The s-Block Elements Questions and Answers Part-12

1. A salt on treatment with dil. HCl gives a pungent smelling gas and a yellow precipitate. The salt gives green flame test and a yellow precipitate with potassium chromate. The salt is
a) \[NiSO_{4}\]
b) \[BaS_{2}O_{3}\]
c) \[PbS_{2}O_{3}\]
d) \[CuSO_{4}\]

Answer: b
Explanation: Since the salt on treatment with dil. HCl gives a pungent smelling gas (SO2 ) and a yellow ppt., it must contain S2O32– (thiosulphate ion) and further since it gives green flame test, it must contain Ba2+ ion. Hence salt is BaS2O3 .

2. A metal is burnt in air and the ash on moistening smells of \[NH_{3}\]  . The metal is
a) Na
b) Fe
c) Mg
d) Al

Answer: c
Explanation: Mg burns in air to form Mg3N2 which then reacts with H2O to form NH3 .

3. The carbide of which of the following metals on hydrolysis gives allylene or propyne?
a) Be
b) Ca
c) Al
d) Mg

Answer: d
Explanation: Mg

4. Magnesium burns in CO2 to form?
a) MgO + C
b) MgO + CO
c) \[MgCO_{3}\]
d) MgO

Answer: a
Explanation: MgO + C

5. Which of the following will liberate hydrogen by its reaction with hydrochloric acid?
a) Copper
b) Phosphorus
c) Mercury
d) Magnesium

Answer: d
Explanation: Since the electrode potential of Mg is lower than that of hydrogen (Eº = 0.0 volt), it will reduce H+ ions to H2 gas

6. Alkaline earth metals are not found free in nature because of
a) their thermal instability
b) their low melting points
c) their high boiling points
d) their greater chemical reactivity

Answer: d
Explanation: their greater chemical reactivity

7. Ionic hydride is not formed by
a) Be
b) Ca
c) Ba
d) Sr

Answer: d
Explanation: BeH2 is covalent.

8. Which of the following alkaline earth metal hydroxides is amphoteric in character
a) \[Be\left(OH\right)_{2}\]
b) \[Ca\left(OH\right)_{2}\]
c) \[Sr\left(OH\right)_{2}\]
d) \[Ba\left(OH\right)_{2}\]

Answer: a
Explanation: Be(OH)2 is amphoteric while Ca(OH)2 , Sr(OH)2 and Ba(OH)2 are all basic.

9. A chloride dissolves appreciably in cold water. When placed on a Pt wire in Bunsen flame, no distinctive colour is noted. Which cation could be present?
a) \[Be^{2+}\]
b) \[Ba^{2+}\]
c) \[Pb^{2+}\]
d) \[Ca^{2+}\]

Answer: a
Explanation: Due to very high I.E. of Be, its valence electrons require high energy to remove (excite) which is not available in Bunsen flame hence Be2+ ions do not impart colour to the flame.

10. Halides of alkaline earth metals form hydrates such as \[MgCl_{2}.6H_{2}O,CaCl_{2}.6H_{2}O,BaCl_{2}.2H_{2}O\]         and \[SrCl_{2}.2H_{2}O\]   . This shows that halides of group 2 elements
a) are hygroscopic in nature
b) act as dehydrating agents
c) can absorb moisture from air
d) All of the above

Answer: d
Explanation: All of the above