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Q1. State the biological importance of Potassium?

Solution

Potassium ions are the most abundant cations within cell fluids. They even participate in the oxidation process of glucose to produce ATP. Sodium and potassium ions are responsible for the transmission of nerve signals. Also Na-K pump operates within the cell membrane.

Q2. What are the alkaline earth metals?

Solution

In periodic table, the elements of Group 2 include beryllium, magnesium, calcium, strontium, barium and radium. These elments with an exception of beryllium are commonly known as the alkaline earth metals. These are so called because their oxides and hydroxides are alkaline in nature and these metal oxides are found in the earth's crust.

Q3. Why does lithium show anomalous behavior?

Solution

Lithium differs in many respects from the remaining characteristic properties of the metals of Group 1, due to the following reasons:a) The size of lithium atom and ion is very small.b) The polarizing power of Li⁺ ion is quite high and results in the covalent character of its compounds.c) It has high ionization energy and least electropositive character.d) It has no vacant d-orbitals in its valence shell.

Q4. Why the group 1 elements are called alkali metals?

Solution

The hydroxide formed by these metals on reaction with water are strongly alkaline in nature, hence they are called alkali metals.

Q5. What is the common usefulness of alkali metals?

Solution

a) The chloride of sodium is used as common salt.b) Sodium is used in preparation of Borax.c) Potassium bromide is used in photography and in the manufacture of NPK fertilizers.d) The hydroxides of Potassium and sodium are used in manufacture of detergents.e) Rubidium and Francium are radioactive and used in chemical researches.f) Sodium and Potassium are the vital nutrients in human body. They help in Na- K pump.g) Sodium- bicarbonate is used in baking and is also called as baking powderh) Sodium compounds are also used as preservatives Ex:- MSG(monosodium glutamate).

Q6. Why does beryllium show anomalous behavior?

Solution

The properties of beryllium the first member of the alkaline earth metal, differ from the rest of the member. It is mainly because of(i) Its small size and high polarizing power.(ii) Relatively high electro negativity and ionization energy as compared to other members.(iii) Absence of vacant d - orbitals in its valence shell.

Q7. Explain the following (i) Alkaline earth metals are weaker reducing agent than alkali earth metals. (ii) Alkaline earth metals have higher melting point than alkali earth metals.

Solution

(i)     The reducing nature is determined by the tendency of losing electron. Since this tendency is lower in alkaline earth metal than alkali metal, the former are weaker reducing agent. (ii)   Due to the smaller size of alkaline earth metals as compared to alkali metals, alkaline earth metals have higher melting point than alkali earth metals.

Q8. When an alkali metal dissolves in liquid ammonia the solution can acquire different colors. Explain the reasons for this type of color change.

Solution

When alkali metals are dissolved in liquid ammonia they give blue colored conducting solution. This solution contain ammoniated electron which absorbs light in visible region and impart blue color to the solution. This solution is paramagnetic. In the concentrated solution the blue color changes to bronze color and solution becomes diamagnetic.

Q9. What is photoelectric effect?

Solution

When electromagnetic radiation strikes on the surface of alkali metals, they emit electrons. This is called the photoelectric effect. This occurs as alkali metals have low ionization energies, which allows the electrons to be easily ejected when exposed to light. Among alkali metals, cesium has lowest ionization energy and hence it can show photoelectric effect to the maximum extent.

Q10. Which element of group 2 is not known as alkaline earth metal?

Solution

The element of group 2 is not known as alkaline earth metal is Beryllium.

Q11. Solvay process cannot be used for preparing potassium carbonate. Why?

Solution

Solvay process cannot be used for preparing potassium carbonate because when ammonium hydrogen carbonate is added to a saturated solution of KCl, the potassium hydrogen carbonate formed is soluble and do not precipitate out like sodium hydrogen carbonate.

Q12. MgCl₂ and CaCl₂ exist as MgCl₂.6H₂O and CaCl₂· 6H₂O while NaCl and KCl do not form such hydrates. Why?

Solution

Because the hydration enthalpies of alkaline earth metal ions, they are larger than those of alkali metal ions. Hence, NaCl and KCl do not form such hydrates as MgCl₂ and CaCl_2.

Q13. Why the second ionization enthalpies of alkaline earth metals are lower than alkali metals?

Solution

The removal of second electron from alkaline earth metals leads to the stable octet state in M²⁺ ions. In case of alkali metals it is not so. Since the removal of electron leads to stability, hence it can easily removed leading to lowering of second ionization enthalpy in alkaline earth metals.

Q14. State any two uses of washing soda.

Solution

Washing soda is used: 1. In paper, paints and textile industries. 2. In the manufacture of glass, soap, borax and caustic soda.

Q15. Why are potassium and caesium, rather than lithium used in photoelectric cells?

Solution

Because of low ionization enthalpy of potassium and caesium as compared to lithium, they are able to lose their outermost electron when exposed or irradiated with light. This property makes caesium and potassium useful in photoelectric cells.

Q16. Explain why is sodium less reactive than potassium?

Solution

The reactivity of alkali metals are due to their large size and low ionization enthalpy which in turn eases the loose of outermost electrons of alkali metals. As we go down the group the size of metal increases and ionization enthalpy decreases. This is the reason sodium is less reactive than potassium.

Q17. Give the name of radioactive alkali metal.

Solution

The name of a radioactive alkali metal is Francium, ²²³Fr.

Q18. Write down the electronic configuration of Ba.

Solution

The electronic configuration of Ba(56) is 1s²2s²2p⁶3s²3p⁶3d¹⁰4s² 4p⁶4d¹⁰5s²5p⁶6s².

Q19. What are alkali metals? Give the name of the elements.

Solution

The six elements belonging to group 1 of the periodic table, namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr) are called alkali metals. They constitute alkali metals because they readily dissolve in water to form hydroxides, which are strongly alkaline in nature.

Q20. Why the Mg and Be reacts with air only in powdered state?

Solution

Due to formation of an oxide film on the surface of metal they are unable to react further. Hence powdered metal is used to react with air.

Q21. Beryllium and magnesium do not give color to flame whereas other alkaline earth metals do so. Why?

Solution

Generally the colour of flame of alkaline metals are due to the  reason that electrons are excited to higher energy levels and when they drop back to the ground state, energy is emitted in the form of visible light. Since the electrons in beryllium and magnesium are too strongly bound it cannot get excited by flame. Hence Beryllium and magnesium do not give color to flame.

Q22. Give the name of rarest alkaline earth metal found in igneous rocks.

Solution

The name of the rarest alkaline earth metal found in igneous rocks is Radium.

Q23. Why alkali metals are kept in kerosene oil?

Solution

Because of the high reactivity of alkali metals they are kept in kerosene oil.

Q24. Why Sr(OH)₂ and Ba(OH)₂ are soluble in water whereas Be(OH)₂ and Mg(OH)₂  are almost insoluble in water?

Solution

Be(OH)₂ and Mg(OH)₂ are almost insoluble, Ca(OH)₂ is sparingly soluble while Sr(OH)₂ and Ba(OH)₂ are fairly soluble. This is due to increase in size of the cation and decrease in their lattice energies on moving down the group. Hydration energies become more due to decrease in lattice energies and so the solubility of hydroxide in water increases. This explains the increasing solubility of alkaline Earth metal hydroxides on moving down the group. Lattice energy decreases with increase in size of the cation and therefore, solubility increases from Be to Ba.

Q25. Name the elements pair of s-block which show diagonal relationship.

Solution

The elements pair of s-block which show diagonal relationship are as follows: Lithium-Magnesium, Beryllium-Aluminium.

Q26. Give the name of most and least powerful reducing agent among alkali metals.

Solution

Lithium is the most powerful and sodium is the least powerful reducing agent among alkali metals.

Q27. Why the group 2 elements are called alkaline earth metals?

Solution

Because the oxides and hydroxide formed by these metals are strongly alkaline in nature and these metal oxides are found in earth crust.

Q28. What are the features of lithium which separates it from other elements of Group 1?

Solution

The following features separate lithium from the other elements of Group I: (i) Lithium is the hardest of all the alkali metals.(ii) The melting and boiling points of lithium are much higher than those of other elements of Group 1.(iii) Lithium is less reactive as compared to other metals and it does not get tarnished readily in air.(iv) It forms only monoxide, Li₂O with oxygen while sodium forms peroxide-Na₂O₂; other elements form superoxide, MO₂.(v) Because of high polarizing power of Li⁺ ion, the salts of lithium have lower ionic character than salts of other alkali metals.(vi) While other alkali metals do not react with nitrogen, lithium does, forming nitride.(vii) Only lithium combines with carbon and silicon forming the carbide and the silicide.(viii) Lithium hydroxide and carbonate are unstable and decompose on heating while the corresponding compounds of the rest of the family members are stable and do not decompose:(ix) When lithium nitrate is heated it gives nitrogen dioxide and oxygen(x) Sodium nitrate and potassium nitrate upon strong heating form corresponding nitrites and evolve oxygen.(xi) Lithium chloride and nitrate are soluble in alcohol, while the salts of sodium are insoluble in alcohol.(xii) The hydride of lithium (LiH) is more stable as compared to the hydrides of other members of the family.(xiii) The Li+ ion and its compounds are more heavily hydrated than those of sodium.(xiv) Lithium hydroxide is much less basic than the hydroxides of other metals.(xv) Lithium fluoride, carbonate, hydroxide, oxalate are sparingly soluble in water. The corresponding salts of sodium and potassium are readily soluble.

Q29. Why is LiF almost insoluble in water whereas LiCl soluble not only in water but also in acetone?

Solution

Due to high lattice enthalpy of LiF as compared to LiCl, LiF is almost insoluble in water. LiCl is soluble in acetone also due to larger anion as compared to cation, polarization occur and thus LiCl posses some covalent character.

Q30. Discuss any four properties which show the anomalous behavior of Be and its similarity with Al.

Solution

The following points illustrate the anomalous behavior of Be and its resemblance with Al.(i) Unlike groups - 2 elements but like aluminium, beryllium forms covalent compounds.(ii) The hydroxides of Be, [Be(OH)₂] and aluminium [Al(OH)₃] are amphoteric in nature, whereas those of other elements of group - 2 are basic in nature.(iii) The oxides of both Be and Al i.e. BeO and Al₂O₃ are high melting insoluble solids.(iv) BeCl₂ and AlCl₃ have bridged chloride polymeric structure.