reaction


Cobalt chloride reaction

Silver nitrate(AgNO3) reacts with chloride(Cl-) ions in solution to form silver chloride(AgCl).


Here chloride(Cl-) ions decrease in the solution, to compensate for the deficit,


Rate of reverse reaction increases.


Cobalt chloride complex decomposes to form HexaaquaCobalt(II) complex.


This example is a proof for LeChatelier's principle.

Let us summarize.
Slide Number 16

Summary

In this tutorial, we have learnt,

To determine equilibrium constant for Cobalt chloride reaction.


Observe the effect of change in temperature and concentration on equilibrium.

Slide Number 17 & 18


Assignment


Cobalt chloride reaction

As an assignment,

Prepare a solution by adding 25 mL of Cobalt chloride solution and 23 mL of Hydrochloric acid.

Add 40 mL of water in 10 mL increments to the prepared solution

Observe the colour in the flask.

Calculate Equilibrium Constant before and after addition of water.

Slide Number 19

About Spoken Tutorial project

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Please download and watch it.

Slide Number 20

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conducts workshops using spoken tutorials and

gives certificates on passing online tests.

For more details, please write to us.

Slide Number 21

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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

Someone from our team will answer them.

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Slide Number 22

Acknowledgement

Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

More information on this mission is available at this link.

This tutorial is contributed by Snehalatha kaliappan and Madhuri Ganapathi from IIT Bombay.

Thank you for joining.

Contributors and Content Editors

Madhurig, PoojaMoolya

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