Welcome to this tutorial on Determination of Equilibrium Constant using Vlabs.
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.
To follow this tutorial, you should be familiar with, ChemCollective Vlabs interface.
If not for relevant tutorials please visit our website.
Here I am using, Mac OS version 10.10.5
ChemCollective virtual labs version 2.1.03 Java version 8.
Here I have opened Vlabs interface.
Click on File menu. Scroll down to Load Homework option.
Default Lab Setup dialogue-box opens.
From the list, double-click on Chemical Equilibrium. Two options appear.
Double-click on Cobalt Lab option.
Stockroom Explorer has required solutions and Problem Description.
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, equilibrium constant for cobalt chloride reaction and Effect of temperature and reactant concentration on equilibrium.
Let us define 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.
This side shows a general Equilibrium Reaction.
This is the equation for Equilibrium Constant.
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.
Equilibrium Constant changes with, Change in concentration of reactants or products and
Change in temperature.
Click on Workbench.
Double-click on Cobalt chloride experiment solutions cabinet.
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.
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 HydroCloric acid.
Click on Glassware menu. Select Erlenmeyers.
From the list click on 250 mL Erlenmeyer flask. Rename the flask as A.
From the Glassware menu, select Pipets.
From the list, click on 25 mL Pipet. From the Glassware menu, select 50 mL Buret.
Using Pipet, measure 25 mL of Cobalt chloride solution.
Click on Withdraw. Keep the flask aside.
Place the Pipet over flask A. Type 25 and Click on Pour.
Keep the Pipet aside.
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 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.
Similarly transfer another 6 mL of hydrochloric acid using Precise Transfer mode.
We have transferred 7 mL of hydrochloric acid to Flask A.
Notice the change in temperature on the thermometer.
Temperature decreases during the reaction. It means that, the reaction is endothermic.
The total volume of solution in Flask A shows 32 mL.
Observe the colour change in Flask A, colour changes to brown.
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.
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.
Again note the concentrations of Hexaaquacobalt(II)complex, chloride ions and cobalt chloride in your observation book.
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.
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.
Again note the concentrations of Hexaaquacobalt(II)complex, chloride ions and cobalt chloride at equilibrium in your observation book.
Let us see how to calculate Equilibrium Constant.
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.
Similarly, here are the values of equilibrium constant for 15, 18 and 23 mL of hydrochloric acid.
Since, temperature is constant, equilibrium constant values are almost the same.
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.
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.
Back to workbench. Keep the burette aside.
Let us increase the temperature of the reaction flask to 35 degree Celcius.
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.
Thermometer shows 35 degree Celcius.
Note the values of concentrations of Hexaaquacobalt(II)complex, Chloride ions and Cobalt Chloride.
This is the calculated value of equilibrium constant at 35 degree Celcius.
Compare it to equilibrium constant value with that at 25 degree Celcius.
Note that the value of Kc at 35 degree Celcius is greater than Kc value at 25 degree Celcius.
This is because the reaction is an endothermic reaction.
As the temperature increases rate of forward reaction increases. Hence more product is formed.
Switch to workbench, Remove the used pipette and burette from the Workbench.
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 degree Celcius.
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.
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.
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.
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.
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.
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.
The video at the following link summarizes the Spoken Tutorial project. Please download and watch it.
The Spoken Tutorial Project team, conducts workshops using spoken tutorials and gives certificates on passing online tests. For more details, please write to us.
Please post your timed queries on this forum.
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.