Difference between revisions of "ChemCollective-Virtual-Labs/C2/Dilutions-and-pH-Measurement/English"

Title Slide

Learning Objectives

• Change in pH for solutions of acid and base on dilution.
• Variation in pH by common-ion effect for weak acids and bases.

Pre-requisites

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ChemCollective Vlabs interface.

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System Requirement

• Mac OS version 10.10.5
• ChemCollective Vlabs version 2.1.0
• Java version 8.

Measurement of pH

10 Times Dilution:

0.1 M HCl to 0.01 M Hcl

0.1M NaOH to 0.01 M NaOH.

• 0.1 molar Hydrochloric acid to 0.01 molar Hydrochloric acid.
• 0.1 molar sodium hydroxide to 0.01 molar sodium hydroxide.

For this experiment,

2 ml of 0.1 M Hydrochloric acid or sodium hydroxide is diluted to 20 ml with distilled water.

Double-click on vlabs.exe file.

Double-click on Strong-acid cabinet .

Double-click on Strong-acids cabinet.

A list of acidic solutions with various strengths opens.

Click on the flask, observe the pH in the pH Meter.

Click on the radio button near Strong-acids cabinet, to close the list.

Click on the flask, observe the pH on the pH Meter.

Note that pH Meter reads 1.

Click on the radio button near Strong-acids cabinet, to close the list.

Double-click to choose 0.1 Molar NaOH.

A list of basic solutions with various strengths opens.

Double-click to choose point one molar NaOH.

Point to the pH Meter.

Click on the radio button.

Note that pH Meter reads 13.

Click on the radio button near Strong-bases cabinet to close the list.

Select Graduated Cylinders.

From the sub-menu, select 10 mL Graduated Cylinder.

Select Graduated Cylinders.

From the sub-menu, select 10 mL Graduated Cylinder to add to the workbench.

From the context menu, select copy.

Move the cursor to a different position.

Right-click and choose Paste option from the menu.

Right-click on the Graduated Cylinder.

From the context menu, select copy.

Place the cursor at a different place.

Right-click and choose Paste option from the menu.

Select Erlenmeyers.

From the sub-menu select 250 mL Erlenmeyer Flask.

Copy and paste the flask using context menu.

Select Erlenmeyers.

From the sub-menu, select 250 mL Erlenmeyer Flask.

We require two flasks.

Right-click to copy and paste.

Type A in the text box and click Ok button.

Right-click on the Graduated Cylind er.

From the Context-menu, select Rename option.

A text box opens. Type A in the text box and click on Ok button.

Similarly, label the other Cylinder as B.

Similarly, label Erlenmeyer Flasks as A and B..

Use set A for acids and set B for bases.

In the transfer amount input bar type, 2.

Click on Pour.

In the Transfer amount input bar, type 2.

Click on Pour.

Move the flask aside.

In the transfer amount input bar type, 18.

Click on Pour.

Move the Distilled water aside.

In the Transfer amount input bar, type 18.

Click on Pour.

Move the Distilled water aside.

Change the transfer mode to realistic transfer.

Click on pour gradually.

Change the transfer mode to Realistic transfer.

Click on Pour button gradually.

Move the Graduated Cylinder A aside.

pH meter reads 2.

Tools >>Transfer bar>>Precise transfer.

In the transfer amount input bar type, 2.

Click on Pour.

Drag 0.1 molar Sodium Hydroxide flask over to Graduated Cylinder B.

Using Tools menu, change the transfer mode to Precise transfer.

In the transfer amount input bar, type 2.

Click on Pour.

Move the flask aside.

In the transfer amount input bar, type 18.

Click on Pour.

In the Transfer amount input bar, type 18.

Click on Pour.

Move the Distilled water aside.

Cylinder B to Flask B.

Tools >>Transfer bar>>Realistic transfer.

Click on Pour button gradually.

Place the Graduated Cylinder B over Flask B.

Change the transfer mode to realistic transfer.

Click on Pour button gradually.

Move the Graduated Cylinder B aside.

pH meter reads 12.

Results

pH is a logarithmic scale, for every 10 times dilution pH changes by 1 unit.

pH of 0.1 M Hydrocholric acid is 1. When diluted, acidity decreases.

After dilution, pH was found to be 2.

Similarly, pH of 0.1 M NaOH is 13. When diluted, alkalinity decreases.

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.

For the next experiment, load a new workbench using File menu.

Click on Workbench 2.

We will demonstrate this, using weak acids and weak bases.

Common ion effect

1. Ethanoic acid and its conjugate base, sodium ethanoate.

2. Ammonia and its conjugate acid, Ammonium Chloride.

1. Ethanoic acid and its conjugate base, sodium ethanoate.

2. Ammonia and its conjugate acid, Ammonium Chloride.

Place the required chemicals from the Stockroom explorer on the workbench.

Double-click to choose 1M Ethanoic acid.

Click on the small button next to Weak-acids cabinet.

A list of weak acid solutions with various strengths opens.

Double-click to choose 1 molar Ethanoic acid.

Close the list.

Double-click to choose 1 molar Ammonia.

A list of weak bases with various strengths opens.

Double-click to choose 1 molar Ammonia solution.

Close the list.

Double-click on 1M Ammonium Chloride.

Double-click on 1 molar Ammonium Chloride solution.

Close the list.

Double-click on 1 molar Sodium Ethanoate.

Double-click on 1 molar Sodium Ethanoate solution from the list.

Close the list.

Right-click to Copy and paste.

We need 4 Beakers for this experiment.

Right-click on the Beaker.

Using copy and paste option make 3 copies of the Beaker.

Text box opens, type A in the text box and click OK button.

Drag and place the Beakers C and D on other side of the workbench.

Place the Beakers C and D on other side of the workbench.

Drag and place Ammonia and its conjugate acid Ammonium Chloride on the other side.

Place Ammonia and its conjugate acid Ammonium Chloride on the other side.

Place 1M Ethanoic acid over beaker A.

Type 25 in the Transfer amount input bar.

Click on pour.

Do the same for beaker C.

Type 25 in the transfer amount input bar.

Click on pour.

Similarly, transfer 25 ml of Ethanoic acid to beaker B.

Move the flask aside.

Type 25 in the Transfer amount input bar.

Click on pour.

Do the same for beaker D.

Move the flask aside.

Type 25 in the transfer text bar.

Click on pour.

Transfer 25 ml of Sodium ethanoate into beaker B.

Place 1 molar Sodium ethanoate flask over beaker B.

Type 25 in the transfer amount input bar.

Click on pour.

Keep the flask aside.

Observe pH meter.

pH meter shows pH value of 2.38.

Observe pH meter.

pH meter shows pH value of 4.76 .

Type 25 in the transfer amount input bar.

Click on pour.

Place 1 Molar Ammonium Chloride flask over beaker D.

Type 25 in the transfer amount input bar.

Click on pour.

Keep the flask aside.

pH meter shows pH value of 11.62.

Observe pH meter.

pH meter shows pH value of 9.25.

Now, let us tabulate the results.

Results

Point to the result.

that is ethanoate ion, ionization of ethanoic acid decreases.

Hence pH value increases.

Similarly, due to the presence of ammonium ion, ionization of Ammonia decreases.

Hence pH value decreases.

Summary

we have learnt to measure-

• Change in pH for solutions of 0.1 Molar Hydrochloric acid and 0.1 Molar Sodium Hydroxide on dilution.
• Variation in pH by common-ion effect for ethanoic acid and ammonia solutions.

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.
• Variation in pH by common-ion effect for ethanoic acid and ammonia solutions.

Assignment

Measure change in pH for-

1 M and 0.01 M Sulphuric acid.

1 M and 0.01 M sodium hydroxide.

Measure change in pH for-

1 M and 0.01 M Sulphuric acid.

1 M and 0.01 M Sodium hydroxide.

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