11.30. A certain salt X, gives the following results.
(i) Its aqueous solution is alkaline to litmus.
(ii) It swells up to a glassy material Y on strong heating.
(iii) When conc.H2SO4is added to a hot solution of X, white crystal of an acid Z separates out.
Write equations for all the above reactions and identify X, Y and Z. (Advance)
11.30. A certain salt X, gives the following results.
(i) Its aqueous solution is alkaline to litmus.
(ii) It swells up to a glassy material Y on strong heating.
(iii) When conc.H2SO4is added to a hot solution of X, white crystal of an acid Z separates out.
Write equations for all the above reactions and identify X, Y and Z. (Advance)
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1 Answer
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The compounds X, Y and Z are borax, sodium metaborate + boric anhydride and boric acid respectively.
When borax is heated, it first swells and then forms a transparent glass like bead of sodium meta borate and boric anhydride.
Na2B4O7 à2NaBO2+B2O3+10H2O
(Borax) (sodium metaborate) (Boric anhydride)
Aqueous solution of borax is alkaline due to formation of strong base NaOH.
Hence, it turns red litmus blue.
Na2B4O7 +7 H2O → 4H3BO3 + 2NaOH
Borax reacts with sulphuric acid to form boric acid and sodium sulphate.
Na2B4O7 + H2SO4 + 5 H2O → 4H3BO3 + Na2SO4
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