Short Answer TypeStarting with CaCO3, write balanced chemical equation showing the preparation of:
(i) CaO (ii) CaSO4 (iii) Ca(OH)2 (iv) Ca(HCO3)2 solution.
Long Answer TypeDescribe two important uses of the following;
(a) Caustic soda (b) Sodium carbonate (iii) Quick lime.
What happens when,
(i) magnesium is burnt in air
(ii) quick- lime is heated with silica
(iii) chlorine reacts with slaked lime
(iv) calcium nitrate is heated?
Discuss the composition and manufacturing details of cement.
Or
Mention the main constituents of Portland cement.
Short Answer TypeContrast the action of heat on the following and explain your answer:
(i) Na2CO3 and CaCO3
(ii) MgCl2.6H2O and CaCl2.6H2O
(iii) Ca(NO3)2 and NaNO3.
What are the common physical and chemical features of alkali metals?
Physical properties:
i) metallic character: Alkali metals are highly electropositive in nature and hence, they are typical metals. the metallic character is due to low values of ionisation energies and consequently, they have a tendency to lose the valence electrons.
Low ionisation energy: The first ionisation energies of alkali metals are quite low as compared to the elements of the other groups belonging to the same period. the reason is that atoms of alkali metals are of large sizes. Therefore, the outermost electron is far away from the nucleus and can be easily removed. Within the group, ionisation energies of alkali metals decrease as we move down the group.
Low melting and boiling point: The melting and boiling points of alkali metals are very low because of the large size of their atoms due to which inter-particle forces are very weak in them. The melting and boiling points decrease on going down the group(Lithium to Cesium) as the charge density decreases because of the increase in the size of the monovalent cation.
Low electronegativity: Alkali metals have low values of electronegativity. They have very little tendency to attract the shared pair of electrons towards themselves. The electronegativity values of alkali metals decrease as we move down in the group from Li to Cs.
Soft in nature: All the alkali metals are soft and can be cut with the help of a knife.The softness of alkali metals is due to weak metallic bonding in them as the result of the large size of the atoms. As we move down the group, metallic bonding weakens and therefore, softness increases.
Density: Alkali metals have low density due to the large size of metals atoms.
Oxidation state: The alkali metals exhibit oxidation state of +1 in their compounds and strongly electropositive in character. the electropositive character increases from lithium down to caesium in the group.
Chemical properties:
Decomposition of water: The alkali metals decompose water at the ordinary temperature giving out hydrogen.
2Li+2H2O --> 2LiOH +H2
2Na +2H2O --> 2NaOH + H2
2K +2H2O --> 2KOH +H2
Reaction with oxygen: The alkali metals readily burn in oxygen or air to form their oxides
4Li +O2 -->2LiO
combination with halogens: The alkali metals burns in halogens forming their halides
2Na +Cl2 --> 2NaCl
Discuss the general characteristics and gradation in properties of alkaline earth metals.
Compare the alkali metals and alkaline earth metals with respect to (i) ionisation enthalpy (ii) basicity of oxides and (iii) solubility of hydroxides.
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