The Total solution for NCERT class 6-12
Answer - 21 : -
Answer - 22 : -
(i)Al reacts with cone. HNO3 toform a very thin film of aluminium oxide on its surface which protects it fromfurther reaction.2Al(s) + 6HNO3(conc.)———> Al2O3(s) + 6NO2(g) + 3H2O(l)(ii) NaOH reacts with Al to evolve H2 gas. Thus the pressure of the gas produced can beused for clogged drains.2Al(s) + 2NaOH(aq) + 2H2O(l)——-> 2NaAlO2(aq) +3H2(g)(iii) Graphite has layered structure which are held by weak van der Waalsforces. Thus, graphite cleaves easily between the layers, therefore it is verysoft and slippery. That’s why it is used as lubricant.(iv) Diamond is used as an-abrasive because it is an extremely hard substance.(v) Alloys of aluminium, like duralumin, is used to make aircraft body due tosome of its property like toughness, lightness and resistant to corrosion.(vi) Generally, aluminium metal does not react with water quickly but, when itis kept overnight, it reacts slowly with water in presence of air.2Al(s) + O2(g) + H2O(l) ——–> Al2O3(S) + H2(g)a very small amount of (in ppm) Al3+ producedin the solution is injurious to health if the water is used for drinkingpurposes.(vii) Aluminium is generally unaffected by air and moisture and it is also goodconductor of electricity. That’s why it is used in transmission cables.
Answer - 23 : -
Becausethere is increase in atomic size on moving from carbon to silicon, thescreening effect increases. Thus the force of attraction of nucleus for thevalence electron decreases as compared to carbon. Thus the ionization enthapydecreases from carbon to silicon.
Answer - 24 : -
Dueto poor shielding effect of d-electrons in Ga, the electrons in galliumexperience great force of attraction by nucleus as compared to Al.
Answer - 25 : - Allotropes: Allotropes arethe different forms of an element which are having same chemical properties butdifferent physical properties due to their structures.
Indiamond, carbon is SP3 -hybridized.Since, diamond is three dimensional network solid, it is hardest substance withhigh density whereas graphite has a layered structure. The various layers areformed by van der Waals forces of attraction that’s why graphite is soft andslippery.
Answer - 26 : - (a) Neutral — COAcidic — B2O2, Si02, C02 Basic — Tl2O3 Amphoteric — Tl2O3,PbO2(b)-CO does not react with acid as well as base at room temperature.Being acidic B2O3, Si02 and C02 reacts with alkalisto form salts.
Answer - 27 : -
Tlshows both the oxidation state +1 and +3 due to inert pair effect. Tl formsbasic oxide like group I elements. TlO2 is strongly basic.
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Answer - 29 : -
(a) Inert pair effect: The pair ofelectron in the valence shell does not take part in bond formation is calledinert pair effect.(b)Allotropy: Itis the property of the element by which an element can exist in two or moreforms which have same chemical properties but different physical properties dueto their structures.(c)Catenation: Theproperty to form chains or rings not only with single bonds but also withmultiple bonds with itself is called catenation.For example, carbon forms chains with (C-C) single bonds and also with multiplebonds (C = C or C = C).
Answer - 30 : -