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The s-block Elements — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryThe s-block Elements3 Marks
Question
  1. Why do we add gypsum in final stages of preparation of cement?
  2. Why does Al dissolve both in acidic and basic.
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Answer

  1. Gypsum is added to regulate its setting time. If it is not added, the cement mixed with water sets into hard mass very quickly. Therefore, gypsum is added to delay and regulate setting time of cement.
  2. Aluminium is amphoteric in nature, therefore, it can dissolve in both HCl and NaOH solutions.
$2\text{Al}+6\text{HCl}\xrightarrow{\ \ \ \ \ \ \\ \ \\ }2\text{AlCl}_3+3\text{H}_2$

$2\text{Al}+2\text{NaOH}+\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ \ \\ \ \\ }2\text{NaAlO}_2+3\text{H}_2\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Sodium meta}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{aluminate}$

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