BASIC CONCEPTS
(MCQ)
What does the litmus test detect?
A. Proteins
B. Acidity or basicity
C. Sugars
D. Lipids
Answer: B
Explanation: The litmus test is used to determine whether a substance is acidic or basic based on color change.
(MCQ)
What color is blue litmus paper in neutral solution?
A. Red
B. Blue
C. Green
D. Yellow
Answer: B
Explanation: In neutral conditions, litmus paper does not change color.
(MCQ)
Which of the following is a carboxylic acid?
A. Ethanol
B. Ethanoic acid
C. Methane
D. Propane
Answer: B
Explanation: Ethanoic acid contains the –COOH group.
(MCQ)
What is the first step in the litmus test?
A. Heating sample
B. Applying sample to litmus paper
C. Adding reagent
D. Cooling solution
Answer: B
Explanation: The sample is placed onto or dipped with litmus paper.
(MCQ)
Why is the litmus test useful?
A. Measures exact pH
B. Identifies acids and bases quickly
C. Detects proteins
D. Measures sugar
Answer: B
Explanation: It gives a quick indication of acidity/basicity.
(MCQ)
Which functional group defines carboxylic acids?
A. –OH
B. –NH₂
C. –COOH
D. –CHO
Answer: C
Explanation: The carboxyl group (–COOH) is responsible for acidic properties.
(True/False)
Red litmus turns blue in acidic solutions.
Answer: False
Explanation: Red litmus stays red in acids; it turns blue only in bases.
(True/False)
Carboxylic acids have a sour taste.
Answer: True
Explanation: Many acids (like vinegar) taste sour, though tasting chemicals in labs is unsafe.
(True/False)
Heating is required for the litmus test.
Answer: False
Explanation: The test works at room temperature.
(MCQ)
Which sample would turn blue litmus red?
A. Sodium hydroxide
B. Water
C. Ethanoic acid
D. Ammonia
Answer: C
Explanation: Ethanoic acid is acidic.
(True/False)
All acids turn litmus paper blue.
Answer: False
Explanation: Acids turn blue litmus red, not the other way around.
(True/False)
Litmus can distinguish between strong and weak acids.
Answer: False
Explanation: Litmus only indicates whether a solution is acidic or basic—not strength.
(MCQ)
What happens when a carboxylic acid dissolves in water?
A. Releases OH⁻
B. Releases H⁺
C. Forms gas
D. Becomes neutral
Answer: B
Explanation: It donates hydrogen ions, making the solution acidic.
(MCQ)
What is observed during the test?
A. Gas formation
B. Color change
C. Precipitate
D. Temperature change
Answer: B
Explanation: The key observation is a color change in the indicator.
(True/False)
The litmus test is qualitative.
Answer: True
Explanation: It gives descriptive, not numerical, results.
(MCQ)
Which property is being tested using litmus?
A. Solubility
B. pH
C. Temperature
D. Density
Answer: B
Explanation: Litmus indicates whether a solution is acidic or basic (pH level).
(MCQ)
What happens to red litmus in a base?
A. Turns blue
B. Turns green
C. Turns yellow
D. No change
Answer: A
Explanation: Bases turn red litmus blue.
(True/False)
Carboxylic acids fully ionize in water.
Answer: False
Explanation: They are weak acids and only partially ionize.
(True/False)
Safety precautions are unnecessary.
Answer: False
Explanation: Proper lab safety is always required.
(True/False)
Litmus test works only for carboxylic acids.
Answer: False
Explanation: It works for all acids and bases, not just carboxylic acids.
(MCQ)
Why do carboxylic acids behave as acids?
A. They release OH⁻ ions
B. They release H⁺ ions
C. They absorb electrons
D. They neutralize bases only
Answer: B
Explanation: Carboxylic acids donate hydrogen ions (H⁺) in solution.
(True/False)
Litmus changes color due to a chemical reaction with H⁺ ions.
Answer: True
Explanation: The indicator molecules respond to hydrogen ion concentration.
(MCQ)
Which factor affects acidity strength?
A. Length of carbon chain
B. Functional group
C. Electron-withdrawing groups
D. All of the above
Answer: D
Explanation: All these influence how easily H⁺ is released.
(MCQ)
What is used to handle samples safely?
A. Bare hands
B. Pipette
C. Thermometer
D. Balance
Answer: B
Explanation: Pipettes allow controlled and safe transfer of liquids.
(MCQ)
Which factor could affect results?
A. Contamination
B. Improper handling
C. Concentration
D. All of the above
Answer: D
Explanation: All can influence accuracy.