Multiple Choice QuestionsMetals are good conductor of electricity because they contain :
a network structure
ionic bonds
very few valence electrons
free electrons
Which of the following has the highest tendency to give the reaction,
M+(g) M+(aq.) ?
Na
Li
K
Rb
Among the following components of cement which is present in highest amount?
Ca2SiO4
Ca3SiO5
Al2O3
Ca3Al2O6
The pair whose both species are used in antiacid medicinal preparation is
NaHCO3 and Mg(OH)2
Na2CO3 and Ca(HCO3)2
Ca(HCO3)2 and Mg(OH)2
Ca(OH)2 and NaHCO3.
Which of the following is a false statement ?
Fluorine is more electronegative than chlorine
Nitrogen has greater IE1 than oxygen
Lithium is amphoteric
Chlorine is an oxidising agent
Which of the following is a use of alum ?
Making explosives
Bleaching clothes
Water softening
All of the above
The pair of amphoteric hydroxides is
Al(OH)3, LiOH
Be(OH)2, Mg(OH)2
B(OH)3, Be(OH)2
Be(OH)2, Zn(OH)2
Which of the following is only acidic nature?
Be(OH)2
Mg(OH)2
B(OH)3
Al(OH)3
C.
B(OH)3
B(OH)3 in aqueous medium coordinates a molecule of water to form the hydrated species . In this species, B3+ ion, because of its small size, exercises a high polarizing power thereby pulling the sigma electron charge of the coordinated O atom towards itself. The coordinated oxygen, in turn, pulls the sigma electron charge of the OH bond of the attached H2O molecule towards itself. This facilitates the removal of H+ ion from the O- H bond, as shown below.
Thus the solution of B(OH)3 in water acts as a weak acid. That is why it reacts with NaOH solution to produce the sodium salt.
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