ChemCollective-Virtual-Labs/C2/Buffer-Solutions/English-timed

Time	Narration
00:01	Welcome to this spoken tutorial on Buffer Solutions.
00:05	In this tutorial we will learn, to prepare 0.5 M Acetate buffer of pH 3.6 and test the buffering action with small amounts of acid and base.
00:18	To follow this tutorial you should be familiar with, ChemCollective Vlabs interface.
00:25	If not, for relevant tutorials please visit our website.
00:30	Here I am using Mac OS version 10.10.5 ChemCollective Vlabs version 2.1.0
00:39	Java version 8.0.
00:41	Here I have opened Virtual Chemistry Labs application window.
00:46	Click on File menu, and select Load homework option. Default Lab setup dialog box opens.
00:55	Double-click on Acids and Bases folder. Click on Buffer Creation Problem.
01:02	The required chemicals for this experiment are provided in the Stockroom Explorer. Let me demonstrate how to make Acetate buffer solution.
01:12	A buffer solution, is composed of a weak acid or weak base and its conjugate salt.
01:19	Its pH changes very little when a small amount of acid or base is added to it.
01:26	Henderson–Hasselbalch equation is useful for estimating the pH of a buffer solution.
01:33	Please refer to the excellent tutorial on buffers at the following link.
01:38	To prepare Acetate buffer of a particular pH, Acetic acid and Sodium acetate are mixed in various proportions.
01:46	To prepare 50 ml of pH 3.6 Acetate buffer- We have to mix 46.3 ml of 0.1 M Acetic acid and 3.7 ml of Sodium acetate.
02:01	Back to the Workbench. Let us retrieve the chemicals and apparatus required for this experiment.
02:09	From the Stockroom Explorer click on water, 1M Sodium acetate and 1M Acetic acid.
02:18	From Glassware cabinet retrieve, 250 ml Erlenmeyer flask, 50 ml graduated cylinder.
02:28	Make the duplicates of all the apparatus. Rename graduated cylinders as G1 and G2.
02:39	Rename Erlenmeyer flasks as A1 and A2.
02:46	Let us prepare 0.5 M Acetic acid by diluting 1 M Acetic acid.
02:53	Measure 50 ml of Acetic acid in the graduated cylinder G1.
03:02	Pour the contents of the graduated cylinder G1 into Erlenmeyer flask A1.
03:11	Measure 50 ml of water using the same graduated cylinder.
03:18	Pour water into Erlenmeyer flask A1.
03:24	Click on flask A1 and note the pH. It shows a pH of '2.53.
03:32	Similarly prepare 0.5 M Sodium acetate solution.
03:38	Measure 50 ml of 1M Sodium acetate solution in graduated cylinder G2.
03:47	Transfer this solution into Erlenmeyer flask A2.
03:54	Measure 50 ml of water using the same graduated cylinder.
04:01	Pour water from graduated cylinder into Erlenmeyer flask A2.
04:08	Click on flask A2, note the pH. It shows a pH of 9.23.
04:16	We now have 0.5 M of Acetic acid and 0.5 M Sodium acetate solutions.
04:23	Retrieve a 250 ml beaker from the glassware cabinet.
04:28	Transfer 46.3 ml of 0.5 M Acetic acid into the beaker.
04:35	Bring flask A1 over to the beaker.
04:39	Type 46.3 in the Transfer amount input bar. Click on Pour.
04:46	Transfer 3.7ml of 0.5 M Sodium Acetate into the beaker.
04:53	Bring flask A2 over to the beaker.
04:56	Type 3.7 in the Transfer amount input bar. Click on Pour.
05:04	Click on the beaker, check the pH in the PH Meter. pH is shown as 3.66.
05:13	We now have an acetate buffer solution of pH 3.66.
05:19	Rename the beaker with buffer solution as Acetate buffer.
05:25	Remove the used Erlenmeyer flasks and Graduates cylinders from the Workbench.
05:32	To test the buffering action, select water, hydrochloric acid(HCl) and 1M sodium hydroxide(NaOH) from Stockroom Explorer.
05:43	We will have to dilute, 1M hydrochloric acid(HCl) and 1M sodium hydroxide(NaOH) to 0.1 M hydrochloric acid(HCl) and 0.1 M sodium hydroxide(NaOH).
05:56	Retrieve two sets of- 10 ml graduated cylinders 250 ml beakers
06:06	Disposable pipettes from the glassware cabinet.
06:12	Rename graduated cylinders as G1 and G2.
06:18	Rename Beakers as A and B
06:22	Rename Disposable pipette as P1 and P2.
06:28	Measure 9 ml of water using graduated cylinder G1 Pour it in 250 ml Beaker A.
06:39	Add 1 ml of 1M HCl to Beaker A using disposable pipette P1.
06:51	0.1 M of hydrochloric acid(HCl) is ready for use.
06:57	Similarly dilute 1M sodium hydroxide(NaOH) with water to prepare 0.1M sodium hydroxide(NaOH).
07:08	Prepare 0.1 M sodium hydroxide(NaOH) in beaker B, similarly as before.
07:18	Diluted acid has a pH of 1. Diluted base has a pH of 13.
07:25	Let us add a small amount of acid to check the buffering action.
07:30	Place the disposable pipette over the flask A.
07:34	Withdraw 0.2 mL of HCl from flask A.
07:40	Place the pipette over the beaker containing Acetate buffer.
07:45	Pour 0.2 ml into buffer solution.
07:49	Observe the change in pH. Notice that there is not much change in pH.
07:57	Now add small amount of base to the buffer solution.
08:02	Withdraw 0.2 ml of 0.1 M sodium hydroxide(NaOH) using disposable pipette.
08:09	Place the pipette over the beaker containing buffer. Pour 0.2 ml into buffer solution.
08:17	Observe the pH Meter. Notice that there is no much change in the pH.
08:24	Add acid and base to the buffer solution a few more times and check the pH.
08:47	Let us summarize. In this tutorial we have learnt to, Prepare 0.5 M Acetate buffer of pH 3.6.
08:57	Tested buffering action with small amounts of hydrochloric acid(HCl) and sodium hydroxide(NaOH).
09:04	As an assignment, Prepare pH 5.0 Acetate buffer and test with small amounts of acid and base.
09:13	Hint: use 14.7 ml of 0.5 M Acetic acid and 35.3 ml of 0.5 M Sodium acetate.
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09:59	This tutorial is contributed by Snehalatha kaliappan and Madhuri Ganapathi from IIT Bombay Thank you for joining.

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