# as chemistry amount of substance

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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
 Author: ghoran ID: 243306 Card Set: as chemistry amount of substance Updated: 2013-10-28 07:44:08 Tags: unit Folders: Description: revision Show Answers: