Join TSR now and get all your revision questions answeredSign up now
    • Community Assistant
    • Welcome Squad
    Offline

    3
    ReputationRep:
    (Original post by morganlethbridge)
    ah right what is precipitating
    A precipitation occurs when the solution can no longer support the solid in solution. As temperature falls, solubility decreases. If solubility decreases, the solid can no longer be dissolved so drops out of solution as a precipitate.
    So a precipitate is an insoluble solid formed by a reaction taking place in solution.
    Offline

    1
    ReputationRep:
    (Original post by morganlethbridge)
    ah right what is precipitating
    An insoluble solid formed by a reaction taking place in a solution
    (so how like limewater turns milky an produces an insoluble precipitate of Caco3)
    • Community Assistant
    • Welcome Squad
    Offline

    3
    ReputationRep:
    Here is a summary of what others have posted regarding acids, alkalis and bases and the methods to produce salts

    Acid: A substance with a PH less than 7. Forms H+ ions in water. Base: A substance with a PH over 7.
    Soluble bases are alkalis which form OH- ions in water.


    Acid + Base = Salt + Water
    In ionic form: H+(aq) + OH-(aq) = H20(l)
    This is the basic neutralisation reaction. The products of a neutralisation reaction are always neutral, hence the name.


    Other useful neutralisation reactions:


    Acid + Metal = Salt + Hydrogen (unless metal is less reactive than H2)


    Acid + Metal Oxide = Salt + Water
    Acid + Metal Hydroxide = Salt + Water
    Acid + Metal Carbonate = Salt + Water + Carbon Dioxide



    Most metal oxides and hydroxides are bases (insoluble).




    Acid + metal or insoluble base to make a soluble salt
    1. Add the metal/metal oxide/metal hydroxide to the acid2. The reaction will have finished when the excess solid sinks to the bottom of the conical flask.
    3. Filter out the excess metal/metal oxide/metal hydroxide and you will have the salt solution left.
    4. Evaporate some of the water to concentrate the solution using a bunsen burner.

    5. Leave the rest to evaporate slowly. This is known as crystallisation.


    Acid + alkali to make a soluble salt
    1. Add indicator to acid2. Add alkali until indicator changes colour and record how much alkali was used
    3. Repeat this using exactly same volumes of alkali and acid but without the indicator so that the salt isn't contaminated
    4. Then evaporate the water to concetrate the solution
    5. Leave the rest to evaporate slowly (crystallisation)



    Making an insoluble salt (precipitation)
    1. Mix two solutions containing ions you need (i.e. for lead chloride you could mix lead nitrate solution and sodium chloride solution)

    2. Once precipitation has occurred (it will leave a solid), you just filter the solution

    3. Wash and dry precipitate on filter paper
    Offline

    1
    ReputationRep:
    (Original post by Georgie99)
    I'm so worried about this exam, I don't feel ready :/ Do you guys think it'll be an easy paper?
    Since b2 was hard then it's probable that c2 will also be difficult.
    Offline

    2
    ReputationRep:
    Okay can you give examples of
    reactions of each one
    i.e potassium hydrxiide qn on june 2012 was crystalisation
    Offline

    0
    ReputationRep:
    That was the 2014 question. Doubt that it'll come up again!
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by kaypd)
    Since b2 was hard then it's probable that c2 will also be difficult.
    Our teacher said that Chemistry is the converse to the Biology exams in terms of difficulty, so I'd say Chemistry will probably be a little easier this year.
    Offline

    1
    ReputationRep:
    My predictions for B2 are:
    - almost definitely a question on thermosetting/softening polymers, because it hasn't come up in the past four years
    - the 6 marker is unlikely to be a method to do with producing salts, because the B2 six marker was a method (my money is on structure of macromolecules but I'm unsure)
    - hopefully nothing on nano particles because there was a large-ish section on them last year

    praying for a good one!
    Offline

    2
    ReputationRep:
    (Original post by ssssara)
    thank you so so so so much! I really appreciate it thank you. Good luck tomorrow x
    It's okay! I hope you saw my answer to your question on graphite too, and you too!
    Offline

    2
    ReputationRep:
    In case anyone might find it useful, I did a practice answer on electroplating earlier today:

    Explain how and why a copper cup would be electroplated with silver.

    The cup would act as the negative electrode, and the positive electrode should be a block of pure silver metal. The electrolyte used needs to be an ionic substance containing ions of the plating metal (silver). For example, silver nitrate solution could be used. It is important that the electrolyte is in solution so that the ions can move to carry charge. The silver ions in the electrolyte will move to the negative electrode (the cup) because they are positively charged. Here each silver ion will gain 3 electrons and be reduced to silver atoms, hence the cup will be plated with silver metal. The silver metal at the positive electrode is required to top up the solution with silver ions. Electroplating is done to coat the surface of one metal with another. In this case, it is done for decoration, to make the cup look nice, because making a pure silver cup would be too expensive.

    Would anyone add anything else? Thanks
    Offline

    1
    ReputationRep:
    (Original post by neil20143)
    Our teacher said that Chemistry is the converse to the Biology exams in terms of difficulty, so I'd say Chemistry will probably be a little easier this year.
    I do hope so.
    Offline

    1
    ReputationRep:
    what is their to know about polymers??
    Offline

    0
    ReputationRep:
    Anyone know what the most frequently asked questions are on??
    Offline

    0
    ReputationRep:
    (Original post by morganlethbridge)
    what is their to know about polymers??
    The difference between thermosetting and thermosoftening and LD and HD
    Offline

    3
    ReputationRep:
    (Original post by olivialloyd)
    Yes please! That would be so helpful
    Hope this helps!

    Name:  image.jpg
Views: 123
Size:  567.5 KB
    Offline

    1
    ReputationRep:
    Chemistry is my worst science, I usually only get As, occasional A* but I am feeling the pressure for this exam.. I haven't revised in months because I am a bit of a loon, genuinely- not just for not revising. We'll all do fine! Hopefully it's more challenging than the Biology paper! I love chemistry.
    Offline

    2
    ReputationRep:
    (Original post by morrissies)
    My predictions for B2 are:
    - almost definitely a question on thermosetting/softening polymers, because it hasn't come up in the past four years
    - the 6 marker is unlikely to be a method to do with producing salts, because the B2 six marker was a method (my money is on structure of macromolecules but I'm unsure)
    - hopefully nothing on nano particles because there was a large-ish section on them last year

    praying for a good one!
    JEEEZ you confused me with "macromolecules" and its ok people, its just giant covalent structures, ie. sharing of molecules etc.
    Offline

    0
    ReputationRep:
    does anyone think that there'll be a six mark question on electrolysis??
    Offline

    2
    ReputationRep:
    (Original post by ssssara)
    does anyone think that there'll be a six mark question on electrolysis??
    well i hope so because i'm good at that, and there were none last year so yiou never know
    Offline

    1
    ReputationRep:
    (Original post by hrmpurser)
    well i hope so because i'm good at that, and there were none last year so yiou never know
    I hope so too!
 
 
 
Poll
How are you feeling about your A-level results?

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

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