The s-Block Elements

Question 169
CBSEENCH11007147

How would you explain that BeO is insoluble but BeSO4 is soluble in water?

Solution

BeO is covalent in nature due to its smaller size, high ionisation enthalpy and high electronegativity and therefore it is insoluble in water. On the order hand, BeSO4 is ionic. Also because of small size of Be2+ ion, the hydration enthalpy of BeSO4 is much higher than its lattice enthalpy. Thus BeSO4 is highly soluble in water.

Question 170
CBSEENCH11007148

How would you explain that BaO is insoluble but BeSO4 is soluble in water?

Solution
BaO and BaSO4 are ionic compounds. Further the size of O2– ion is much smaller as compared to that of SO42– ion. Also, a bigger anion stabilises a bigger cation more than a smaller anion stabilises a bigger cation. As a result lattice enthalpy of BaO is much less than that of BaSO4 and hence BaO is insoluble in water while BaSO4 is soluble.
Question 171
CBSEENCH11007149

How would you explain that BaO is insoluble but BeSO4 is soluble in water?

Solution
BaO and BaSO4 are ionic compounds. Further the size of O2– ion is much smaller as compared to that of SO42– ion. Also, a bigger anion stabilises a bigger cation more than a smaller anion stabilises a bigger cation. As a result lattice enthalpy of BaO is much less than that of BaSO4 and hence BaO is insoluble in water while BaSO4 is soluble
Question 172
CBSEENCH11007150

Explain why halides of beryllium fume in moist air but other alkaline earth metal halides do not.

Solution
BeCl2 reacts with moisture to form HCl while other halides do not.
BeCl subscript 2 space plus space 2 straight H subscript 2 straight O space rightwards arrow space Be left parenthesis OH right parenthesis subscript 2 plus 2 HCl

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