Question 10 — Rakshita designed an experiment taking - Questions at the end of the chapter - Chapter 9 Class 7 - Life Processes in Animals (Curiosity)
Last updated at June 1, 2026 by Teachoo
Q 10
Question
Rakshita designed an experiment taking two clean test tubes, A and B and filled them with lime water as shown in the figure. In test tube A, the surrounding air that we inhale was passed on by sucking air from the pipe, and in test tube B, the exhaled air was blown through the pipe (Fig. 9.16). What do you think she is trying to investigate? How can she confirm her findings?
Fig. 9.16: Rakshita's experimental setup comparing inhaled and exhaled air
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Rakshita is investigating whether exhaled air contains more carbon dioxide than inhaled air.
Explanation
Test tube A (inhaled air): lime water stays clear — inhaled air has very little carbon dioxide (~0.04%).
Test tube B (exhaled air): lime water turns milky — exhaled air contains more carbon dioxide (~4–5%).
Lime water turns milky when it reacts with carbon dioxide — this confirms the presence of CO₂ in exhaled air.
To confirm findings:
She can repeat the experiment multiple times to check for consistent results. She can also compare the time taken for lime water to turn milky in test tube B — faster clouding means more carbon dioxide.
Exhaled air has more CO₂ than inhaled air. Lime water turning milky is the confirmation test.
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