• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

Chemistry ATP Tips

Z

Zomane

Messages
26
Reaction score
20
Points
13
TheStallion-Reborn said:
yup ur rite! the equation is correct but those two oxygen atoms in the center are there because one came from the alcohol after H was gone and the other came from the acid after OH was gone.....
Click to expand...

My friend, the acid loses the H ion only - check the structural formula to understand, the acid loses H and alcohol loses OH.
 
Khurram Khalid Iqbal

Khurram Khalid Iqbal

Messages
39
Reaction score
26
Points
28
Some precautions: => Experiments involving poisonous gases like Nitrogen DIOXIDE, Ammonia and Bromine -> Carry out the exp. in Fume Cupboard or in a well Ventilated Room. => Experiments involving heat -> Use a polystyrene cup for insulation to prevent heat loss! + Always take the same initial readings for better accuracy; => Experiments involving Acids, Liquids or Solids -> Always use the same concentration; Same Volumes; Same Surface Area or Same Masses exceptions are some variables! => Experiment involving Crystallisation -> Allow to cool SLOWLY and Use more water and more salt for better results! SOME COMMON and USEFUL precautions for all experiments (use these when your mind is BLANK) => Repetition of the exp. =>Taking Average > Put your tie in shorts => Use Goggles => Taking measurements carefully and multiple measurements , to achieve accuracy ( by finding the average ) => When drawing the best fit line in a graph , do not include points that seem to be out of the curve ,use a sharp and make the curve as smooth as possible , and remember to plot the independent Variable ( Temprature in a Time- of-reaction ( Y ) / Temprature ( X ) graph ) and NEVER forget to write the labels. Tests 1.For Water: > By adding anhydrous Copper(II) Sulphate , which will turn from white to blue. > By adding anhydrous Cobalt(II) chloride , which will turn from blue to pink. 2.For unsaturated hydrocarbon ( Alkenes ) >Liquid : By adding Bromine water to it and shaking. (it'l go from Brown to colourless) >Gas : By passing the compound through Bromine water. (Colour change = Brown to colourless) 3.For purity of substance Solids => Test for melting point , if it is the correct value ( like the data says ) it is pure , if not, it is impure. e.g. Ice at 0 C° Liquids => Test for boiling point , if it is the correct value ( like the data says ) it is pure , if not, it is impure. e.g. Water at 100 C° COLLECTION TECHNIQUES: => upward delivery is for -> gases less dense than air (Hydrogen and Ammonia) => Downward delivery is for -> gases more dense than air (Carbon Dioxide => Displacement of water method -> insoluble gases ( Methane ) Fermentation: => Glucose and Yeast are used! (just rememeber that Yeat contains enzymes -> Biological Catalysts) => Suitable Temperature 37 degrees (Optimum for Enzyme) => Bung is used -> To Let Carbon Dioxide out, and prevent the entry of Oxygen. => Why is Oxygen's entry prevented (-> because it'l oxidize the alcohol to Carboxylic Acid and also it'l affect the anaerobic respiration) => Why does the reaction stop? -> Due to an excess in the conc. of alcohol, Yeast dies. Or Glucose finishes up! Chromatography: => Draw a baseline with a pencil (pencil being insoluble) about 1-2 cm above the end of the chromatogram => Use a pipette to put a concentrated spot of dye on the paper => Dip it in a solvent (Water, if it's soluble in it otherwise an organic solvent e.g Ethanol) => the solvent level MUST be below the baseline => The solvent would start to rise up the paper producing a no. of spots (depending on the no. of dyes present in the substance) => Spray a locating agent for colourless dyes like amino acids or simple sugars => Or identify with RF value (formula = (distance moved by the dye)/ (distance moved by the solvent) Oxidising Agents! => KMn04 (V11) -> FROM PURPLE TO COLOURLESS! => K2Cr2O7 (VI) -> From Orange to Green! All metals are reducing agents! (Mention the Group I metals) Dehydrating Agents : Sulfuring Acid Drying agent : Calcium Oxide
 
Suchal Riaz

Suchal Riaz

Messages
1,983
Reaction score
3,044
Points
273
Zomane said:
My friend, the acid loses the H ion only - check the structural formula to understand, the acid loses H and alcohol loses OH.
Click to expand...

when ester is formed the carboxolic acid does NOT act as acid, alcohol losses H and caboxolic acid loses OH. not H+ or OH-.
there was a debate among many teachers here about this and they finally decided this to be correct.
 
Suchal Riaz

Suchal Riaz

Messages
1,983
Reaction score
3,044
Points
273
all information about potassium managanate, it's formula, equation with reaction with acid and any other thing i need to know.
 
A

Ahmed Raja

Messages
167
Reaction score
38
Points
38
Saad Mughal said:
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, 3 metals are white/silvery white. 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.
Click to expand...
Copied from BMI's page on fb? :D
 
A

Ahmed Raja

Messages
167
Reaction score
38
Points
38
robinhoodmustafa said:
: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
Click to expand...
If moles and conc. is given in standard form then you may write answer in standard form but if it is in decimal use decimal values
 
You must log in or register to reply here.
Top