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Science · 2025 · 3 marks
CBSE 2025 · Region 6 · Set 2 · Q28
(a) In an experiment a student dipped pH papers in four different solutions A, B, C and D and reported his observation as given below: (i) In which…
In an experiment a student dipped pH papers in four different solutions $\displaystyle \mathrm{A}, \mathrm{B}, \mathrm{C}$ and D and reported his observation as given below :
| Solution | A | B | C | D |
| Colour of pH paper | Light green | Blue | Green | Red |
(i)
In which one of these solutions is the concentration of
(1)
hydrogen / hydronium ions; ($\displaystyle 2$) hydroxyl ions maximum ?
(ii)
Give one example each of the two solutions identified in
(i)
above.
(iii)
What would be the pH of the resultant mixture obtained when these two solutions are mixed together in equal proportions? Justify your answer.
(i)
Name the gas liberated when an acid reacts with a metal. How is this gas tested ?
(ii)
Write the chemical equation for the reaction of zinc metal with
(1)
hydrochloric acid, and
(2)
sodium hydroxide Name the compound of zinc obtained in each case.
Marking-scheme solution
(a) (i)
(1) \(\displaystyle \mathrm{H}^{+}\)ion concentration maximum in Solution D.
(2) \(\displaystyle \mathrm{OH}^{-}\)ion concentration maximum in Solution B.
(ii) Example of D: HCl/ \(\displaystyle \mathrm{H}_{2} \mathrm{SO}_{4} / \mathrm{HNO}_{3}\)
Example of B : NaOH / KOH
(iii)
When a strong acid and a strong base are mixed in equal proportions, the resulting solution will have a pH of $\displaystyle 7$, it will be neutral.
Reason- The acid and base neutralize each other completely, forming water molecules and leaving no excess hydrogen or hydroxide ions
(b) (i)
Hydrogen
Hydrogen burns with a pop sound
(ii) ($\displaystyle 1$) \(\displaystyle \mathrm{Zn}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2}\) Zinc Chloride
(2) \(\displaystyle \mathrm{Zn}+2 \mathrm{NaOH} \rightarrow \mathrm{Na}_{2} \mathrm{ZnO}_{2}+\mathrm{H}_{2}\) Sodium Zincate
All Acids, Bases and Salts questions2025 question paperNCERT solutions: Acids, Bases and SaltsPractice Acids, Bases and Salts →
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CBSE Class 10 Science past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.