nacl find le f

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NaClFind LEf

Module 3

Practical: Structured Questions2002-7

Welcome and thanks for visiting.

F Scullion. JustChemy.Com

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2004/P1

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Full explanation provided on the next slide

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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.

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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 HCl2a)    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   +      2H2OTherefore, 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

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Ethanol Hexane Cyclohexane Cyclohexene

Increasing carbon/hydrogen ratio = Increasing smoke and soot

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To make the Bunsen valve in this case, use a stopper with two holes. Place a glass tube through the second hole. Then put a piece of rubber tubing on the end of the glass tubing, cut a vertical slit in the rubber tubing and put a glass plug in there.

This valve acts in one direction,It prevents access of air while release of the gas from the flask is permitted

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is primary, secondary or tertiary

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89More detail provided on the next two slides

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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.

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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 HCl2a)    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   +      2H2OTherefore, one will observe a Reddish Vapour  due to some bromine being present.   3a)    KI(s)          +    H2SO4(l)         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

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Please see the next slide

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That’s it. Thanks for listening.

Do consider using the other three parts in this Series: -

Observation & Deduction Planning Titrations

Good luck with your Practical Examination.

F Scullion, JustChemy.Com