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Science · 2023 · 3 marks
CBSE 2023 · Region 6 · Set 3 · Q28
(a) (i) What property do acids and bases have in common? Explain it with an example. (ii) A compound which is prepared from gypsum has the property…
(a)(i)
What property do acids and bases have in common ? Explain it with an example.
(ii)
A compound which is prepared from gypsum has the property of hardening when mixed with water. Identify the compound and write its formula. How is this compound prepared? Describe it in the form of a chemical equation only.
OR
(b)(i)
Write the chemical name and Molecular formula of tooth enamel.
(ii)
How does it get corroded? What is the preventive measure for this ?
Marking-scheme solution
(i)
Acids produce \(\displaystyle \mathrm{H}^{+}\)ions and bases produce \(\displaystyle \mathrm{OH}^{-}\)ions when added in water. /
\[\mathrm{HCl}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{Cl}^{-}
\]
\(\displaystyle \mathrm{NaOH} \xrightarrow{\mathrm{H} 2 \mathrm{O}} \mathrm{Na}^{+}+\mathrm{OH}^{-}\)
(ii)
• Plaster of Paris/Calcium sulphate hemihydrate
\(\displaystyle \left(\mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}\right)\)
\(\displaystyle \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} \xrightarrow{373 \mathrm{~K}} \mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}+1 \frac{1}{2} \mathrm{H}_{2} \mathrm{O}\)
(i)
Calcium phosphate / Calcium hydroxyapatite
\[\left(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\right)
\]
(ii)
Tooth decay starts when the pH of the mouth is lower than 5.5. Bacteria present in the mouth produces acid by degrading sugar and food particles.
Using Toothpaste / Cleaning the mouth after every meal.
All Acids, Bases and Salts questions2023 question paperNCERT solutions: Acids, Bases and SaltsPractice Acids, Bases and Salts →
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CBSE Class 10 Science past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.