View source for ChemCollective-Virtual-Labs/C3/Determination-of-Equilibrium-constant/English

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|| '''Time''' 
|| '''Narration''' 
|- 
|| '''Slide Number 1''' 

'''Title Slide''' 
|| Welcome to this tutorial on '''Determination of Equilibrium Constant''' using '''Vlabs'''. 
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|| '''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. 
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|| '''Slide Number 3''' 

'''Pre-requisites''' 

[http://www.spoken-tutorial.org/ 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. 

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||Click on '''File''' menu, Scroll down to '''Load Homework''' option. 

Point to the dialogue box. 
||Click on '''File''' menu. 

Scroll down to '''Load Homework''' option. 

'''Default Lab Setup''' dialogue-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. 
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|| 
||Let us define chemical equilibrium. 
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|| '''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. 
 
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|| '''Slide Number 6''' 

General Equilibrium Reaction 

'''aA+ bB ⇌ cC+dD''' 

'''K<sub>c</sub> = [C]<sup>c</sup> x [D]<sup>d</sup>/[A]<sup>a</sup> x [B]<sup>b</sup>''' 
|| This side shows a general '''Equilibrium Reaction'''. 

This is the equation for '''Equilibrium Constant'''. 
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|| '''Slide Number 7''' 

'''Equilibrium Constant''' 


'''[Co(H<sub> 2</sub>O)<sub>6</sub>]<sup>2+</sup> + 4HCl + heat ⇌

'''CoCl<sub>4</sub><sup>-2</sup> + 6H<sub>2</sub>O''' 


'''K<sub>c</sub>= [ CoCl<sub>4</sub><sup>-2</sup>]/[Co(H<sub> 2</sub> O)<sub>6</sub><sup>+2</sup>] x [Cl<sup>-</sup>]<sup>4</sup>''' 
|| 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'''. 

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|| '''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 CoCl<sub>2</sub> 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. 
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|| 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 K<sub>c</sub>.''' 


[CoCl<sub>4</sub><sup>-2</sup>] <nowiki>= 0.208 mol/L</nowiki> 


[Co(H<sub>2</sub>O)<sub>6</sub><sup>+2</sup>]<sup> </sup><nowiki>= </nowiki>0.574 mol/L 


[Cl<sup>-</sup>] = 3.36 mol/L 


Kc = [CoCl<sub>4</sub><sup>-2</sup>]<sup> </sup>/[Co(H<sub>2</sub>O)<sub>6</sub><sup>+2</sup>]<sup> </sup>[Cl<sup>-</sup>]<sup>4</sup> 


'''Kc = 0.208/0.574 x (3.36)<sup>4 </sup>'''. 


'''Kc<nowiki>= </nowiki>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'''. 
 
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|| '''Slide Number 10''' 

'''Equilibrium Constant''' 


Table of K<sub>c </sub> values.

Point to K<sub>c </sub> values. 
|| Similarly, here are the values of equilibrium constant for 15, 18 and 23 mL of hydrochloric acid. 


Since, temperature is constant, equilibrium constant(K<sub>c </sub>) 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 '''35<sup>0</sup> 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 <sup>0</sup> 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 K<sub>c</sub>''' 


'''[CoCl<sub>4</sub><sup>-2</sup>]<nowiki>= 0.447 </nowiki>mol/L''', 


'''[Co(H<sub>2</sub>O)<sub>6</sub><sup>+2</sup>] <nowiki>= 0.074 </nowiki>mol/L''', 

 
'''[Cl<sup>-</sup>] <nowiki>= 5.00 </nowiki>mol/L''' 

'''K<sub>c</sub><nowiki>=</nowiki>[CoCl<sub>4</sub><sup>-2</sup>]/[Co(H<sub>2</sub>O)<sub>6</sub><sup>+2</sup>] x [Cl<sup>-</sup>]<sup>4</sup>''' 


'''K<sub>c</sub> <nowiki>= </nowiki>0.447 /0.074 x (5.00)<sup>4</sup>''' 


<nowiki>=</nowiki> 9.65x10<sup>-3</sup> 

|| This is the calculated value of equilibrium constant at '''35<sup>0</sup> C'''. 
|- 
|| '''Slide Number 14'''

'''Comparison of Equilibrium Constants''' 


'''K<sub>c</sub> at 35<sup>0</sup> C = 9.65x10<sup>-3</sup> 


'''K<sub>c</sub> at 25<sup>0 </sup>C = 2.85x10<sup>-3'''</sup> 
|| Compare it to equilibrium constant value with that at '''25<sup>0</sup> C'''. 


Note that the value of '''K<sub>c</sub>''' at '''35<sup>0 </sup> C''' is greater than '''K<sup>0</sup> value''' at '''25<sup>0</sup>C'''. 


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 25<sup>0</sup>C. 

|- 
|| 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'''(AgNO<sub>3 </sub>) into the 25 mL '''Pipet'''. 


Transfer 25 mL of '''silver nitrate(AgNO<sub>3</sub>) 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. 


'''[CoCl<sub>4</sub>]<sup>2- </sup><nowiki>= </nowiki>0.0554 mol/L''' 


'''[Co(H<sub>2</sub>O)<sub>6</sub>]<sup>+2</sup> = 0.3122 mol/L''' 


'''[Cl<sup>-]</sup> = 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(AgNO<sub>3</sub>)''' reacts with '''chloride(Cl<sup>-</sup>) ions in solution to form '''silver chloride(AgCl)'''. 


Here chloride(Cl<sup>-</sup>) 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''' 
|| The video at the following link summarizes the Spoken Tutorial project. 

Please download and watch it. 
|- 
|| '''Slide Number 20''' 

'''Spoken Tutorial workshops''' 
|| The '''Spoken Tutorial Project '''team, 

conducts workshops using spoken tutorials and 

gives certificates on passing online tests. 

For more details, please write to us. 

|- 
|| '''Slide Number 21''' 

'''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 

Someone from our team will answer them. 
|| Please post your timed queries on this forum. 
|- 
|| '''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. 
|-
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