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