as chemistry amount of substance

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ghoran
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243306
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as chemistry amount of substance
Updated:
2013-10-28 03:44:08
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  1. moles =
    • ----------
    • Ar or Mr 

    or 

    • cm^3 x M
    • -------------
    •    1000
  2. percentage purity =
    • mass of pure substance x 100
    • ..........................................
    • mass of impure substance
  3. a fertiliser contains ammonium sulphate and potassium sulphate . when 0.5g of the fertliser was warmed up with sodium hydroxide solution , ammonia gas was evolved . the ammonia required 15cm^3 of 0.2M hydrochloric acid to neutralise it . what is the percentage by mass of ammonium sulphate in the fertiliser ?
    • (NH4)2SO4 + 2NaOH-2NH3 + NA2SO4 + 2H20
    • NH3 + HCL - NH4CL

    • work out moles of HCl 
    • moles = 15 x 0.2/1000 = 0.003
    • so moles of NH3 = 0.003 in equation 1 
    • moles of (NH4)2SO4 in equation 2 = 0.003/2 = 0.0015 
    • mass of (NH4)SO2 moles = mass/mr 
    • 0.0015 = x/132 
    • 0.0015 x 132 = x = 0.198 g 
    • percentage of ammonium sulphate =
    • mass of ammonium sulphate 
    • -------------------------------- x 100 
    • mass of fertliser 
    • 0.198
    • -------- x 100 = 39.6%
    • 0.50
  4. atom economy
    the percentage of the starting materials used in a reaction that are incorporated into the useful products
  5. % atom economy =
    • mass of desired products 
    • .................................. x 100
    • total mass of reactants
  6. % yield =
    • number of moles of specified product 
    • ................................................... x100
    • theoretical maximum number of moles 
    •                of the product 

    or 

    • mass of product obtained 
    • ------------------------------ x 100 
    • theoretical maximum mass 
    •        of the product

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