Tag: some important compounds of boron

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Multiple choice chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

Which one of the following statements about $H _3BO _3$ is not correct?

  1. It is a strong tribasic acid

  2. It is a prepared by acidifying an aqueous solution of borax
  3. It has a layer structure in which planar $BO _3$ units are joined by hydrogen bonds

  4. It does not act as proton donor as it acts as a Lewis acid by accepting hydroxyl ions
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

It is weak monoprotic acid and it does not act as proton donor but removes proton from water.

Multiple choice chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

$B _{2}Ca _{6}O _{11}+ Na _{2}CO _{3}\overset{\Delta }{\rightarrow}\left [ X \right ]+CaCO _{3}+NaBO _{2}$ (unbalanced equation)
Correct choice(s) for [X] is/are:

  1. structure of anion of crystalline [X] has one boron atom sp$^{3}$ hybridised and other three boron atoms sp$^{2}$
    hybridised

  2. X with NaOH (aq.) gives a compound which on reaction with hydrogen peroxide in alkaline medium yields
    a compound used as brightner in soaps
  3. hydrolysis of [X] with HCl or H$ _{2}$SO$ _{4}$ yields a compound which on reaction with HF gives fluoroboric acid

  4. [X] on heating with chromium salts in oxidising flame gives green coloured bead in cold
Reveal answer Fill a bubble to check yourself
B,C,D Correct answer
Explanation

Compound [X] is Na$ _{2}$B$ _{4}$O$ _{7}$
(A) two boron atoms are $sp^{2}$ while other two boron atoms are $sp^{3}$ hybridised.
(B) product is sodium peroxoborate which is used as brightner in soaps.
(C) $H _{3}BO _{3}$ is formed which with HF gives $HBF _{4}$.
(D) Green bead in oxidising as well as in reducing flame in cold.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Boron can undergo the following reactions with the given enthaly changes:
Assume no other reactions are occurring. If in a container (operating at constant pressure) which is isolated from the surrounding, mixture of are passed over excess of B(s), then calculate the molar ratio so that temperature of the container do not change :
${\text{2B}}\left( {\text{s}} \right){\text{ + }}\dfrac{{\text{3}}}{{\text{2}}}{{\text{O}} _{\text{2}}}\left( {\text{g}} \right) \to {{\text{B}} _{\text{2}}}{{\text{O}} _{\text{3}}}\left( {\text{s}} \right);\;\Delta H =  - 1260\;KJ$
${\text{2B}}\left( {\text{s}} \right){\text{ + 3}}{{\text{H}} _{\text{2}}}\left( {\text{g}} \right) \to {{\text{B}} _2}{H _6}\left( g \right);\;\Delta H = 30KJ$

  1. 15 : 3

  2. 42 : 1

  3. 1 : 42

  4. 1 : 84
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For the temperature of the isolated container to remain constant, the total enthalpy change for the reactions must be zero. Let x moles of B react to form B2O3 and y moles of B react to form B2H6. Using the given stoichiometry and enthalpy values, we solve for the ratio x:y to find the correct molar ratio.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

For healthy growth of plants, boron is an essential:

  1. minor nutrient

  2. major nutrient

  3. both

  4. major metal
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Boron is essential for the growth of higher plants. The primary function of the element is to provide structural integrity to the cell wall in plants. 


Other functions likely include the maintenance of the plasma membrane and other metabolic pathways.

So it is essential micronutrient for plants.

Option A is correct.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Diborane undergoes cleavage and gives aduct with
(i) CO
(ii) $ H _2O $
(iii) $ N(Me) _3 $
(iv) $ NH _3 $

  1. i, ii

  2. i, iii

  3. ii, iii

  4. i, iv
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Diborane (B2H6) undergoes symmetrical or unsymmetrical cleavage with various Lewis bases. It forms adducts with CO and NH3, among others. Option A is the most standard representation of these reactions.