Ncert Solutions Chemistry Class 12th
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6 months agoContributor-Level 10
8.37 An alloy is a homogenous mixture of two or more metals or non-metals. Lanthanoid is used for the production of alloy steels for plates and pipes called as mischmetals. It contains about 95% lanthanoid metal, iron and traces of Al, S, C etc. in traces. It is used in magnesium- based alloy to produce bullets, shells and lighter flint.
New answer posted
6 months agoContributor-Level 10
8.36 (i) The chromite ore (FeCr2O4) is fused with sodium hydroxide (NaOH)
4FeCr2O4 +16 NaOH+ 7O2 → 8Na2CrO4 +2Fe2O3 +8H2O
The yellow solution of sodium chromate is then filtered and acidified with sulphuric acid giving its dichromate.
2Na2CrO4 +H2SO4→ Na2Cr2O7 + Na2SO4 +H2O
On cooling, sodium sulphate crystallizes out as Na2SO4.10H2O and is removed.
Na2Cr2O7 +2KCl → K2Cr2O7 + 2NaCl
(ii) The pyrolusite ore(MnO2) is oxidised in the presence of potassium hydroxide by heating.
2MnO2 + 4KOH +O2→ 2K2MnO4 + 2H2O
The green potassium manganate (K2MnO4) is then treated with a current of chlorine or ozone to oxidise potassium manganate to potassi
New answer posted
6 months agoContributor-Level 10
8.35 (i) The lower oxide have low oxidation state while the higher oxide has high oxidation state, example MnO is basic and Mn2O7 is
(ii) Oxygen and fluorine have a small size and high electronegativity and can easily oxidize metals, example V2O5.
(iii) Oxoanions of metals have higher oxidation states because of high electronegativity of oxygen and highly oxidizing property example, Cr in CrO7 2- has an oxidation state of +6
New answer posted
6 months agoContributor-Level 10
8.34 From the table given below:
Mn3+ : 3d4 | unpaired electrons = 4 |
V3+ : 3d2 | unpaired electrons =2 |
Cr3+ : 3d3 | unpaired electrons= 3 |
Ti3+ : 3d1 | unpaired electrons =1 |
Cr3+ is most stable in aqueous solution because of half filled d-orbital.
New answer posted
6 months agoContributor-Level 10
8.33 Copper (29) has electronic configuration 1s22s22p63s23p63d104s1. It can easily lose one electron to give stable configuration as it has completely filled d-orbital.
New answer posted
6 months agoContributor-Level 10
8.32 The reactions in which same substance gets oxidized as well as reduced due to unstable oxidation state.
Example:
2MnO42- + 4H+? 2MnO4- + MnO2 + 2H2O
Mn (VI) is oxidised to Mn (VII) and also reduced to Mn (IV).
2CrO4 3- +2H+? CrO4 2- +Cr3+ + 4H2O
Cr (V) is oxidised to Cr (VI) and also reduced to Cr (III).
New answer posted
6 months agoContributor-Level 10
8.31 (i) Of the d4 species, Cr2+ is strongly reducing while manganese (III) is strongly oxidizing: The +2 oxidation state becomes more stable on moving across a period i.e. the tendency of metals to give electrons becomes more. Therefore, vanadium(II) oxide and chromium(II) oxide are strong reducing agents.
As if the value of electrode potential is higher i.e. more energy required to withdraw an electron from an isolated atom, more readily it can be reduced and lesser the electrode potential more readily it can be oxidized.
The electrode potential of Cr3+? Cr2+is negative so it acts reducing agent or can undergo oxidation which makes it
New answer posted
6 months agoContributor-Level 10
8.30
| Lanthanoids | Actinoids |
Electronic Configuration | It is represented by [Xe]4fx5dy6s2, where x varies from 0 to 14 and y= 0 or 1 | It is represented by [Rn]5fx6dy7s2, where x varies from 0 to 14 and y= 0 or 1. |
Oxidation state | Generally shows +3 oxidation state only in some cases it is +2 or +4 but never greater than +4 | It has +3 oxidation state but also shows higher oxidation states such as +4, +5, +6, +7. |
Atomic and ionic sizes | Ionic radii of M3+ions decrease in size with increase in atomic number this is called as lanthanoid contraction. | There is a gradual decrease in the size of M3+ ions across the series, this is known as actinoid contraction. |
Chemical Reactivity | Lanthanoids are less reactive in nature and form oxides, sulphides, nitrides etc. They have a lesser tendency to form complexes. | They are highly reactive in nature when they are in the finely divided state. They have a higher tendency to form complexes and even react with non-metals at moderate temperature. |
Actinoid Contraction > Lanthanoid contraction
Lanthanoids show lanthanoid contraction due to which their size is quite small as compared to actinoids although there is actinoid contraction also lanthanoid contraction has more impact on elements as there is one shell less than actinoids, so lanthanoids have less tendency to lose an electron and to undergo any reaction like the formation of oxide etc.
New answer posted
6 months agoContributor-Level 10
8.29 It can be observed from the above table that in the starting of 3d transition series elements like Sc, Ti, V, Cr in +2 state are not that stable in their elements in the +3 state.
In the middle Mn2+, Fe2+, Co2+are quite known. In fact, Mn2+ and Mn7+ are most stable states in Mn. Fe2+ is less stable when compared to Fe3+ which is due to fact that Fe3+ is able to loose one electron to acquire d5 state which has extra stability. Co2+ is less stable as compared to Co3+.
Ni2+ is the most common and stable among its +2, +3, +4 states. Cu2+ is more stable and is quite common as compared to Cu+. Towards the end, Zn forms only Zn2+ whic
New answer posted
6 months agoContributor-Level 10
8.28 Metal ions which have valence electrons in d-orbital and in which d-d transition can take place will be coloured and the metal ions which have completely filled orbital or have d- orbital will be colourless as no d-d transition is possible in those configurations.
Element | Atomic Number | Ionic State | Electronic configuration in ionic state |
Ti | 22 | Ti3+ | [Ar] 3d1 |
V | 23 | V3+ | [Ar] 3d2 |
Cu | 29 | Cu+ | [Ar] 3d10 |
Sc | 21 | Sc3+ | [Ar] |
Mn | 25 | Mn2+ | [Ar] 3d5 |
Fe | 26 | Fe3+ | [Ar] 3d5 |
Co | 27 | Co2+ | [Ar] 3d7 |
From the above table, it can be observed that only Sc3+ and Cu+ have either completely filled d- orbital or empty d-orbital. So, all other ions except Sc3+ and Cu+ will be coloured in aqueous solution because of absorption of radiations which fall in the visible region as on obtaining energy electrons jump from one d-orbital to another.
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