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The solubility of alkli metals salts in ...

The solubility of alkli metals salts in water is due to the fact that the cations get hydrated by water molecules. The degree of hydration depends upon the size of the cation. If the trend of relative ionic radii is `Cs^(+) gt Rb^(+) gt K^(+) gt Na^(+) gt Li^(+) `.
What is the relative degree of hydration?

A

`Ca_((aq))^(+)gt Rb_((aq))^(+) gt K_((aq))^(+) gt Na_((aq))^(+) gt Li_((aq))^(+)`

B

`Li_((aq))^(+) gt Na_((aq))^(+)gt K_((aq))^(+) gt Rb_((aq))^(+) gt Cs_((aq))^(+)`

C

`Na_((aq))^(+) gt K_((aq))^(+) gt Rb_((aq))^(+) gt Cs_((aq))^(+)gt Li_((aq))^(+)`

D

`Cs_((aq))^(+) gt Na_((aq))^(+) gt Li_((aq))^(+) gt K_((aq))^(+) gt Rb_((aq))^(+)`

Text Solution

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The correct Answer is:
B
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Read the given passage and answer questions number 1 to 5 that follow : Consider the reaction of an alkanamine and ammonia with a proton to compare their basicity. Due to the electron releasing nature of alkyl group, it (R) pushes electrons towards nitrogen and thus makes the unshared electron pair more available for sharing with the proton of the acid. Moreover, the substituted ammonium ion formed formed from the amine gets stabilised due to dispersal of the positive charge by the +I effect of the alkyl group. Hence, alkylamines are stronger bases than ammonia. Thus, the basic nature of aliphatic amines should increase with increase in the number of alkyl groups. This trend is followed in the gaseous phase. The order of basicity of amines in the gaseous phase follows the expected order : tertiary amine > secondary amine > primary amine > NH_(3) . Th trend is not regular in the aqueous state as evident by their pK_(b) values. In the aqueous phase, the substituted ammonium cations get stabilised not only by electron releasing effect of the alkyl group (+I) but also by solvation with water molecules. The greater the size of the ion, lesser will be the solvation and the less stabilised is the ion. What is the basicity order of the following compounds in aqueous solution ? " "C_(2)H_(5)NH_(2), (C_(2)H_(5))_(2)NH, (C_(2)H_(5))_(3)N

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Knowledge Check

  • The solubility iof alkali metal salts in water is due to the fact that the cations get hydrated by water molecules. The degree of hydration depends upon the size of the cation. If the trend of relative ionic radii is Cs^(+) gt Rb^(+) gt K^(+) gt Na^(+) gt Li^(+). What is the relative degree of hydration ?

    A
    `Cs_((aq))^(+) gt Rb_((aq))^(+) gt K_((aq))^(+) gt Na_((aq))^(+) gt Li_((aq))^(+)`
    B
    `Li_((aq))^(+) gt Na_((aq))^(+) gtK_((aq))^(+) gt Rb _((aq))^(+) gt Cs_((aq))^(+)`
    C
    `Na_((aq))^(+) gt K _((aq))^(+) gt Rb _((aq))^(+) gt Cs_((aq))^(+) gt Li_((aq))^(+)`
    D
    `Cs_((aq))^(+) gt Na_((aq))^(+) gt Li_((aq))^(+) gt K_((aq))^(+) gt Rb_((aq))^(+)`

  • Alkali metal salts ionic and soluble in water. The solubility of an ionic compound depends on (i) lattic ethalpy and (ii) hydration enthalpy. These two factor oppose each other. If hydration ethalpy is high, the ions will have greater tendency to be hydrated and therefore the solubility will be high. The smaller the cation, the greater is the degree of hydration. The reducing behaviour of alkali metals in solution is also dependent on the hydration enthalpy besides other factors. The ionic mobility of Li^(o+) is less than of the Na^(o+) ion in solution because

    A
    `Li^(o+)` ion has a high charge density.
    B
    `Li^(o+)` ion has the highest hydration tendency.
    C
    `Li^(o+)` ion has the highest ionisation enthalpy.
    D
    `Li^(o+)` ion has two electrons.

  • Alkali metal salts ionic and soluble in water. The solubility of an ionic compound depends on (i) lattic ethalpy and (ii) hydration enthalpy. These two factor oppose each other. If hydration ethalpy is high, the ions will have greater tendency to be hydrated and therefore the solubility will be high. The smaller the cation, the greater is the degree of hydration. The reducing behaviour of alkali metals in solution is also dependent on the hydration enthalpy besides other factors. The radius of which of the hydrated ion is the highest ?

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    `Li_((aq))^(o+)`
    B
    `Na_((aq))^(o+)`
    C
    `K_((aq))^(o+)`
    D
    `Rb_((aq))^(o+)`

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