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Chemistry ATP Tips

Discussion in 'Cambridge O Levels' started by Saad Mughal, May 7, 2013.

  1. Saad Mughal

    Saad Mughal

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    Hi everyone! :)
    Hope everyone's having a good time studying. :p
    I've put up this thread to present tips from what I've learnt by doing past papers.

    Firstly, Offer salah and pray to ALLAH (Swt). The most important thing.
    Secondly, Believe in yourself and be confident.
    Now for the actual tips.
    - Read each question carefully and underline/highlight important words/information.
    - When describing colour changes, read the question again, especially in the case of indicators, see that to what is the indicator being added to and what is bringing the colour change.
    - When describing observations, especially reactions with water/solutions, use the words; dissolves, vigorously reacts, colour changes/fades, precipitate forms, the beaker heats up. Do not just give a theoretical answer.
    - Four tables: Solubility of Salts, Tests for Anions, Tests for Cations and Test for Gases should be at your fingertips.
    - Giving answers to reading questions, if there is a measuring cylinder, make sure you read off the flat side of the meniscus.
    - Some common reagents that you should know:
    • Acidified Potassium Manganate (VII) - Oxidizing agent, colour change Purple to Colourless.
    • Acidified Potassium Dichromate (VI) - Oxidizing agent, colour change Orange to Green.
    • Aqueous Potassium Iodide - Reducing agent, colour change from colourless to Brown.
    • Sulphur Dioxide - Reducing agent, no colour change.
    • Concentrated Sulphuric Acid - Drying agent for all gases except Ammonia.
    • Anhydrous Calcium Chloride - Drying agent for all gases except Ammonia.
    • Calcium Oxide - Drying agent for Ammonia and Neutral gases.
    • Ninhydrin - Locating agent for chromatography.
    - When describing manufacturing errors, look carefully at the apparatus to find something odd (such as burettes without taps!).
    - Be able to describe apparatus, such as:
    • Condenser - used for liquifying vapour in distillation and returning unreacted vapour back to the solution.
    • Glass beads - used for cooling the gases in fractional distillation by absorbing heat from them.
    • Fractionating column - to separate the various liquids using their boiling point.
    • Safety bulb - found in pipettes to prevent liquid from entering mouth (when sucking).
    -Do not round off values in titration (or mole) questions! If the value 0.00248 is coming, don't write 0.0025, it will bring about a greater error in the later parts.
    -The following colours of compounds are good to be known.
    1. Group 1, 2 metals are white/silvery white. Group 3 metals are shiny grey. Their compounds are white and their solutions are colourless.
    2. Zinc is a grey solid, its compounds are white.
    3. Lead is a shiny bluish metal, Iron is a shiny blackish solid.
    4. Iron (II) salts are green. Iron (III) salts are red-brown.
    5. Chlorine is a green gas. Silver chloride and Lead chloride are white.
    6. Bromine is a red-brown gas. Silver bromide and Lead bromide are cream coloured.
    7. Iodide is a black solid. Its vapours are purple. Silver iodide and lead iodide are yellow.
    8. Copper is a pinkish solid. Copper (II) sulphate, Copper (II) hydroxide and Copper (II) nitrate are blue.
    9. Copper (II) chloride and Copper (II) carbonate are green.
    10. Nitrogen dioxide is a brown gas. Sulphur and Phosphorous are Yellow solids with different flames.
    - Remember important points of electrolysis, ESPECIALLY selective discharge in concentrated/dilute solutions. Remember that displacement and electrolysis are redox reactions.
    - Remember important equations such as:
    1. Group 1 Elements (Metals) + H2O ---> Metal OH + Hydrogen Gas
    2. Acid + Metal ---> Salt + Hydrogen Gas (Copper, Silver,Gold DO NOT REACT)
    3. Acid + Bases ---> Salt + Water
    4. Acid + Carbonate ---> Salt + Water + Carbon Dioxide
    5. Alkalis (Metal Hydroxide) + Ammonia Salts ---> Ammonia gas + Water + Salt
    6. Acidic Oxide + Water ---> Acid
    7. Neutral Oxide + Air ---> Acid
    8. Basic Oxide + Acid ---> Salt + Water
    9. Alkene + Steam ---> Alcohol
    10. Glucose + Yeast ---> Ethanol + CO2
    11. Acid + Alcohol ---> Ester + Water
    12. Alcohol (when oxidized) ---> Organic Acids + Water
    - In identifying ions, remember, if transition metal is present, a coloured SOLUTION will be formed not a coloured COMPOUND.
    - Also, when giving the test for Nitrate ions, don't forget the heat, it carries one mark.
    - Use a sharp pencil and plot a clean, clear graph.
    - For describing presence of gases (after reaction), use words, effervescence and bubbling.
    - The heating is done in the fume cupboard to ensure that students are not exposed to the poisonous gas, nitrogen dioxide. The toxicity of the gas is the point to mention. (from markscheme).
    - Remember, only potassium, sodium, calcium react with water to form hydroxides, all the metals below (till copper) react with STEAM to form metal oxides.
    - Also, remember that sodium and potassium compounds are very stable that do not break down on heating (their hydroxides break down to oxides and hydrogen on heating though).
    - Finally, best of luck to everyone giving Chemistry tomorrow! The best tip is to solve past papers, there is still ample time left!


    I request anyone seeing this thread to add anything they would like to advice others! Hope this helps you people! :)
    Please pray that we all get A*'s. :)
    P.S. I'll add more things when I remember something.
     
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  3. robinhoodmustafa

    robinhoodmustafa

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    Thanks. Very Helpful
     
  4. passion hunter

    passion hunter

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    u my friend are a f****** legend!!!!
     
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  5. Saad Mughal

    Saad Mughal

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  6. Saad Mughal

    Saad Mughal

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    We can use the word liquify. I was describing the use. I'll correct it. Thanks. :)
     
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  7. AhsanAfzal

    AhsanAfzal

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    no problem. good job btw
     
  8. Saad Mughal

    Saad Mughal

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    Thanks. :)
     
  9. ijlalm

    ijlalm

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    do we have to join the curve with a scale or a freehand drawing is required??
     
  10. Saad Mughal

    Saad Mughal

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    Curve should be drawn with a freehand.
     
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  11. AhsanAfzal

    AhsanAfzal

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    Acidic Oxide + Air ---> Acid
    pls explain this Saad Mughal
     
  12. robinhoodmustafa

    robinhoodmustafa

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    Saad Mughal

    Can we write down Moles Values in Standard Form? Like 2.57 x 10^-3
     
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  13. robinhoodmustafa

    robinhoodmustafa

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    It shoud be Acidic Oxide + Water.
     
  14. Ammarfasih

    Ammarfasih

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    Thanks Mughal U r awesom .... :D
     
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  15. Saad Mughal

    Saad Mughal

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    I don't know for sure because the mark scheme does not say anything about this. It's better that you write it in decimal form because we don't know for sure!
     
  16. AhsanAfzal

    AhsanAfzal

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  17. Saad Mughal

    Saad Mughal

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    Actually, this is incorrect, sorry, it is Neutral Oxide + Air ---> Acidic Oxide.
    AhsanAfzal.
    Sorry for the mistakes, I wrote this in a hurry. :/
     
  18. robinhoodmustafa

    robinhoodmustafa

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    :p Pls ask someone. Its Important
    I wrote Standard form values in my Mocks paper and they were accepted but School Teachers and CIE examiner.. Big Diff
     
  19. Zomane

    Zomane

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    1. Carbon dioxide is an acidic gas which turns moist blue litmus red.
    2.Same goes for chlorine - chlorine also bleaches the litmus white.
    3.Ammonia is a basic gas and turns red litmus blue.
    4. Sulphur dioxide is acidic too.

    Some indicators for acids and alkalis are below:
    Indicator - Color in Acid - Color in Alkali
    1.Litmus - red - blue
    2.Methyl orange - red - yellow/pink
    3. Phenolphthalein - colorless - light pink
    4. Screened methyl orange - red - green
    5.Bromothyl blue - yellow - blue

    Also:
    Silver chloride, lead(II) chloride, calcium sulphate, barium sulphate, lead(II) sulphate, are insoluble.
    Also all carbonates and sulphides are insoluble except Potassium, sodium and ammonium sulphides/carbonates.

    Also this formula will help alot:
    Concentration = mole OR mass/volume
    REMEMBER to convert volume to dm3 or cm3 as per requirement.

    Also when an ester is formed, the formula will be like this:
    C2H5OH + C2C5COOH ---> H2O + C2H5COOC2H5, also written as C2H5COOHCH2CH3
    Which means that the hydrogen of the carboxylic acid will react with the last OH of alcohol, and in pleace of the hydrogen put the alcohol without the OH.

    Aluminum oxide is a drying agent.

    Unless the curve is ACTUALLY smooth you will not get a correct value.

    In electrolysis if you want to INCREASE the amount of the pure substance on the cathode, use an anode of the same metal. For example if you want more silver to be formed on cathode during electrolysis, use a silver nitrate solution and silver anode.

    -Zomane
     
  20. robinhoodmustafa

    robinhoodmustafa

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    See So2 is a Acidic oxide.. And when add in water.. Forms H2s04

    Just like this.. Co2 + water gives carbonic acid
     
  21. Saad Mughal

    Saad Mughal

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    Yeah, I know. I corrected it.
    It is neutral oxide + air ---> acidic oxide.
     

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