Sl. No. Activity Observations Inference
1. Litmus Paper Test
In the beginning of experiment:
Dip blue litmus paper in test tube A
Dip red litmus paper in test tube B
(i) n = ___ ; action on red litmus paper
action on blue litmus paper
(ii) n = ___ ; action on red litmus paper
action on blue litmus paper
(iii)n = ___ ; action on red litmus paper
action on blue litmus paper
(iv)n = ___ ; action on red litmus paper
action on blue litmus paper
After adding n drops of dil. HCl from test
tube A in dil. NaOH in test tube B
No change
action on blue litmus paper
The solution in test
tube B is
neutralised
No change
Thermal Change
After the completion of litmus test, touch
the test tube B from outside
Heat absorbed/evolved during the
reaction
Cold/Warm Reaction is
endothermic/
exothermic
Answers
In the beginning of experiment:
- Dip blue litmus paper in test tube A
- Dip red litmus paper in test tube B
(i) n = 0 ; action on red litmus paper: no change
action on blue litmus paper: no change
(ii) n = 1 ; action on red litmus paper: no change
action on blue litmus paper: no change
(iii)n = 2 ; action on red litmus paper: no change
action on blue litmus paper: no change
(iv)n = 3 ; action on red litmus paper: no change
action on blue litmus paper: no change
After adding n drops of dil. HCl from test
tube A in dil. NaOH in test tube B
No change
action on blue litmus paper: no change
The solution in test tube B is neutralized
Thermal Change: Cold (Exothermic)
After the completion of litmus test, touch the test tube B from outside. Heat absorbed/evolved during the reaction: Heat is not absorbed or evolved during this reaction. It's endothermic.
Litmus paper is a type of indicator paper that changes color when it comes into contact with an acidic or basic solution.
- Blue litmus paper turns red in acidic solutions, while red litmus paper turns blue in basic solutions.
- In the beginning of the experiment, before any drops of dilute HCl are added to dilute NaOH in test tube B, the blue litmus paper in test tube A would not change color because it is in a neutral solution, and the red litmus paper in test tube B would not change color because it is also in a neutral solution.
- As n drops of dilute HCl are added to the dilute NaOH in test tube B, the solution becomes less basic and eventually neutralized, so the blue litmus paper would not change color, and the red litmus paper would not change color.
- When an acid and a base neutralize each other, they form a salt and water. This reaction is exothermic, meaning it releases heat energy. As the reaction proceeds, the test tube will become cold to touch.
- In summary, the litmus test in this experiment is used to determine the acidity or basicity of the solutions in test tube A and test tube B, the neutralization of acid and base is confirmed by the litmus test, and the exothermic nature of the neutralization reaction is confirmed by the thermal change observed.
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