class 11 chemistry notes

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Preparation and properties of Borax

Preparation             Borax occurs naturally as tincal(contains about 55% borax) in certain inland lakes of India, Tibet andCalifornia (U.S.A.).             Borax can also be prepared from certain other minerals such as boracite, colemanite and boranatrocalcite. The minerals are powdered and boiled with sodium carbonate solution.                      Ca 2 B 6 O 11   +   2Na 2 CO 3 ¾ ®     2CaCO 3   +   Na 2 B 4 O 7   +   2NaBO 2             Borax is crystallised from the filtrate. Sodium metaborate, present in the mother liquor, is converted into borax by passing carbon dioxide through it            ...
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Silicates Notes for class 11 Chemistry

class 11 chemistry Notes Silicates Binary compounds of silicon with oxygen are called silicates but they contain other metals also in their structures. (i)              Since the electronegativity difference between O & Si is about 1.7, so Si–O bond can be considered 50% ionic & 50% covalent. (ii)            If we calculate the radius ratio then,r Si 4+ /r O 2- = 0.29 It suggests that the coordination number of silicon must be 4 and from VBT point of view we can say that Si is sp 3   hybridized. Therefore silicate structures must be based upon SiO 4 4–   tetrahedral units. (iii)       SiO 4 4–   tetrahedral units may exist as discrete units or may polymerise into larger units by sharing corners.         ...
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Isolation of Boron class 11 chemistry Notes

Isolationof Boron   Ores of boron             (i)   Borax or tincal : Na 2 B 4 O 7 .10 H 2 O               (ii) Kernit or Rasorite : Na 2 B 4 O 7 . 4 H 2 O             (iii) Colemanite : Ca 2 B 6 O 11 . 5 H 2 O             (iv) Orthoboric acid : H 3 BO 3   (It occurs in the jets of steam called soffioni escaping from ground in the volcanic region of the Tuscany ). Boron is present to a very small extent (0.001%) in earth’s crust. (i)         Reduction of boric oxide with highly electropositive metals like Na, K and Mg in the absence of                 ...
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