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Post a LessonAnswered on 10 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Sadika
Oxidation State of Sodium in Na2O2: In Na2O2Na2O2, each oxygen atom is in the peroxide ion (O22−O22−). Since the overall charge of the compound is 0, sodium must be in the +1 oxidation state to balance the negative charges from the peroxide ions. So, the oxidation state of sodium in Na2O2Na2O2 is +1.
read lessAnswered on 13 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Nazia Khanum
Potassium and cesium are sometimes preferred over lithium in photoelectric cells due to their lower ionization energy. Ionization energy is the energy required to remove an electron from an atom or ion in its gaseous state. Both potassium and cesium have lower ionization energies compared to lithium, making it easier to liberate electrons from their surfaces when exposed to light.
In photoelectric cells, the goal is to efficiently convert light energy into electrical energy by causing the emission of electrons from a material's surface (the photoelectric effect). Materials with lower ionization energies can release electrons more readily when illuminated by photons, leading to a more efficient conversion process.
However, the choice of material also depends on various factors such as cost, stability, and practical considerations in the specific application. While potassium and cesium may have advantages in certain cases, lithium could still be chosen for other applications where its properties are more suitable.
Answered on 13 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Nazia Khanum
When alkali metals like lithium, sodium, or potassium dissolve in liquid ammonia, they form solutions that exhibit interesting color changes. This phenomenon is due to the formation of solvated electrons, which are free-moving electrons surrounded by a shell of solvent molecules (in this case, ammonia molecules).
Initially, as the alkali metal dissolves, the solution appears blue due to the presence of solvated electrons. These solvated electrons are responsible for the blue coloration. However, as more metal dissolves and the concentration of solvated electrons increases, the color of the solution changes to bronze, gold, or even reddish-brown.
This change in color occurs because as the concentration of solvated electrons increases, they begin to interact with each other, forming dimers and other aggregates. These aggregates absorb light differently, leading to a change in the observed color of the solution. The exact color observed depends on factors such as the concentration of solvated electrons and the specific alkali metal involved.
Overall, the color changes observed in alkali metal solutions in liquid ammonia are due to the formation of solvated electrons and their subsequent interactions, which alter the absorption properties of the solution.
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Answered on 29 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Deepika Agrawal
"Balancing minds, one ledger at a time." "Counting on expertise to balance your knowledge."
Answered on 29 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Deepika Agrawal
"Balancing minds, one ledger at a time." "Counting on expertise to balance your knowledge."
Answered on 29 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Deepika Agrawal
"Balancing minds, one ledger at a time." "Counting on expertise to balance your knowledge."
Different concentrations of alkali metals in liquid ammonia results in different colours. The dilute solutions are blue in colour due to presence of ammoniated electrons. The concentrated solutions have copper bronze colour as ammoniated metal ions are bound by free electrons.
read lessTake Class 12 Tuition from the Best Tutors
Answered on 29 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Deepika Agrawal
"Balancing minds, one ledger at a time." "Counting on expertise to balance your knowledge."
Answered on 29 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Deepika Agrawal
"Balancing minds, one ledger at a time." "Counting on expertise to balance your knowledge."
Answered on 29 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Deepika Agrawal
"Balancing minds, one ledger at a time." "Counting on expertise to balance your knowledge."
Take Class 12 Tuition from the Best Tutors
Answered on 29 Apr Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals)
Deepika Agrawal
"Balancing minds, one ledger at a time." "Counting on expertise to balance your knowledge."
(a) On moving down the alkali group, the ionic and atomic sizes of the metals increase. The given alkali metal ions can be arranged in the increasing order of their ionic sizes as:
Li+ < Na+ < K+ < Rb+ < Cs+
Smaller the size of an ion, the more highly is it hydrated. Since Li+ is the smallest, it gets heavily hydrated in an aqueous solution. On the other hand, Cs+ is the largest and so it is the least hydrated. The given alkali metal ions can be arranged in the decreasing order of their hydrations as:
Li+ > Na+ > K+ > Rb+ > Cs+
Greater the mass of a hydrated ion, the lower is its ionic mobility. Therefore, hydrated Li+ is the least mobile and hydrated Cs+ is the most mobile. Thus, the given alkali metal ions can be arranged in the increasing order of their mobilities as:
Li+ < Na+ < K+ < Rb+ < Cs+
(b) Unlike the other elements of group 1, Li reacts directly with nitrogen to form lithium nitride. This is because Li+ is very small in size and so its size is the most compatible with the N3– ion. Hence, the lattice energy released is very high. This energy also overcomes the high amount of energy required for the formation of the N3– ion.
(c) Electrode potential (E°) of any M2+/M electrode depends upon three factors:
(i) Ionisation enthalpy
(ii) Enthalpy of hydration
(iii) Enthalpy of vaporisation
The combined effect of these factors is approximately the same for Ca, Sr, and Ba. Hence, their electrode potentials are nearly constant.
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