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. ...
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 ...
Trigonometry The Word 'trigonometry' is derived from the Greek words 'tri' (meaning tree), 'gon' (meaning sides) and 'metron' (meaning measure). In fact trigonometry is the study of relationship between the sides and angle o the triangle. In This chapter, we will study some ration of the sides of a right triangle with respect to its acute angles, called trigonometric ratios of the angle. We will restrict our discussion to acute angle only. However, these ratios can be extended to other angles also. We will also define the trigonometric rations for angles of measure 0 o and 90 o . We will calculate trigonometric ratios for some specific angles and establish some identities involving these rations, called trigonometric identities. Trigonometricration Let us take a right triangle ABC as shown in Here CAB (or, in brief, angle A) is an acute angle. Note the position of the side BC with respect to angle A. If faces A. we ca...
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