ChemCollective-Virtual-Labs/C2/Dilutions-and-pH-Measurement/English-timed
| Time | Narration |
| 00:01 | Welcome to this tutorial on Dilutions and pH measurement. |
| 00:06 | In this tutorial, we will learn to measure: Change in pH for solutions of acid and base on dilution. |
| 00:14 | Variation in pH by common-ion effect for weak acids and bases. |
| 00:20 | To follow this tutorial, you should be familiar with, ChemCollective Vlabs interface. |
| 00:27 | If not, for relevant tutorials, please visit our website. |
| 00:32 | Here, I am using: Mac OS version 10.10.5 |
| 00:37 | ChemCollective Vlabs version 2.1.0 |
| 00:42 | Java version 8. |
| 00:45 | For this demonstration, let us dilute - 0.1 molar Hydrochloric acid to 0.01 molar Hydrochloric acid. |
| 00:54 | 0.1 molar sodium hydroxide to 0.01 molar sodium hydroxide. |
| 01:00 | For this experiment, 2 ml of 0.1 M Hydrochloric acid or sodium hydroxide is diluted to 20 ml with distilled water. |
| 01:12 | I have opened a “Virtual Chemistry labs” application window. |
| 01:18 | Stockroom explorer opens with solutions of various acids and bases.
Double-click on Strong-acids cabinet. |
| 01:29 | A list of acidic solutions with various strengths opens. |
| 01:34 | Double-click to choose 0.1 Molar Hydrocloric acid.
Click on the flask, observe the pH on the pH Meter. |
| 01:44 | Note that pH Meter reads 1.
Click on the radio button near Strong-acids cabinet, to close the list. |
| 01:54 | Next, from Stockroom explorer, double-click on Strong-bases cabinet.
A list of basic solutions with various strengths opens. |
| 02:05 | Double-click to choose point one molar Sodium Hydroxide. |
| 02:10 | Click on the flask, observe the pH on the pH Meter.
Note that pH Meter reads 13. |
| 02:19 | Click on the radio button near Strong-bases cabinet to close the list. |
| 02:25 | Double click on Distilled water icon from Stockroom explorer. |
| 02:30 | Let us now add the required apparatus to the workbench. |
| 02:35 | Click on glassware icon.
Select Graduated Cylinders. |
| 02:41 | From the sub-menu, select 10 mL Graduated Cylinder to add to the workbench. |
| 02:48 | For this experiment, we need two Graduated cylinders.
Right-click on the Graduated Cylinder. |
| 02:55 | From the context menu, select copy.
Place the cursor at a different place. |
| 03:02 | Right-click and choose Paste option from the menu. |
| 03:06 | Click on glassware icon.
Select Erlenmeyers. |
| 03:12 | From the sub-menu, select 250 mL Erlenmeyer Flask.
We require two flasks. Right-click to copy and paste. |
| 03:24 | Label the Graduated Cylinders as A and B.
Right-click on the Graduated Cylinder. |
| 03:32 | From the Context-menu, select Rename option. |
| 03:37 | A text box opens. Type A in the text box and click on Ok button. |
| 03:45 | Similarly, label the other Graduated Cylinder as B. |
| 03:51 | Similarly, label Erlenmeyer Flasks as A and B. |
| 03:59 | Place each set of apparatus at a different position on the workbench.
Use set A for acids and set B for bases. |
| 04:11 | To perform this experiment, we will dilute 2 ml of 0.1 Molar Hydrocloric acid with 18 ml of distilled water. |
| 04:22 | Drag 0.1 molar Hydrochloric acid flask over to the Graduated Cylinder A. |
| 04:30 | In the Transfer amount input bar, type 2.
Click on Pour. |
| 04:37 | Move the flask aside. |
| 04:40 | Move the Distilled water tank over Flask A.
In the Transfer amount input bar, type 18. |
| 04:48 | Click on Pour. Move the Distilled water aside. |
| 04:53 | Place the Graduated Cylinder A over Flask A. |
| 04:59 | Change the transfer mode to Realistic transfer.
Click on Pour button gradually. |
| 05:07 | Move the Graduated Cylinder A aside. |
| 05:11 | Click on Flask A, observe the pH on the pH meter.
pH meter reads 2. |
| 05:19 | Similarly, let us dilute 0.1 Molar Sodium hydroxide and measure pH. |
| 05:26 | Measure 2 mL of 0.1 Molar Sodium hydroxide in Graduated Cylinder B. |
| 05:34 | Drag 0.1 molar Sodium Hydroxide flask over to Graduated Cylinder B. |
| 05:41 | Using Tools menu, change the transfer mode to Precise transfer. |
| 05:47 | In the transfer amount input bar, type 2.
Click on Pour. |
| 05:53 | Move the flask aside. |
| 05:56 | Move the Distilled water tank over Flask B. |
| 06:00 | In the Transfer amount input bar, type 18.
Click on Pour. |
| 06:06 | Move the Distilled water aside. |
| 06:09 | Transfer 2 ml of sodium hydroxide from Graduated Cylinder B to Flask B.
Place the Graduated Cylinder B over Flask B. |
| 06:22 | Change the transfer mode to realistic transfer.
Click on Pour button gradually. |
| 06:29 | Move the Graduated Cylinder B aside. |
| 06:33 | Click on Flask B, observe the pH on the pH meter.
pH meter reads 12. |
| 06:41 | Here is a table which shows results of our experiment. |
| 06:46 | pH of 0.1 Molar Hydrocholric acid is 1. When diluted, acidity decreases.
After dilution, pH was found to be 2. |
| 06:59 | Similarly, pH of 0.1 Molar Sodium Hydroxide is 13. When diluted, alkalinity decreases. |
| 07:09 | Hence, after dilution, pH was found to be 12.
Since pH is a logarithmic scale, for every 10 times dilution pH changes by 1 unit. |
| 07:23 | Back to the workbench.
For the next experiment, load a new workbench using File menu. |
| 07:31 | Click on Workbench 2. |
| 07:34 | Let us study the variation in pH by common ion effect. |
| 07:40 | We will demonstrate this, using weak acids and weak bases. |
| 07:46 | For this demonstration , we will use two examples-
1. Ethanoic acid and its conjugate base, sodium ethanoate. 2. Ammonia and its conjugate acid, Ammonium Chloride. |
| 08:00 | Back to workbench.
Place the required chemicals from the Stockroom explorer on the workbench. |
| 08:08 | From Stockroom explorer, double-click on Weak-acids cabinet. |
| 08:14 | A list of weak acid solutions with various strengths opens.
Double-click to choose 1 molar Ethanoic acid. Close the list. |
| 08:25 | Again from Stockroom explorer, double-click on Weak-bases cabinet.
A list of weak bases with various strengths opens. |
| 08:36 | Double-click to choose 1 molar Ammonia solution.
Close the list. |
| 08:43 | Double-click on Conjugate-acids cabinet. |
| 08:47 | Double-click on 1 molar Ammonium Chloride solution.
Close the list. |
| 08:54 | Double-click on Conjugate-bases cabinet.
Double-click on 1 molar Sodium Ethanoate solution from the list. Close the list. |
| 09:05 | Next, click on new glassware icon. Select 250 ml Beaker. |
| 09:12 | We need 4 Beakers for this experiment.
Right-click on the Beaker. Using copy and paste option make 3 copies of the Beaker. |
| 09:24 | Label the beakers as A, B, C and D. |
| 09:30 | Place the Beakers A and B to one side of the workbench. |
| 09:35 | Place the Beakers C and D on other side of the workbench. |
| 09:40 | Place Ethanoic acid and its conjugate base, Sodium Ethanoate on one side. |
| 09:47 | Place Ammonia and its conjugate acid Ammonium Chloride on the other side. |
| 09:54 | Transfer 25 ml of Ethanoic acid in beakers A and B using Precise transfer mode.
Type 25 in the transfer amount input bar. |
| 10:08 | Click on pour.
Similarly, transfer 25 ml of Ethanoic acid to beaker B. |
| 10:16 | Move the flask aside. |
| 10:19 | Transfer 25 ml of Ammonia solution into beakers C and D. |
| 10:30 | Move the flask aside. |
| 10:32 | To demonstrate the effect of common ion- Transfer 25 ml of Sodium ethanoate into beaker B. |
| 10:41 | Place 1 molar Sodium ethanoate flask over beaker B. |
| 10:47 | Type 25 in the transfer amount input bar.
Click on pour. Keep the flask aside. |
| 10:55 | To check the pH of 1M Ethanoic acid present in beaker A, click on beaker A.
pH meter shows pH value of 2.38. |
| 11:10 | Click on beaker B. pH meter shows value of 4.76 . |
| 11:17 | Now transfer 25 ml of Ammonium Chloride into beaker D.
Place 1 Molar Ammonium Chloride flask over beaker D. |
| 11:29 | Type 25 in the transfer amount input bar.
Click on pour. Keep the flask aside. |
| 11:38 | To check the pH of 1molar Ammonia present in beaker C, click on beaker C. |
| 11:46 | pH meter shows pH value of 11.62. |
| 11:52 | Click on beaker D. pH meter shows pH value of 9.25.
Now, let us tabulate the results. |
| 12:03 | Due to the presence of common ion that is ethanoate ion, ionization of ethanoic acid decreases.
Hence pH value increases. |
| 12:16 | Similarly, due to the presence of ammonium ion, ionization of Ammonia decreases.
Hence pH value decreases. |
| 12:26 | Let us summarize.
In this tutorial, we have learnt to measure- Change in pH for solutions of 0.1 Molar Hydrochloric acid and 0.1 Molar Sodium Hydroxide on dilution. |
| 12:43 | Variation in pH by common-ion effect for ethanoic acid and ammonia solutions. |
| 12:51 | As an assignment: Measure change in pH for- 1 Molar and 0.01 Molar Sulphuric acid. |
| 12:59 | 1 Molar and 0.01 Molar Sodium hydroxide. |
| 13:04 | The video at the following link summarizes the Spoken Tutorial project.
Please download and watch it. |
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| 13:40 | This tutorial is contributed by Snehalatha Kaliappan and Madhuri Ganapathi from IIT-Bombay.
Thank you for joining. |
