Question

Select the synthetic indicator from among the given options.

• A. Turmeric
• B. Cabbage juice
• C. Litmus solution
• D. Methyl orange

Answer 1

Answer:

D. Methyl orange

Indicators in Chemistry

Types of Indicators

• Natural Indicators: These are obtained from natural sources like plants and animals. Examples include litmus (extracted from lichens), red cabbage juice, and turmeric.

• Synthetic Indicators: These are man-made chemical compounds designed to indicate the acidic or basic nature of a solution through a distinct color change.

Methyl Orange

• Methyl orange is a synthetic indicator.

• It is widely used in acid-base titrations.

• Color Changes:

  • In acidic solutions (pH < 3.1), methyl orange appears red.

  • In neutral solutions (pH between 3.1 and 4.4), it appears orange.

  • In basic solutions (pH > 4.4), it appears yellow.

• The pH range over which the color change occurs is known as its 'pH range' or 'transition range'. For methyl orange, this range is approximately 3.1 to 4.4.

Other Synthetic Indicators (for comparative understanding)

• Phenolphthalein: Colorless in acidic solution, pink in basic solution. Transition range: 8.2-10.0.

• Methyl Red: Red in acidic solution, yellow in basic solution. Transition range: 4.4-6.2.