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Physics, Chemistry and Biology: Post your doubts here!

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Sanchit444

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Can somebody please help me with this question
Chemistry Igcse 0620 May June 2009 variant 31 question 5 b
It is about finding the formula of phosphate of metal T
 
diamondsky

diamondsky

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Sanchit444 said:
Can somebody please help me with this question
Chemistry Igcse 0620 May June 2009 variant 31 question 5 b
It is about finding the formula of phosphate of metal T
Click to expand...
the answer is T3(PO4)2
reason: 8 cm3 reacts fully bcoz ppt height does not increase anymore
so ratio is 12:8 = 3:2
also conc. is same so moles are proportional to volume
 
smart_boy

smart_boy

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diamondsky said:
i dont now if it is by an enzyme bt d answer must be photosynthesis
here light acts as a catalyst for d light reaction wich is breaking down of water molecules
chlorophyll may be an enzyme
for all i noe respiration is not d answer
Click to expand...
Respiration is DEFINITELY controlled by enzymes... This is evident as seeds cannot germinate when boiled because enzymes are denatured so seeds cannot respire and release energy for growth.
Photosynthesis is also controlled by enzymes because if you place the plant at a high temperature, rate of photosynthesis falls because enzymes are denatured, again.
And Chlorophyll is NOT an enzyme... It a chemical needed for photosynthesis..
 
smart_boy

smart_boy

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Vaidik Shah said:
hey why in electrolysis of HCl, hydrogen bubbles seem to form almost instantaneously but chlorine gas seems to form after sum time?
Also could u tell me all gases in which the above is noticed
Click to expand...
I hav come across the question u asked, in one of the past papers.. The answer is that chlorine gas first dissolves in water around the anode and then finally bubbles out... I'm not sure about other gases but usually gases like oxygen and hydrogen are not very soluble in water..
 
smart_boy

smart_boy

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Sam Ivashkov said:
Hi guys. I've got a couple of questions in Physics (Electricity).
Q - When a road tanker pumps oil or petrol into a storage tank, the connecting pipe must be earthed. If it is not, it could become charged. A build up of charge would cause a spark which could make the fuel vapour explode.
i - Why is the rubber hose of a petrol pump made of conducting rubber?
ii -Why must the storage tank and road tanker also be earthed before the fuel is pumped into the storage tank?

Thanks.
Click to expand...
When oil or petrol is pumped, the high speeds they are pumped at, causes friction with the pipes and the container.. If the rubber of the pipe and the material of the tanker are electrical insulators then they can develop a charge because of the rubbing... If a spark gets produced because of collection of charges, the whole oil or petrol can ignite and cause an explosion... To prevent the danger, the tankers and the pipe should be made of conducting materials so that no charge can accumulate... Earthing is necessary so that any charges can be safely conducted to the earth... I guess that's it... :)
 
MaRyy xD

MaRyy xD

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Any tips for Bio Paper 6 ? :S
I real suck at it and I didnt listen to the teacher when she was explaining us about it
What should I do? :'(
 
semsemhosam

semsemhosam

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MaRyy xD said:
Any tips for Bio Paper 6 ? :S
I real suck at it and I didnt listen to the teacher when she was explaining us about it
What should I do? :'(
Click to expand...
i didn't write this, i found it on yahoo answers and found that it summerized everything ... so i pasted it here :) hope it helps :

-Drawing: you will be asked to draw diagrams of fruits, insects..etc. in the exam. Make sure it's in pencil, drawn to the correct size, has definite outlines (no 'sketchy' lines), no shading, no arrow heads when labelling and make sure lines point exactly at the labelled part.

-Comparisons: Make sure the points you use to compare diagrams are visible in the diagrams. Use labels on the diagrams as your guide. And don't compare sizes unless you're given a scale. You can compare numbers shape and proportional sizes.

-Designing an experiment:
*Find the variable which is to be changed (from the question) and mention how you are going to change it (ex: to change temperature, use thermometer-controlled water bath at temperatures 10 to 50 degree Celsius).
*List all variables that you have to keep constant throughout the experiment (ex: room temperature, volume of water, insect species). Make sure there's only one variable for the investigation.
*Mention how long your experiment will last.
*Say how you will measure experiments' results (ex: if you're examining presence of starch, say that the food sample which turns the iodine solution a deeper blue contains more starch)
*Finally: say 'repeat experiment to get more reliable results and minimise error. It's guaranteed to gain you marks.
*If you can, set a control for your experiment. (ex: use boiled enzyme in an experiment to test for enzyme activity)

-Drawing a graph: take care of labels of axes, units, scale, using 'cuts' if needed. Always join points using a ruler unless asked to do otherwise (ex: line of best fit)

-Remember the rule: magnification: drawing/real

-Make sure you know how to test for the presence of water, oxygen, carbon dioxide, starch, reducing sugar, proteins, fats, acid and alkali.

-Look at the experiments in the past papers and make sure you understand them well, as this will help you a lot.

Finally, try answering a couple of exams from the past papers. They're sure to give you a good idea of what to expect , and will certainly boost your confidence

:) :)
 
semsemhosam

semsemhosam

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smart_boy said:
Hi, can you pls help me out with IGCSE Biology nov 2003 paper 3 Q3(b),(c) and (d)...
Pls help as soon as possible cos my exams are not very far... :(
Click to expand...



b) i) because the sewage fungus take in the oxygen for respiration :)
ii)because the fungus starts to decrease & because the aglae are water plants so they give out CO2 during photosynthesis :)
c)i)because sewage contains toxic materials and the suspended materials can float on water so they block the light from the algae so they can'y photosynthesis so their level drops :)
ii)maybe because of overcrowding , less nitrates and maybe because there are fish that feeds on the algae as there is enough oxygen and less suspended solid (toxins)
d) it will kill the algae and the fish ( aquatic organisms )
hope that helps :)
 
Z

zain1245780

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hello guys, im totally new to this forum and had a few question about ELECTROLYSIS (CHEMISTRY).

1: i want to ask that why do Anions ( SO 2- , NO-) which are negatively charged loose their electrons to the anode instead of gaining electrons from it. i mean, if you study the bonding chapter, you come to know that the negatively charged particles gain electron to become stable.

2: secondly, can you plz explain me how to write/make the equation of the reactions at Anode and Cathode (with example). i dont understand where the "arrow" symbol has to be and stuff like that..

your help would be greatly appreciated, THANKS!
 
diamondsky

diamondsky

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zain1245780 said:
hello guys, im totally new to this forum and had a few question about ELECTROLYSIS (CHEMISTRY).

1: i want to ask that why do Anions ( SO 2- , NO-) which are negatively charged loose their electrons to the anode instead of gaining electrons from it. i mean, if you study the bonding chapter, you come to know that the negatively charged particles gain electron to become stable.

2: secondly, can you plz explain me how to write/make the equation of the reactions at Anode and Cathode (with example). i dont understand where the "arrow" symbol has to be and stuff like that..

your help would be greatly appreciated, THANKS!
Click to expand...
1. negetive charges never gain electrons
dey gain em as atom to become negetively charged
2. Summary of electrolysis:
  1. All ionic compounds when molten can be decomposed when electricity is passed through using electrolysis.
  2. The metal and hydrogen always forms at the cathode.
  3. Non-metal always forms at the anode.
  4. Cations travel to the cathode.
  5. Anions travel to the anode.
  6. The electrodes are made from inert material such as graphite, so that they do not involve themselves with the reaction.
  7. The molten substance been electrolysed is called the electrolyte.
Examples:
image004.gif

At the cathode:
image006.gif

At the anode:
image008.gif
image010.gif

At the cathode:
image012.gif

At the anode:
image013.gif
 
Z

zain1245780

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diamondsky said:
1. negetive charges never gain electrons
dey gain em as atom to become negetively charged
2. Summary of electrolysis:
  1. All ionic compounds when molten can be decomposed when electricity is passed through using electrolysis.
  2. The metal and hydrogen always forms at the cathode.
  3. Non-metal always forms at the anode.
  4. Cations travel to the cathode.
  5. Anions travel to the anode.
  6. The electrodes are made from inert material such as graphite, so that they do not involve themselves with the reaction.
  7. The molten substance been electrolysed is called the electrolyte.
Examples:

image004.gif

At the cathode:
image006.gif

At the anode:
image008.gif
image010.gif

At the cathode:
image012.gif

At the anode:
image013.gif
Click to expand...
sorry i cant see anything under these purple headings.... can you retype?
 
diamondsky

diamondsky

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zain1245780 said:
thanks for your effort but still i dont get that why did 'Br' ion lose an electron to anode. instead it should gain one to become a stable atom.
and can you also plz tell me which chapters should i prepare for my ATP IGCSE CHEM EXAM in this oct-nov?
Click to expand...
c
wen Br is in atom state it gains electrons: Br => Br-
but during electrolysis Br is already an ion. so it is Br- => Br coz it already gained an electron earlier to form ion
 
diamondsky

diamondsky

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zain1245780 said:
thanks for your effort but still i dont get that why did 'Br' ion lose an electron to anode. instead it should gain one to become a stable atom.
and can you also plz tell me which chapters should i prepare for my ATP IGCSE CHEM EXAM in this oct-nov?
Click to expand...
u shud concentrate more on electrolysis, chemical tests for ions,rates of reaction, practice sum graphs, learn bout basic lab equipment
organic chem does not usually cum n evn metals n all dat
my suggestion do evrythin
 
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zain1245780

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"Now Br- is an ion and has an extra electron"
" it gains an electron to become a Br atom again"
I GUESS THESE STATEMENTS CONFLICT.
 
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