A certain salt (X) gives the following $$tests(i)$$ Its aqueous solution is alkaline to litmus.(ii) On strongly heating it swells to give a glassy bead.(iii) When concentrated sulphuric acid is added to a hot concentrated solution of (X), crystals of $$H3BO3$$ separate out. Identify the colour of these crystals.

Question

A certain salt (X) gives the following $$tests(i)$$ Its aqueous solution is alkaline to litmus.(ii) On strongly heating it swells to give a glassy bead.(iii) When concentrated sulphuric acid is added to a hot concentrated solution of (X), crystals of $$H3BO3$$ separate out. Identify the colour of these crystals.

Infinity Learn · Accepted Answer

X  is borax, $$Na2B4O7.10H2O$$ (i)  $$Na2B4O7$$  $$+$$ $$7H2O$$  ⇌  $$2NaOH(Strong$$ $$Base)$$  $$+$$ $$4H3BO3(Weak$$ $$acid)Due$$ to presence of NaOH, the aqueous solution is alkaline to litmus.(ii) $$Na2B4O7.10H2O$$  →swellsHeat   $$Na2B4O7$$  $$+$$  $$10H2O$$  → $$2NaBO2$$   $$+$$   $$B2O3Glassy$$ bead (iii) $$Na2B4O7$$ $$+$$ $$H2SO4$$ $$+$$ $$5H2O$$  → $$Na2SO4$$  $$+$$  $$4H3BO3White$$ crystals

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