Hydrogen and s Block Elements Terminal Questions with Answer NIOS
National Institute of Open Schooling (NIOS)
Sr. Secondary, Module-6
Lession-17: Hydrogen and s Block Elements Terminal Questions with Answer
Terminal QUESTIONS
1. Write three general characteristics of the s-block elements which distinguish them from the elements of other blocks.
Answer:General characteristics of the s-block elements which distinguish them from the elements of other blocks are-
1.The s-block elements have an outer electronic configuration ns1 or ns2
2.Alkali metal is weak in its metallic bonding and so they are having low boiling and melting points.
3.They have low values of ionisation energies and are hence highly electropositive.
4. They have the largest atomic radii in their corresporiding periods.
2. The alkali metals follow the noble gases in their atomic structure. What properties of these metals can be predicted from this information?
Answer:It can be predicted that they are electropositive and have low values of ionization energy.
3. What happens when?
a. sodium metal is dropped in water.
b. sodium metal is heated in free supply of air.
c. sodium peroxide dissolves in water.
Answer:a. Sodium metal reacts rapidly with water to form a colourless basic solution of sodium hydroxide and hydrogen gas. The reaction is very exothermic.
2Na + 2H2O → NaOH + H2
b. If Na metal is heateed in the presence of free supply of air it forms sodium peroxide and also forms sodium oxide in small quantity.
Na2O + 1/2 O2 → Na2O2 (major product)
4Na + O2 → 2Na2O (minor product)
c. When sodium peroxides are dissolved in water hydrogen peroxides are formed along with the sodium hydroxide.
Na2O2 + 2H2O → 2NaOH + H2O2
4. Explain why hydrogen is best placed separately in the periodic table of elements.
Answer:Hydrogen behaves both like alkali metals and halogens. That's why hydrogen is best placed separately in the periodic table.
5. Describe the industrial applications of hydrogen.
Answer:Industrial applications of hydrogen are-
1. Chemical industries uses hydrogen for the synthesis of plastics, polyester and nylon.
2. As a primary fuel for heavy rockets.
3. Hydrogen is used in nuclear reactors. Deuterium is used in the field of nuclear fission, as a moderator to slow down neutrons, and also in nuclear fusion reactions.
4. In Hydrochloric acid and Ammonia production. Hydrogen reacts with chlorine to form HCI, and with nitrogen to form ammonia.
5. In the hydrogenation of oils. Vegetable oils change in to vegetable ghee when hydrogen is passed through the oils at 443K in presence of nickel as catalyst.
6.Hydrogen is used to make methanol or methyl alcohol that is used as antifreezing agent, solvent and fuel.
6. Discuss the importance of heavy water in nuclear reactor and how is it prepared from normal water?
Answer:Heavy water is used as a moderator in nuclear reactors because it slows down the fast moving neutrons and therefore helps in controlling the nuclear fission process so that they are more likely to react with the fissile uranium-235 than with uranium-238, which captures neutrons without fissioning. Heavy water is separated from normal water by electrolysis. In order to obtain one litre of almost pure heavy water, we have to electrolyze about 30000 litres of ordinary water.
7. Name the isotopes of hydrogen. What is the importance of heavier isotopes of hydrogen?
Answer:Naturally occurring hydrogen contains three isotopes- Protium 1H1 or H, Deuterium 1H2 or D and Tritium 1H3 or T. The heavier isotopes of hydrogen brings out the nuclear properties of water. Increase in the mass of the water due to deuterium makes the water slightly different from normal water in terms of physical and chemical properties.
8. Why is ice less dense than water and what kind of attractive forces must be overcome to melt ice?
Answer:Ice is less dense than water because of its porous or cage like structure. The intramolecular forces that have to overcome during the melting ice are dispersion, dipole-dipole interaction and hydrogen bond.
9. Show by proper chemical reactions how hydrogen peroxide can function both as an oxidizing and a reducing agent?
Answer:A. Chemical reactions justifying oxidizing nature of H2O2 are as follws-
H2O2 + 2KI → 2KOH + I2
Hg + H2O2 → HgO + H2O
B. Chemical reactions that justify the reducing nature of H2O2 are as follows-
H2O2 + C l 2 → 2HCl + O2
PbO2 + H2O2 → PbO + H2O + O2
10. Compare the properties of alkali metals and alkaline earth metals with respect to:
a. atomic radii
b. ionization energy
c. melting points
d. reducing behavior
Answer:a. Atomic Radii: Atomic Radii of alkali metals are larger than that of alkaline earth metals.
b. Ionization Energy: Ionization energy of alkali metals are lower than alkaline earth metals.
c. Melting Points: Alkaline earth metals have higher melting points.
d. Reducing Behavior: Alkaline earth metals are poor reducing agents as compared to alkali metals.
11. Explain the trends of solubility and stability of the carbonates and sulphates of alkaline earth metals.
Answer:Solubility: BeCO3 > MgCO3 > CaCO3 > SrCO3 > BaCO3
BeSO4 > MgSO4 > CaSO4 > SrSO4
Stability: BeCO3 < MgCO3 < CaCO3 < SrCO3 < BaCO3
BeSO4 < MgSO4 < CaSO4 < SrSO4
12. Explain the process involved in the manufacture of NaOH, Na2CO3 and NaHCO3 (Give Chemical equations only).
Answer:Reactions involving in manufacturing of NaOH Castner-Kellner cell:
Ionization of brine solution
2NaCl → 2Na+ + 2Cl-
Reaction at the anode:
2Cl- → Cl2 + 2e-
Reaction at the cathode:
2Na+ + 2e- → 2Na
The amalgam formed is treated with water to obtain a sodium hydroxide solution. On evaporation of the solution, solid sodium hydroxide is formed.
Na2CO3
1. 2NH3 + H2O + CO2 → (NH4)2CO3
2. (NH4)2CO3 + H2O + CO2 → 2NH4HCO3
3. NH4HCO3 + NaCl → NH4Cl + NaHCO3
4. 2NaHCO3 → Na2CO3 + CO2 + H2O
The amalgam formed is treated with water to obtain a sodium hydroxide solution.On evaporation of the solution, solid sodium hydroxide is formed.
NaHCO3
CO2 + H2O + NH3 + NaCl → NaHCO3 + NH4Cl
NaHCO3 → Na2CO3 + CO2 + H2O
Carbon dioxide produced is recycled to produce NaHCO3
13. Explain the biological role of Ca2+ and Mg2+.
Answer:biological role of Ca2+ ion-
a. Ca+2 is present in bones and teeth as apatite Ca3(PO4)2. Enamel on teeth is flour apatite.
b. It is necessary for blood clotting.
c. Ca+2 ions are necessary to maintain heart beating.
d. Ca+2 ions are necessary for muscle contraction.
biological role of Mg2+ ion-
a. Mg+2 are concentrated in animal cells.
b. Enzymes like ‘phosphohydrolyses’ and ‘phosphotransferases’ contain Mg+2 ions. These enzymes participate in ATP reactions and release energy in the process.
c. Mg+2 is constituent of chlorophyll.
