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Orthoboric Acid

On the additi...

Question

On the addition of mineral acid to an aqueous solution of borax, the compound formed is:

A

orthoboric acid

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B

boron hydride

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C

metabolic acid

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D

pyroboric acid

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Solution

The correct option is C orthoboric acid
Addition of mineral acid to an aqueous solution of Borax,

Orthoboric acid is formed.

$N a_{2} B_{4} O_{7} + 2 H C l + 5 H_{2} O ⟶ 4 H_{3} B O_{3} + 2 N a C l$

Borax. Hydrochloric Orthoboric acid Sodium chloride Acid

Boric acid is soluble in boiling water. When heated above $170^{o} C$ , it dehydrates, forming metaboric acid $(H B O_{2})$ :

Acid melts at about $236^{o} C$ , and when heated above about $300^{o} C$ further dehydrates, forming tetraboric acid, also called pyroboric acid $(H_{2} B_{4} O_{7})$ .

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Similar questions

A black colored compound (A) on reaction with

d i l . H_{2} S O_{4}

gives a gas (B) which on passing in a solution of acid (C) gives white turbidity (D). Gas (B) when passed in an acidified solution of a compound (E) gives a black precipitate (F) which is soluble in hot concentrated (C). After boiling this solution when an excess of ammonia solution is added, a blue-colored compound (G) is formed. To the solution of (E), on the addition of acetic acid and aqueous potassium ferrocyanide, a chocolate brown precipitate (H) is formed. On the addition of an aqueous solution of

B a C l_{2}

to an aqueous solution of (E), white precipitate insoluble in

H N O_{3}

The gas (B) on passing through an acid (C) gives white turbidity (D) because :

Q. An unknown inorganic compound

(X)

gave the following reaction:
(i) on heating

^{'} X^{'}

gave a residue, oxygen and oxide of nitrogen.
(ii) addition of acetic acid and

K_{2} C r_{2} O_{7}

to its aqueous solution give a yellow precipitate.
(iii) addition of

N a O H

to its aqueous solution first forms a white precipitate, Dissolve in the excess of the reagent.
Identify the compound

(X)

A black colored compound (A) on reaction with dilute

H_{2} S O_{4}

gives a gas (B) which on passing in a solution of acid (C) gives white turbidity (D). Gas (B) when placed in an acidified solution of a compound (E) gives a precipitate (F) soluble in dilute

H N O_{3} .

After boiling this solution, when an excess of

N H_{4} O H

is added, blue colored compound (G) is formed. To this solution on addition of

C H_{3} C O O H

K_{4} [F e (C N)_{6}]

, a chocolate precipitate (H) is obtained. On the addition of an aqueous solution of

B a C l_{2}

to an aqueous solution of E, a white ppt insoluble in

H N O_{3}

Q. When an aqueous solution of borax forms a complex compound, then what is the coordination number of boron in that complex?

Q. Assertion :Borax forms alkaline aqueous solution. Reason: Borax is the salt of a weak acid

(H_{3} {B O}_{3})

and a strong base

(N a O H)

.

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