ChemCollective-Virtual-Labs/C3/Determination-of-Equilibrium-constant/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:01 | Welcome to this tutorial on Determination of Equilibrium Constant using Vlabs. |
| 00:08 | In this tutorial, we will learn, To determine equilibrium constant for Cobalt chloride reaction. |
| 00:15 | Observe the effect of change in temperature and concentration on equilibrium. |
| 00:22 | To follow this tutorial, you should be familiar with, ChemCollective Vlabs interface. |
| 00:29 | If not for relevant tutorials please visit our website. |
| 00:34 | Here I am using,
Mac OS version 10.10.5 |
| 00:39 | ChemCollective virtual labs version 2.1.03
Java version 8. |
| 00:48 | Here I have opened Vlabs interface. |
| 00:52 | Click on File menu. Scroll down to Load Homework option. |
| 00:57 | Default Lab Setup dialog-box opens. |
| 01:02 | From the list, double-click on Chemical Equilibrium.
Two options appear. |
| 01:10 | Double-click on Cobalt Lab option. |
| 01:14 | Stockroom Explorer has required solutions and Problem Description. |
| 01:20 | Double-click on Problem Description.
Problem description states that, we need to apply Le Chatelier's principle, for aqueous Cobalt chloride reaction. |
| 01:33 | Using the equilibrium concentration we need to find, equilibrium constant for cobalt chloride reaction and
Effect of temperature and reactant concentration on equilibrium. |
| 01:47 | Let us define chemical equilibrium. |
| 01:50 | Chemical equilibrium is a state of the reversible reaction when two opposing reactions occur at the same rate. |
| 01:59 | Concentration of the reactants and products do not change with time at equilibrium. |
| 02:06 | This side shows a general Equilibrium Reaction. |
| 02:11 | This is the equation for Equilibrium Constant. |
| 02:15 | The chemical equation for this reaction is shown here. |
| 02:20 | Cobalt forms complexes with water molecules, as well as chloride ions. |
| 02:27 | A solution of Hexaaquacobalt(II)complex is pink. |
| 02:33 | When hydrochloric acid is added to the solution, the colour changes to blue. |
| 02:39 | This corresponds to the formation of Cobalt Chloride complex. |
| 02:44 | Equilibrium Constant changes with, Change in concentration of reactants or products and |
| 02:51 | Change in temperature. |
| 02:54 | Click on Workbench. |
| 02:57 | Double-click on Cobalt chloride experiment solutions cabinet. |
| 03:03 | Double-Click on 1M Cobalt Chloride. |
| 03:07 | A flask with 100 mL of 1M Cobalt Chloride is added to the workbench.
Observe the colour of the solution in the flask. |
| 03:18 | Solution Info panel shows the required information. |
| 03:23 | Colour of the solution is pink due to presence of Hexaaquacobalt(II)complex. |
| 03:30 | Note the concentrations of Hexaaquacobalt(II)complex, chloride ions and Cobalt chloride in your observation book. |
| 03:40 | Double-Click on 12 M HydroCloric acid. |
| 03:44 | Click on Glassware menu. Select Erlenmeyers. |
| 03:50 | From the list click on 250 mL Erlenmeyer flask.
Rename the flask as A. |
| 03:59 | From the Glassware menu, select Pipets. |
| 04:03 | From the list, click on 25 mL Pipet.
From the Glassware menu, select 50 mL Buret. |
| 04:12 | Using Pipet, measure 25 mL of Cobalt chloride solution. |
| 04:18 | Click on Withdraw.
Keep the flask aside. |
| 04:23 | Place the Pipet over flask A.
Type 25 and Click on Pour. |
| 04:31 | Keep the Pipet aside. |
| 04:34 | Fill the buret with 50 ml of 12 M hydrochloric acid. |
| 04:40 | Bring 12 M hydrochloric acid flask on to 50 mL buret. |
| 04:46 | Type 50 in the Transfer amount input bar.
Click on Pour. |
| 04:52 | Keep the flask aside. |
| 04:55 | Bring the buret on to flask A. |
| 04:58 | Add hydrochloric acid from the burette in 1 mL increments, using Precise Transfer mode. |
| 05:07 | Type 1 in the Transfer amount input bar and click on Pour. |
| 05:13 | Similarly transfer another 6 mL of hydrochloric acid using Precise Transfer mode. |
| 05:22 | We have transferred 7 mL of hydrochloric acid to Flask A. |
| 05:28 | Notice the change in temperature on the thermometer. |
| 05:33 | Temperature decreases during the reaction.
It means that, the reaction is endothermic. |
| 05:41 | The total volume of solution in Flask A shows 32 mL. |
| 05:47 | Observe the colour change in Flask A, colour changes to brown. |
| 05:53 | It may take a few seconds to reach equilibrium state.
Now the concentrations of the reactants and products are constant. |
| 06:03 | Note the values of the concentrations of Hexaaquacobalt(II)complex, chloride ions and cobalt chloride in your observation book. |
| 06:14 | Continue the titration.
Pour 1 mL at a time into the flask. |
| 06:21 | Transfer another 8 mL of Hydrochloric acid to flask A. |
| 06:27 | Now we have transferred 15 mL of hydrochloric acid to flask A.
Total volume of liquid in flask A is 40 mL |
| 06:40 | Note the colour change in Flask A.
Please wait for the reaction to reach equilibrium condition. |
| 06:49 | Again note the concentrations of Hexaaquacobalt(II)complex, chloride ions and cobalt chloride in your observation book. |
| 07:00 | Similarly add another 3 ml of hydrochloric acid to flask A.
Total volume in flask A is 43 mL. |
| 07:11 | Note the colour change in flask A.
Note the concentrations in your observation book. |
| 07:19 | Finally add 5 mL of hydrochloric acid from the buret.
Total volume in flask A is now 48 mL. |
| 07:30 | Note that we have added 23 mL of hydrochloric acid to flask A. |
| 07:37 | Colour of the solution in flask A is blue. |
| 07:41 | Again note the concentrations of Hexaaquacobalt(II)complex, chloride ions and cobalt chloride at equilibrium in your observation book. |
| 07:52 | Let us see how to calculate Equilibrium Constant. |
| 07:56 | Calculate Equilibrium Constant using the given formula. |
| 08:01 | Substitute the values of concentrations of cobalt chloride, Hexaaquacobalt(II)complex and chloride ions in the equation. |
| 08:11 | This is the value of equilibrium constant after pouring 7 mL of hydrochloric acid. |
| 08:19 | Similarly, here are the values of equilibrium constant for 15, 18 and 23 mL of hydrochloric acid. |
| 08:29 | Since, temperature is constant, equilibrium constant values are almost the same. |
| 08:36 | Switch to workbench.
Next I will demonstrate the effect of temperature on equilibrium. |
| 08:45 | Earlier we have observed that, this reaction is endothermic.
It means, heat is absorbed during the reaction. |
| 08:54 | Le Chatelier’s Principle states that,
If an equilibrium is disturbed by changing the conditions, position of equilibrium moves to counteract the change. |
| 09:06 | According to the principle, for endothermic reactions, rate of forward reaction increases with increase in temperature. |
| 09:14 | Back to workbench. Keep the burette aside. |
| 09:20 | Let us increase the temperature of the reaction flask to 35 degree Celcius. |
| 09:26 | Right-click on flask A, from the context menu, select Thermal Properties.
Input box opens. |
| 09:35 | In Set the temperature to text box, type 35.
Check the box for Insulated from surroundings. Click on OK. |
| 09:46 | Thermometer shows 35 degree Celcius. |
| 09:50 | Note the values of concentrations of Hexaaquacobalt(II)complex, Chloride ions and Cobalt Chloride. |
| 09:59 | This is the calculated value of equilibrium constant at 35 degree Celcius. |
| 10:05 | Compare it to equilibrium constant value with that at 25 degree Celcius. |
| 10:12 | Note that the value of Kc at 35 degree Celcius is greater than Kc value at 25 degree Celcius. |
| 10:21 | This is because the reaction is an endothermic reaction. |
| 10:26 | As the temperature increases rate of forward reaction increases.
Hence more product is formed. |
| 10:34 | Switch to workbench,
Remove the used pipette and burette from the Workbench. |
| 10:42 | Right-click on flask A
From the context menu, select Thermal Properties. |
| 10:49 | Un-check the box for Insulated from surroundings.
Click OK. |
| 10:55 | This will bring the temperature back to 25 degree Celcius. |
| 11:00 | Now let us remove the chloride ions from the reaction using Silver Nitrate. |
| 11:07 | Double-Click on 6M Silver nitrate from Stockroom Explorer.
From the glassware menu, select 25 mL Pipet. |
| 11:18 | Withdraw 25 mL of silver nitrate(AgNO3 ) into the 25 mL Pipet. |
| 11:26 | Transfer 25 mL of silver nitrate(AgNO3) from pipet to flask A in 5 mL increments. |
| 11:34 | Type 5 in Transfer Amount input bar.
Click on Pour. |
| 11:40 | Note the temperature. It increases as you add silver nitrate to flask A. |
| 12:00 | Note the colour change. |
| 12:02 | It indicates the formation of Hexaaquacobalt(II)complex.
Click on Solid radio button. |
| 12:11 | Note the amount of silver chloride(AgCl) in grams column. |
| 12:16 | Silver nitrate(AgNO3) reacts with chloride(Cl-) ions in solution to form silver chloride(AgCl). |
| 12:23 | Here chloride(Cl-) ions decrease in the solution, to compensate for the deficit,
Rate of reverse reaction increases. |
| 12:33 | Cobalt chloride complex decomposes to form HexaaquaCobalt(II) complex.
This example is a proof for LeChatelier's principle. |
| 12:44 | Let us summarize. |
| 12:46 | In this tutorial, we have learnt, To determine equilibrium constant for Cobalt chloride reaction. |
| 12:53 | Observe the effect of change in temperature and concentration on equilibrium. |
| 12:59 | As an assignment,
Prepare a solution by adding 25 mL of Cobalt chloride solution and 23 mL of Hydrochloric acid. |
| 13:09 | Add 40 mL of water in 10 mL increments to the prepared solution
Observe the colour in the flask. |
| 13:19 | Calculate Equilibrium Constant before and after addition of water. |
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| 14:00 | This tutorial is contributed by Snehalatha kaliappan and Madhuri Ganapathi from IIT Bombay.
Thank you for joining. |
