Question:

What is the heat of solution of sodium chloride from following data? Hydration energy of $Na^+ = - 389.4\, kJ\, mol^{-1}$ Hydration energy of $Cl^- = - 382.3\, kJ\, mol^{-1}$ Lattice energy of $NaCl = - 776 \,kJ \,mol^{-1}$

Updated On: Jul 7, 2022
  • $+ 8.6\, kJ\, mol^{-1}$
  • $+ 4.3\, kJ\, mol^{-1}$
  • $- 4.3\, kJ\, mol^{-1}$
  • $- 8.6\, kJ\, mol^{-1}$
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The Correct Option is B

Solution and Explanation

Hydration energy of $NaCl = - 389.4 - 382.3$ $= -771.7\, kJ \,mol^{-1}$ $?H_{sol}. =$ Hydration energy - Lattice energy $= - 771.7 - (-776) = + 4.3 \,kJ \,mol^{-1}$
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Concepts Used:

Group 1 Elements

Group one of alkali metals is s-block elements with just one electron in their s-orbital. They are are alkali metals. They are named so because of the alkaline nature of the hydroxides and oxides.

Alkali metals are characterized by one s-electron in the valence shell of their atoms.

Alkali metals have a corresponding [Noble gas] ns1 electronic configuration. They occupy the first column of the periodic table. Alkali elements are:

  • Lithium(Li)
  • Sodium(Na)
  • Potassium (K)
  • Rubidium (Ru)
  • Cesium (Cs)
  • Francium (Fr)

They have occupied successive periods from first to seven. Francium is a radioactive element with very low half-life.

Electronic Configuration:

  • Alkali metals have one electron in their valence shell.
  • The electronic configuration is given by ns1. For example, the electronic configuration of lithium is given by 1ns1 2ns1.
  • They tend to lose the outer shell electron to form cations with charge +1 (monovalent ions).

This makes them the most electropositive elements and due to the same reason, they are not found in the pure state.