Question

What are acids? Give any two examples. Explain the effect of an acid on an indicator.

Hint:

Strong acids release more $H^+$ ions, while weak acids release fewer ions in solution.

Answer 1

Step 1: Definition
Acids are substances which produce hydrogen ions ($H^+$ or $H_{3}O^+$) in aqueous solution.
Step 2: Examples
Hydrochloric acid ($HCl$)
Sulphuric acid ($H_{2}SO_{4}$)
Step 3: Effect on Indicators
Acids change the colour of indicators:
Litmus: Turns blue litmus to red.
Methyl Orange: Turns orange to red.
Phenolphthalein: Remains colourless in acids.
Step 4: Scientific Reason
Indicators are weak organic dyes whose molecular structure changes in presence of $H^+$ ions, leading to colour change.
Step 5: Applications
Acid-base indicators are widely used in chemical laboratories, titrations, and testing soil pH.
Final Answer:
Acids release hydrogen ions in solution. Examples: $HCl$, $H_{2}SO_{4}$. They turn blue litmus red and show distinct colour changes with indicators.