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Oxidising Ability of Concentrated Sulphuric Acid

This module explores the reactions of concentrated sulphuric acid with halide ions in aqueous solutions during the formation of hydrogen halides. It also discusses the oxidising ability of concentrated sulphuric acid.

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Oxidising Ability of Concentrated Sulphuric Acid

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  1. Welcome and thanks for visiting. Module 3 Practical: Structured Questions 2002-7 NaClFind LEf F Scullion. JustChemy.Com

  2. 2004/P1

  3. 2004/P2

  4. 2005/P1

  5. 2005/P2

  6. Full explanation provided on the next slide

  7. Oxidising ability of Concentrated Sulphuric Acid.Its reactions with halide ions in aqueous solution during the formation of the Hydrogen Halides. [CARE: CARRY OUT ALL OF THESE IN A FUME CUPBOARD WITH GREAT CARE] 2a)   KBr(s)     +     H2SO4(l)     KHSO4(aq)   +      HBr(g) However, the concentrated sulphuric acid will oxidise some of the HBr as follows: -1 0 2b)    2HBr    +      H2SO4      Br2    +      SO2   +      2H2O Therefore, one will observe a Reddish Vapour due to some bromine being present. The SO2 is and acidic gas. It is also a reducing agent and will, for example, decolourise purple potassium permanganate solution An increase in O.N.

  8. SUMMARY for all of the Halides.Oxidising ability of Concentrated Sulphuric Acid.Its reactions with halide ions in aqueous solution during the formation of the Hydrogen Halides. [CARE: CARRY OUT ALL OF THESE IN A FUME CUPBOARD WITH GREAT CARE] 1)     NaCl(s)     +      H2SO4(l)      =      NaHSO4(aq)  +   HCl(g) The concentrated sulphuric acid will not oxidise HCl 2a)    KBr(s)       +      H2SO4(l)      =      KHSO4(aq)   +      HBr(g) The concentrated sulphuric acid will oxidise some of the HBr as follows:      2b)    2HBr    +         H2SO4        +    Br2    +      SO2   +      2H2O Therefore, one will observe a Reddish Vapour  due to some bromine being present.    3a)    KI(s)          +    H2SO4(l)    à     KHSO4       +      HI(g) The concentrated sulphuric acid will oxidise some of the HI as follows:  3b)    H2SO4(l)  +     2HI(g) +    SO2   +      I2      +      2H20  3c)       H2SO4(l)   +      6HI(g) +     S      +      3I2    +      4 H20  3d)       H2SO4(l)   +      8HI(g) +    H2S   +      4I2    +      4 H20  During the reaction one will observe: - ·        Violet Iodine Vapour being evolved, ·        The violet vapour cooling and subliming to form dark solid iodine, ·        A smell of rotten eggs (H2S) ·        Some free yellow sulphur ·        Some HI(g) which could be identified in the way one shows the presence of HCl. Use concentrated NH3 solution

  9. 2006/P1

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