Jee mantra

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MOLE CONCEPT

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  • 1. JEE MANTRA MOLE CONCEPT

2. The concept of Atoms and Molecules Relative atomic mass of an element .Average mass per atom of the natural isotopic composition /1 /12 th mass of an atom of nuclide C-12 3. JEE MANTRA andRelative Atomic Mass Calculation BROMINE bromine consists of 50% 79Br and 50% 81Br, calculate the Ar of bromine. Ar = [ (50 x 79) + (50 x 81) ] /100 = 80 So the relative atomic mass of bromine is 80 or RAM or Ar(Br) = 80 Note the full working shown. Yes, ok, you can do it in your head BUT many students ignore the %'s and just average all the isotopic masses (mass numbers) given, in this case bromine -79 and bromine-81. 4. Relative molecular mass of the compound The ratio of average mass per molecule of the natural isotope to 1/12th mass of c-12, RMM (relative molecular mass)= sum of relative atomic masses of the atoms of molecule 5. Calculate the relative molecular mass of calcium hydroxide into the expression to find Mr( Ca3(PO4)3 (Ca2+)3(PO4 3-)2 or Ca3(PO4)3, but it makes no difference to the calculation of relative formula mass or relative molecular mass. atomic masses: Ca = 40, P = 31, O =16 RFM or Mr = (3 x 40) + 3 x {31 + (4 x 16)} = (120) + (3 x 95) = 405 6. Atomic mass unit The quantity 1/12th mass of an atom C-12 is known as atomic mass unit 1 amu=1.66 *10^-24 gramsgrams1.660 538 782(83) 1024g 1 gram of C- 12 = 6.02 x 10^23 amu The precise definition is that the atomic mass unit (u) is one twelfth of the mass of an isolated atom of carbon-12 (12C) at rest and in its ground state.[1] In other words, "A single atom of carbon-12 has a mass of 12 u exactly, by definition." 7. ATOMIC MASS The average mass per atom of natural isotopic composition is called atomic mass Atomic mass= Relative atomic mass x atomic mass unit 8. Molecular mass The average mass per molecule of natural isotopic composition of a compound is known as molecular mass Molecular mass= Relative molecular mass x atomic mass unit 9. Mole Mole= Wt in gm atom/atomic wt