Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta

Chemistry Unit 3- Recrystalliastion to purify solids watch

Announcements
    • Thread Starter
    Offline

    13
    Hey, could someone please explain to me how this process is done? i.e. whats its purpose etc. please
    Offline

    0
    ReputationRep:
    What exam board are u doing?
    Offline

    1
    ReputationRep:
    Okay, to purify by recrystallisation.. for my exam board, I have to know that:
    The crystals are dissolved in a minimum amount of hot solvent (add it until it just dissolves). Allow the solution to cool, so that the solid crystalises, and then do vacuum filtration, rinsing it with solvent. Dry the crystals.

    It basically works because the solubility decreases with temperature, and during the crystalisation process, the impurities are not added to the lattice.

    Hope this helps,
    Ida

    PS Why do you support Denmark?
    • Thread Starter
    Offline

    13
    (Original post by salmiak)
    Okay, to purify by recrystallisation.. for my exam board, I have to know that:
    The crystals are dissolved in a minimum amount of hot solvent (add it until it just dissolves). Allow the solution to cool, so that the solid crystalises, and then do vacuum filtration, rinsing it with solvent. Dry the crystals.

    It basically works because the solubility decreases with temperature, and during the crystalisation process, the impurities are not added to the lattice.

    Hope this helps,
    Ida

    PS Why do you support Denmark?
    I am doing EDEXCEL. How does vacuum filtration work? I support Denmark because I am from there . Thanks for your help!
    Offline

    2
    ReputationRep:
    recrystallisation isnt on the edexcel unit 3 syllabus though surely?
    Maybe im wrong. tell me if i am but i cant see it anywhere! i know its in 5.5 though..
    • Thread Starter
    Offline

    13
    (Original post by misty)
    recrystallisation isnt on the edexcel unit 3 syllabus though surely?
    Maybe im wrong. tell me if i am but i cant see it anywhere! i know its in 5.5 though..
    It isnt mentioned in the specification ( i dont think), but that has turned up in a previous exam. (Unit Test C3B, 10 June 2002, question 1)
    Offline

    0
    ReputationRep:
    (Original post by Mathemagician)
    It isnt mentioned in the specification ( i dont think), but that has turned up in a previous exam. (Unit Test C3B, 10 June 2002, question 1)
    Maybe it was in the 2002 specification. Is it possible that the 2004 specification could have changed form that? I definitely havent been taught about re-crystallisation/vacuum filtration.
    Offline

    7
    ReputationRep:
    Here is the new specification for unit 3B edexcel AS chemistry. Some things have been taken out such as recrystallisation and some added.

    Topic 3.1B: laboratory chemistry
    Summary of content

    Students will be expected to:
    a) recognise the results of reactions of compounds specifically mentioned in Units 1 and 2 of the specification and the results of tests for simple ions: carbonate, hydrogencarbonate, sulphate (VI), sulphite, chloride, bromide, iodide, nitrate, ammonium, lithium, sodium, potassium, magnesium, calcium, strontium and barium
    b) recognise the chemical tests for simple gases, to include hydrogen, oxygen, carbon dioxide,
    ammonia, chlorine, nitrogen dioxide and sulphur dioxide
    c) describe the techniques used in volumetric analysis and enthalpy change measurements
    d) describe the techniques used in simple organic preparations such as distillation and heating under reflux
    e) recall and interpret details of the chemistry of the elements and compounds listed in Units 1 and 2 of this specification
    • this includes the chemistry of Groups 1, 2 and 7 and the chemistry associated with the organic compounds listed in topic 2.2
    f) interpret quantitative and qualitative results
    g) devise and plan simple experiments based on the chemistry and techniques summarised in a to e above
    h) evaluate error in quantitative experiments
    • see Appendix I for material available to assist centres in teaching this area
    i) comment critically on information concerning experimental procedures
    j) comment on safety aspects of experiments based on supplied data or recall of the chemistry of the compounds listed in Units l and 2. Safety considerations should relate to specific experiments not be of a general nature
    • it will be assumed that students wear eye protection during all practical work.
    • Thread Starter
    Offline

    13
    (Original post by meawinner)
    Here is the new specification for unit 3B edexcel AS chemistry. Some things have been taken out such as recrystallisation and some added.

    Topic 3.1B: laboratory chemistry
    Summary of content

    Students will be expected to:
    a) recognise the results of reactions of compounds specifically mentioned in Units 1 and 2 of the specification and the results of tests for simple ions: carbonate, hydrogencarbonate, sulphate (VI), sulphite, chloride, bromide, iodide, nitrate, ammonium, lithium, sodium, potassium, magnesium, calcium, strontium and barium
    b) recognise the chemical tests for simple gases, to include hydrogen, oxygen, carbon dioxide,
    ammonia, chlorine, nitrogen dioxide and sulphur dioxide
    c) describe the techniques used in volumetric analysis and enthalpy change measurements
    d) describe the techniques used in simple organic preparations such as distillation and heating under reflux
    e) recall and interpret details of the chemistry of the elements and compounds listed in Units 1 and 2 of this specification
    • this includes the chemistry of Groups 1, 2 and 7 and the chemistry associated with the organic compounds listed in topic 2.2
    f) interpret quantitative and qualitative results
    g) devise and plan simple experiments based on the chemistry and techniques summarised in a to e above
    h) evaluate error in quantitative experiments
    • see Appendix I for material available to assist centres in teaching this area
    i) comment critically on information concerning experimental procedures
    j) comment on safety aspects of experiments based on supplied data or recall of the chemistry of the compounds listed in Units l and 2. Safety considerations should relate to specific experiments not be of a general nature
    • it will be assumed that students wear eye protection during all practical work.
    yeah, but the specs changed in 2000.
    Offline

    7
    ReputationRep:
    This is the new spec from 2003
 
 
 
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.