Indicators
An indicator is a substance which changes color in the presence of acids or alkalis. The pH scale is a standard scale, which is used for measuring the approximate strength of an acid or an alkali solution. This note provides an information about the indicator, its type and features.
Summary
An indicator is a substance which changes color in the presence of acids or alkalis. The pH scale is a standard scale, which is used for measuring the approximate strength of an acid or an alkali solution. This note provides an information about the indicator, its type and features.
Things to Remember
- An indicator is a substance which changes color in the presence of acids or alkalis.
- In the laboratory, we use three indicators. These are litmus, phenolphthalein and methyl orange.
- Many red or blue colored flowers contain natural dyes which can be used as indicators.
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Indicators
An indicator is a substance which changes color in the presence of acids or alkalis. In the laboratory, we use three indicators. These are litmus, phenolphthalein, and methyl orange.
| Indicator | Acid | Base |
| Red litmus | No change in color | Blue in color |
| Blue litmus | Red in color | No change in color |
| Phenolphthalein | Colorless | Rose color |
| Methyl orange | Red in color | Yellow in color |
Turmeric powder mixed with water is a bright orange-yellow which turns a brick red in the presence of alkali. Indicator can be prepared by boiling, mashing and straining a finely chopped beetroot. Many red or blue colored flowers contain natural dyes which can be used as indicators.
pH Scale
The pH scale is a standard scale, which is used for measuring the approximate strength of an acid or an alkali solution.
The pH scale has ranged from 1 to 14. Acidic solutions have a pH value less than 7 while alkaline solutions have a pH value greater than 7. Distilled water has pH value 7 and is called neutral substance. Strong acids have pH value 1 or 2 while strong alkali's have pH value 13 or 14.
From the pH scale, we can say that higher the hydrogen ion concentration, lower is the pH value and vice versa.
Lesson
Acid, Base and Salt
Subject
Science
Grade
Grade 8
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