Chemistry Revision

[Zardonz]

sry not the doubts post , the name of the post is "Maths paper 4 discusssion "

 

[zkapoor]

zkapoor...
i would say that the study guide is correct because we don't apply simple distillation to separate ethanol and water even though they have a difference 25 degrees in their boiling points.
and anyway, how will you know in the exam whether the two liquids have a difference of 25 degrees in their boiling points.
its safer to go with fractional distillation to seperate two miscible liquids.



i have another question....recently i noticed that in the past papers they used "diffusion" as a seperation technique. How does that work?
My chemistry teacher never told us how to use diffusion to seperate substances.

Cheers mate, I guess that's true.

For the diffusion thing, I'm not 100% sure how it works but I know they use the different rates of diffusion to help separate things. I think it's probably like they put the gases in a container with another porous container inside and after a long time all that should be left in the porous container will be the heavier gas... I'm really not sure though.
It definitely has to do with the different rates of diffusion though.

 

[zkapoor]

zkapoor...
i would say that the study guide is correct because we don't apply simple distillation to separate ethanol and water even though they have a difference 25 degrees in their boiling points.
and anyway, how will you know in the exam whether the two liquids have a difference of 25 degrees in their boiling points.
its safer to go with fractional distillation to seperate two miscible liquids.



i have another question....recently i noticed that in the past papers they used "diffusion" as a seperation technique. How does that work?
My chemistry teacher never told us how to use diffusion to seperate substances.

Cheers mate, I guess that's true.

For the diffusion thing, I'm not 100% sure how it works but I know they use the different rates of diffusion to help separate things. I think it's probably like they put the gases in a container with another porous container inside and after a long time all that should be left in the porous container will be the heavier gas... I'm really not sure though.
It definitely has to do with the different rates of diffusion though.

Alternately, what they might mean by it is if one gas is denser than the other, they just leave the gases to settle and tap off the denser one from the bottom of the container. It's unlikely though, cause that doesn't really have to do with diffusion

 

[xIshtar]

Basically, the rate of diffusion depends on the mass, which allows for it's use in seperation techniques.

 

[zkapoor]

Basically, the rate of diffusion depends on the mass, which allows for it's use in seperation techniques.

What he said. I'm pretty sure you don't need to know the exact technique to use, so just know that diffusion can be used to separate gases

 

[dancingmaster]

Re: Chemistry Paper 6 Revision

i forgot sulfuric acid dries gases in the exam i wrote it cleans the gas

in the last question i wrote you heat copper carbonate to get copper oxide then you heat copper oxide with carbon to get carbon dioxide and copper. can i get full marks?

and for the graph, one line went straight up then straight down, so i drew it with a ruler... but some of my friends said thats wrong :S

btw i've been reading these forums for the past week but i only joined today, so hi

Well it is not entirely incorrect. I have done past papers where this is allowed but i do CIE IGCSE, so Edexcel may be different. (I know you are not in CIE because our chemistry paper 6 is going to happen on 25th.Wish me luck!)

 

[dancingmaster]

Hey can neone tell me what to revise the day before the exam. I have done everything i could otherwise. Thanks a lot.

 

[ssms396]

zkapoor...
i would say that the study guide is correct because we don't apply simple distillation to separate ethanol and water even though they have a difference 25 degrees in their boiling points.
and anyway, how will you know in the exam whether the two liquids have a difference of 25 degrees in their boiling points.
its safer to go with fractional distillation to seperate two miscible liquids.



i have another question....recently i noticed that in the past papers they used "diffusion" as a seperation technique. How does that work?
My chemistry teacher never told us how to use diffusion to seperate substances.

Cheers mate, I guess that's true.

For the diffusion thing, I'm not 100% sure how it works but I know they use the different rates of diffusion to help separate things. I think it's probably like they put the gases in a container with another porous container inside and after a long time all that should be left in the porous container will be the heavier gas... I'm really not sure though.
It definitely has to do with the different rates of diffusion though.

Alternately, what they might mean by it is if one gas is denser than the other, they just leave the gases to settle and tap off the denser one from the bottom of the container. It's unlikely though, cause that doesn't really have to do with diffusion

Basically, the rate of diffusion depends on the mass, which allows for it's use in seperation techniques.

What he said. I'm pretty sure you don't need to know the exact technique to use, so just know that diffusion can be used to separate gases

Thank you all for the explanation...it helps.
but i just hope they make the paper easy. Don't want to take any risks.

 

[zkapoor]

No problem =)
Actually, it's better if the exam is hard =P
Harder exam = lower grade boundaries. And when I say hard I just mean higher-level thinking is required. I'm pretty sure you're capable of that so should be fine... So better chance of getting an A* with a harder paper. I know, strange logic =P

 

[KurayamiKimmi]

DOUBTS!!! :unknown:
DOUBT 1
http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf

question number 6d could some1 explain the answer ? pwease? =D

Doubt 2
http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf

question number 6c ..wth is that ?

 

[xIshtar]

DOUBTS!!! :unknown:
DOUBT 1
http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf

question number 6d could some1 explain the answer ? pwease? =D

Doubt 2
http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf

question number 6c ..wth is that ?

No 6d?

Okay, for 6c, if I get the question that you are talking about right. You basically have to refer to the graph, and say what cooling from 60-20 does, ie, mention the crystαls, state figures too as they get you marks.

 

[zkapoor]

DOUBTS!!! :unknown:
DOUBT 1
http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf

question number 6d could some1 explain the answer ? pwease? =D

Doubt 2
http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf

question number 6c ..wth is that ?

No 6d?

Okay, for 6c, if I get the question that you are talking about right. You basically have to refer to the graph, and say what cooling from 60-20 does, ie, mention the decrease or increase in solubility, state figures too as they get you marks.

It probably wouldn't hurt to mention crystallisation of the salt either

 

[skinnyboyfat]

I am having trouble with appratus names ....they are not in my book...can some1 plz help me....paper tomorrow....pm me or notify me by any means..plz

 

[JmCullen]

hey! can i know what to study for my practical paper 5 chemistry????
test of ions???? test of gases??? what else?

 

[irlzs95]

in nov 2010 q3 part b nd c , why not the opposite ?
like i said in b acid is used up nd in c to prevent co2 from escaping !

how come CO2 will be given off ?? there is a stopper !

http://www.xtremepapers.me/CIE/Cambridg ... _qp_62.pdf

 

[alexxx04]

hey! can i know what to study for my practical paper 5 chemistry????
test of ions???? test of gases??? what else?

From the CIE IGCSE Chemistry syllabus for Paper 5:

Candidates may be asked to carry out exercises involving:
• simple quantitative experiments involving the measurement of volumes
• speeds of reaction
• measurement of temperature based on a thermometer with 1 °C graduations
• problems of an investigatory nature, possibly including suitable organic compounds
• simple paper chromatography
• filtration
• identification of ions and gases as specified in the Core curriculum (the question papers will include
notes on qualitative analysis for the use of candidates in the examination.)

Candidates may be required to do the following:
• record readings from apparatus;
• describe, explain or comment on experimental arrangements and techniques;
• complete tables of data;
• draw conclusions from observations and/or from information given;
• interpret and evaluate observations and experimental data;
• plot graphs and/or interpret graphical information;
• identify sources of error and suggest possible improvements in procedures;
• plan an investigation, including suggesting suitable techniques and apparatus.
Candidates will not be required to carry out weighing for the practical test.

Good luck ;-)

 

[JmCullen]

hey! can i know what to study for my practical paper 5 chemistry????
test of ions???? test of gases??? what else?

From the CIE IGCSE Chemistry syllabus for Paper 5:

Candidates may be asked to carry out exercises involving:
• simple quantitative experiments involving the measurement of volumes
• speeds of reaction
• measurement of temperature based on a thermometer with 1 °C graduations
• problems of an investigatory nature, possibly including suitable organic compounds
• simple paper chromatography
• filtration
• identification of ions and gases as specified in the Core curriculum (the question papers will include
notes on qualitative analysis for the use of candidates in the examination.)

Candidates may be required to do the following:
• record readings from apparatus;
• describe, explain or comment on experimental arrangements and techniques;
• complete tables of data;
• draw conclusions from observations and/or from information given;
• interpret and evaluate observations and experimental data;
• plot graphs and/or interpret graphical information;
• identify sources of error and suggest possible improvements in procedures;
• plan an investigation, including suggesting suitable techniques and apparatus.
Candidates will not be required to carry out weighing for the practical test.

Good luck ;-)

thanks! i'll have my exam tomorrow.. urgh~ :%)

 

[WayneRooney10]

Okay guys. I have Chemistry Paper 6 tomorrow. What topics should I revise? And what should I know?

 

[JmCullen]

Okay guys. I have Chemistry Paper 6 tomorrow. What topics should I revise? And what should I know?

hey there!
I'm not having paper 6 tomorrow, i'm having paper 5 instead..
but, i've done some paper 6 for my revision..
as what i've observed from paper 6, they usually have question like test for ions.
for example, mixture X is added to sodium hydroxide, what colour will the solution turns to?
So, probably you have to memorise the colour of the ppt and when add excess, what will happen..

hope this help.

 

[medevil]

Some notes about Moles

let me give some general details:

-Define mole:1 mole of any substance is its Ar or Mr expressed in grams

-no. of moles = mass of substance/mass of one mole

-no. of moles of gas = volume in dm3 /24 (1dm3=1000cm3)

-no. of moles of solute= conc. X volume (be careful in units either all dm3 or cm3)

-(u shud know how to rearrange an eqn.)

-when the reaction involve only gases then we can use the ratio of volumes instead of mole ratio.

-Percentage yield = actual yield/theoritical yield X100

-Percentage purity = mass of pure substance / mass of impure substance X 100

-steps for finding molecular formula

---find no. of moles(method of finding this differs according to question)

---hence find the mole ratio

---and then calculate emperical formula

---find n which is=>relative molecular mass/emperical formula mass

---then find molecular formula=>(emperical formula)n and simplify

-finally what SuperXDE said practice some past paper question as Practice makes a man perfect!!

Mole ( Curses ) and their rules :

• One Mole is 6.02 × 10^23 Molecules of an Element ( or Atoms , in case of a pure non-reacted element ) , a mole of En is equal to n×E'sMass in grams and it contains 6.02 × 10^23 ( Twenty one zeroes , this number is called Avogrado's constant )
  where E stands for Element or molecule and n stands for the number of elements or molecules ( ¬¬" ).
  One mole's volume of a gas at room temperature is 24 dm^3 ( 24 Litres )
  Mole = Concentration × Volume
  Mole = Volume of Gas / 24dm^3
  Mole = Mass of Total substance / 1 mole ( 1 mole or Relative Atomic/Molecular mass in Grams )
  Ratio in compound xy3 is x:3y , in other words , mole(x):3mole which is also 1:3

Hope this new update helps with the "amazing" Mole calculation part. I'm Lovin' it ( Obviously a liar ) and sorry for complicating.

Here are a couple of tests that I copied from my book , IGCSE Chemistry , Printed and published by Cambridge University by Richard Harwood


Testing for Anions ( Negative Ions ) :

• Carbonate ( CO3 2- ), add dilute hydrochloric acid ,result is effervescence , carbon dioxide produced ( test with limewater )

• Chloride in solution ( Cl- ) , acidify solution with dilute nitric acid then add aqueous silver nitrate , result is white ppt. of silver chloride formed. ( ppt soluble in ammonia solution )

• Bromide in solution ( Br- ) acidify solution with dilute nitric acid then add aqueous silver nitrate , result is cream ppt. of silver bromide formed , ( only slightly soluble in ammonia solution )

• Iodide in solution ( I- ) acidify with dilute nitric acid then add aqueous silver nitrate , result is yellow ppt of silver iodide , insoluble in ammonia solution OR acidify with dilute nitric acid then add lead nitrate solution , result yellow ppt. of lead iodide formed.

• Sulphate in solution ( SO4 2- ) acidify solution with dilute hydrochloric acid then add barium chloride solution , OR acidify solution with dilute nitric acid then add barium nitrate solution , result for both is white ppt of barium sulphate formed.

• Nitrate in solution ( NO3 - ) make alkaline with sodium hydroxide solution then add aluminium foil ( or Devarda's alloy ) and warm carefully , result is Ammonia gas is given off ( test with moist red litmus ).

Testing for Metal ions by burning :

• Sodium (Na+) burns giving yellow flame.

• Potassium (K+) burns giving lilac flame ( pale violet ).

• Calcium (Ca2+) burns giving brick-red flame.

• Lithium (Li+) burns giving crimson flame.

• Copper (Cu2+) burns giving a blue-green flame.

• Barium (Ba2+) apple-green (chartuese , close to lime a bit I think ).

Testing for Positive ions in solutions by adding sodium hydroxide:

• Ammonium (NH4 +) , ammonia produced on warming.

• Copper(II) (Cu 2+) , light blue gelatinous ppt. of copper hydroxide ( insoluble in excess sodium hydroxide ).

• Iron(II) (Fe 2+) , green gelatinous ppt. of iron(II) hydroxide ( insoluble in excess ).

• Iron(III) (Fe 3+) , rust-brown gelatinous ppt. of iron(III) hydroxide ( insoluble in excess ).

• Calcium (Ca 2+) , white ppt of calcium hydroxide ( insoluble in excess ).

• Magnesium (Mg 2+) white ppt. of magnesium hydroxide ( insoluble in excess ).

• Zinc (Zn 2+) , white ppt. of zinc hydroxide ,soluble in excess ,giving a colourless solution.

• Aluminium (Al3+) white ppt. of aluminium hydroxide , soluble in excess ,giving a colourless solution.

Testing for Positive ions in solutions by adding ammonia solution:

• Ammonium (NH4 +) , ----- ( I think it means no reaction ).

• Copper(II) (Cu 2+) , light blue gelatinous ppt. dissolves in excess ammonia , giving a deep blue solution.

• Iron(II) (Fe 2+) , green gelatinous ppt. of iron(II) hydroxide ( insoluble in excess ).

• Iron(III) (Fe 3+) , rust-brown gelatinous ppt. of iron(III) hydroxide ( insoluble in excess ).

• Calcium (Ca 2+) , no ppt. (or only a very slight ppt.).

• Magnesium (Mg 2+) white ppt. (soluble in excess).

• Zinc (Zn 2+) , white ppt. (soluble in excess).

• Aluminium (Al3+) white ppt. (insoluble in excess.

Testing for gases:

• Ammonia (NH3) , colourless and pungent smell , hold damp red litmus paper ( or universal indicator paper ) in gas , Indicator paper turns blue..

• Carbon dioxide (CO2) , colourless and odourless , bubble gas through lime water ( calcium hydroxide solution ) , white ppt. of calcium carbonate formed ( solution turns milky ).

• Chlorine (Cl2) , pale green and choking smell , hold damp litmus paper ( or universal indicator paper ) in gas , indicator paper is bleached white ( blue litmus will turn red first ).

• Hydrogen (H2) , colourless and odourless , hold a lighted splint in gas , hydrogen burns with a squeaky 'pop'.

• Oxygen (O2) , colourless and odourless , hold a 'glowing' wooden splint in gas . the splint relights.

• Sulphur Dioxide (SO2) , colourless and choking smell , dip a piece of filter paper in pottasium dichromate(vi) solution and hold it in gas . solution turns pale green ( SO2 is a reducing agent ).

Testing for purity of substance :

• Solids : Testing for melting point , if it is the correct value ( like the data says ) therefore it is pure , if not hence it is impure. e.g. Ice at 0 C°

• Liquids : Testing for boiling point , if it is the correct value ( like the data says ) therefore it is pure , if not hence it is impure. e.g. Water at 100 C°

Drying agents :

• Concentrated Sulphuric acid : used to dry all gases except ammonia.

• Anhydrous calcium chloride : used to dry all gases except ammonia which forms a complex with calcium chloride.

• Calcium oxide : used to dry ammonia and neutral gases.

Testing for water and acidity :

• pH Testing (1) :

• • Acidity and Alkalinity are found by Indicators ( Usually Universal Indicator and Litmus paper )

• • For a more accurate result , use pH Meter

• Testing for water :

• • By adding anhydrous Copper(II) Sulphate , which water will turn from white to blue

• • By adding anhydrous Cobalt(II) chloride , which water will turn from blue to pink ( or deep rose )

Organic Analysis : ( Yet still under construction )

• Testing for unsaturated hydrocarbon ( Like Alkenes )

• • Liquid : By adding Bromine water to it and shaking.

• • Gas : By passing the compound through Bromine water.

• If it is an unsaturated hydrocarbon , it will turn the orange-brown Bromine water colourless

• Food tests : ( Testing for nutrients)

• • Detecting starch in food ( and water of course ) : Adding Iodine solution which will give a blue-black colour , indicating the presence of starch

• • Detecting glucose in food ( and water of course ) : Add sugar-test ( Benedict's solution ) food and water , and heat it , it will give an orange-red ppt. , indicating presence of glucose

• • Detecting protein in food ( and water of course ) :

• • • 1. Add dilute sodium hydroxide

• • • 2. Add drops of copper(II) sulphate solution

• • Violet colour indicates the presence of protein

• • Detecting fat in food :

• • • 1. Smear food on paper

• • • 2. Leave to dry

• • • 3. Hold up to the light

• • Bright glossy area indicates the presence of fats

Test for Ethanoic acid and Ethanol : ( as in the book )

• the two substances provide a simple test reaction for each other. They both react with each other with the addition of a few drops of concentrated sulphuric acid , producing a sweet-smelling ester , the mixture is warmed gently and the fruity smell of the ester can be best detected by pouring the reaction mixture into a beaker of water. this spreads the ester and disperses the distinctive 'pear-drop' smell.

Chromatography :

• Individual monomers from proteins and carbohydrates can be separated by chromatography and detected using locating agents because they are colourless. if a Sample gives only one spot , therefore that sample is pure , use more than one solvent for accuracy and making sure that it is pure. For 2D ( 2 Dimensional ) Chromatography , user the paper and get the results on one dimension ( Y ) then you dry the paper from the solvent then you rotate it by 90° to get the other dimension ( X ) , and it will give us the 2D chromatography that we always see in the book

Reducing error in experiments :

• Using more accurate apparatus that has a reduced percentage of Systematic errors ( these cannot be avoided , the systematic errors in any tool in the world , No atomic computers that can do this accurately ¬¬ )

• 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.

What to do next :

• Apparatus names , Apparatus names and Apparatus names , revise them and do not mistake a boiling tube for a test tube ( They are almost clones of each other )

• This post does not , does not contain everything to be able to score an A* in the Exam , so STUDY!

• Visit this page , Pray well , Have fun sleeping , Eat before the exam by 3~4 hours , and do not eat/drink anything before it and remember that no one lives forever . . . you will die anyway , no need to be nervous , crazy . Just be calm and try to be theoretical , and once you finish the exam hurry to home , have a simple nap , STUDY MATHS , HAHAHAH...

More info from other members :

• Solubility of salts , By member Larina (*)

• • all nitrates are soluble
    all potassium, sodium and ammonium salts are soluble
    all sulphates are soluble except barium sulphate, lead sulphate and calcium sulphate
    all chloride and iodide salts are soluble except silver chloride/iodide, lead chloride/iodide and mercury chloride/iodide
    all sulphides are insoluble except K, Na and ammonium salts
    all carbonates are insoluble except K,Na and NH4 salts
    all hydroxides are insoluble except K,Na and NH4 salts and magnesium and calcium hydroxide salts are partially soluble.

LEGEND : What to be tested for , Test , Alternative Test , Result , Colour and Smell States of Matter


(1) : pH measurements and other analyses are often carried out on soil samples. Soil is stirred with distilled water. The insoluble material settles out, but the solution above remains unclear because of fine suspended particles. These fine particles can be made to settle too by adding some barium sulphate to the suspension. The barium sulphate particles , themselves insoluble, physically drag the fine suspended material to the bottom of the container. The mixture can then be filtered and the solution tested in various ways for soluble ions , pH , etc.

(*) Special thanks for Larina ,Hope she forgives me forI quoting that without permission ¬¬" , The quote was edited by SuperXDE in refrence to Yahoo! Answers

if you have any questions do not hesitate asking!

umm i think Mg2+ is soluble in excess ammonia