VITEEE 2015 :: Chemistry :: General questions

• Chemistry - General questions

In keto-enol tautomerism of dicarbonyl compounds; the enol-form is preferred in contrast to the keto-form, this is due to 

Answer:

Explanation:

resonance stabilisation of enol form is 

 In benzene  , the triple bond consists of 

Answer:

Explanation:

In benzene, the triple bond consists of one $sp^{2}-sp^{2}$ σ-sigma bond, one $sp^{2}-sp^{2}$  π-bond and one p-p π-bond 

Consider the following changes

$M(s)\rightarrow M(g) $  ......(i)

$M(g)\rightarrow M^{2+}(g)+2e^{-} $   ...(2)

$M(g)\rightarrow M^{+}(g)+e^{-} $    ....(3)

$M^{+}(g)\rightarrow M^{2+}(g)+e^{-} $  .....(4)

$M^{}(g)\rightarrow M^{2+}(g)+2e^{-} $   .......(5)

The second ionisation energy of M  could be determined from the energy values associated  with

Answer:

Explanation:

The amount  of energy required to take out an electron from the monopositive cation is called second ionisation energy

$M^{}(g)\rightarrow M^{2+}(g)+2e^{-} $  ....(v)

 $M^{}(g)\rightarrow M^{+}(g)+e^{-} $   ....(iii)

 On substracting eq(iii) from eq.(v)  we get,

 $M\rightarrow M^{2+}+e^{-} $

Point out incorrect stability order

Answer:

Explanation:

Increasing order of stability

(a)   $[Cu(NH_{3})_{4}]^{2+}< [Cu(en)_{2}]^{2+}<[Cu(trien)]^{2+}$

 Their  formation of entropy increases in the same order. Ligand denticity is increased

(b)  $[{Fe(H_{2}O})_{6}]^{3+}< [Fe(NO_{2})_{6}]^{3-}<[Fe(NH_{3})_{6}]^{3+}$

$\because$  NH₃  is weaker ligand than NO₂^-

 $\therefore$ The correct stability order is 

$[{Fe(H_{2}O})_{}]^{3+} <[Fe(NH_{3})_{6}]^{3+}<[Fe(NO_{2})_{6}]^{3-}$

(c) $[{Co(H_{2}O})_{6}]^{3+} <[Rh(H_{2}O)_{6}]^{3+}<[Ir(H_{2}O)_{6}]^{3+}$ 

 Z_eff  value increases from Co³⁺ to Ir³⁺

(d)  $[{Cr(NH_{3}})_{6}]^{+} <[Cr(NH_{3})_{6}]^{2+}<[Cr(NH_{3})_{6}]^{3+}$

O.S of Cr atom increases from +1 to +3

 Which two sets  of reactants best represents the amphoteric character of Zn(OH)₂ ?

Set I:  $Zn(OH)_{2}(s)$ and $OH(aq)$

Set II: $Zn(OH)_{2}(s)$ and $H_{2}O(l)$

Set III:   $Zn(OH)_{2}(s)$ and $H^{+}(aq)$

Set IV:   $Zn(OH)_{2}(s)$ and $NH_{3}(aq)$

Answer:

Explanation:

$Zn(OH)_{2}+ 2O^{-}H\rightarrow ZnO_{2}^{2-}+2H_{2}O$

  Acid     Base                    Salt           water

$Zn(OH)_{2}+ 2H^{+} \rightarrow Zn^{2+}+2H_{2}O$

 Base         Acid                  Salt          water

 The amphoteric character of Zn (OH)₂ is represented by I and III

• Chemistry - General questions