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Byju's Answer

Standard XII

Chemistry

Borax

Ca2B6O11[X]+C...

Question

$C a_{2} B_{6} O_{11} Δ - \to [X] + C a C O_{3} + N a B O_{2}$ (unbalanced equation) Which of the following is/are correct choice(s) for [X]?

The structure of anion of crystalline [

X

] has one boron atom

s p^{3}

hybridized and other three boron atoms

s p^{2}

hybridized

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X

with

N a O H_{(a q)}

gives a compound which on reaction with hydrogen peroxide in alkaline medium yields a compound used as the brightener in soaps

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Hydrolysis of [

X

] with

H C l

H_{2} S O_{4}

yields a compound which on reaction with

H F

gives fluoroboric acid

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[

X

] on heating with chromium salts in oxidizing flame gives green colored bead

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Solution

The correct options are
B $X$ with $N a O H_{(a q)}$ gives a compound which on reaction with hydrogen peroxide in alkaline medium yields a compound used as the brightener in soaps
C Hydrolysis of [ $X$ ] with $H C l$ or $H_{2} S O_{4}$ yields a compound which on reaction with $H F$ gives fluoroboric acid
D [ $X$ ] on heating with chromium salts in oxidizing flame gives green colored bead
The compound X is borax $(N a_{2} B_{4} O_{7})$ . It is prepared by boiling finely powdered colemanite mineral $(C a_{2} B_{6} O_{11})$ with sodium carbonate solution.

$C a_{2} B_{6} O_{11} + 2 N a_{2} C O_{3} \to 2 C a C O_{3} + N a_{2} B_{4} O_{7} + 2 N a B O_{2}$

The statements (B), (C) and (D) are correct. The statement (A) is incorrect.

(A) The structure of anion of crystalline [X] has two boron atoms $s p^{3}$ hybridized and other two boron atoms $s p^{2}$ hybridized.

(B) X with NaOH(aq), gives sodium metaborate $N a B O_{2}$ which on reaction with hydrogen peroxide in alkaline medium yields hexahydrate sodium tetraaquadiperoxoborate (III).

$2 N a B O_{2} + 2 H_{2} O_{2} + 6 H_{2} O \to N a_{2} [B_{2} (O_{2})_{2} (O H)_{4}] ∙ 6 H_{2} O$

(C) Hydrolysis of [X] with $H C l$ or $H_{2} S O_{4}$ yields boric acid which on reaction with $H F$ gives fluoroboric acid.

$N a_{2} B_{4} O_{7} + H_{2} S O_{4} \to N a_{2} S O_{4} + H_{2} B_{4} O_{7}$
$H_{2} B_{4} O_{7} + 5 H_{2} O \to 4 H_{3} B O_{3}$
$H_{3} B O_{3} + 4 H F \to H [B F_{4}] + 3 H_{2} O$

(D) [X] on heating with chromium slats in oxidizing flame gives green colored bead.
$C r_{2} O_{)} 3 + 3 B_{2} O_{3} \to 2 C r (B O_{2})_{3} (chromium metaborate green)$
This is borax bead test.

Suggest Corrections

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