Virtual Lab

Introduction:

Many natural substances contain molecules that change colour in aqueous solutions when the solution is changed from a basic to acidic nature or vice versa. Several natural dyes, e.g., the pigments in flowers or the coloured ingredient of turmeric have such properties. Quantitatively pH=-log[H⁺], is a measure of the acidity or basicity of a system. It varies from close to 0 (strongly acidic) to nearly 14(strongly basic).Common acid-base indicators when added in a small amount to a solution, give a visual indication of the pH of the solution. When an acid is neutralised by a base, some indicators show a sharp change in color near the point of neutralisation. These are also called halochromic compounds. In this experiment, we watch colours of solutions of different nature (acidic or basic) with indicators in a self learning mode.

Virtual Lab

Quiz

References

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Objective:
Study the color change of an indicator in different pH solutions.

Manual:
Follow the following steps to perform the experiment:

Select the type of acid/base and indicator.

Start the experiment.

Add indicator.

Observe color change.

Fill in the table.

Quiz:

Try to find the answer of the following questions by yourself

What is the pH value of water?

Which Indicator you will choose to detect the titration point of a weak acid and a strong base?

Name some naturally occurring acid-base indicators.

References:

The following references may be checked

Molecular biology problem solver: a laboratory guide By Alan S. Gersteinh

http://www.ph-meter.info/

Theory:
Acid-base indicators are frequently weak acids or bases. The basic principle is given as follows

Here HInd stands for the acid form and Ind^- for the conjugate base of the indicator. It is the ratio of these that determines the color of the solution and that connects the color to the pH value. Here the equation is derived from the acidity constant of the indicator.

Acid Base Indicators

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International Institute of Information Technology, Hyderabad (IIIT-H)

Center for IT in Education (cITe)

Earthquake Engg. (EERC)

Computational Natural Sciences & Bioinformatics (CCNSB)

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