Physics, Chemistry and Biology: Post your doubts here!

[Penalopi]

In physics macroscopic properties ( as of what i know)
Are properties such as Density, Pressure (of Gases), Volume (of gases/liquids), Length (of solids) and Resistance (of wires) which change with change in temp (they could be measured, to measure temp. ex thermometer uses volume of mercury)

Hope this helped you

Isn't this out of sylabus??

 

[thats_me]

May/June 2011 Chemistry Paper 3

Q)1
Q)2ai
Q)3c
Q)4aiii
Q)5a
Q)5b
Q)5c

Sry if Im being an idiot...plz help me with those questions....thx

i hope this is the one

1a: all gases so diffusion (F)
b: water needed so simple distillation (A)
c: identification of amino acids so chromatography (D)
d: iron filings insoluble so filtration (E)
e: crystals needed so evaporation (C)
f: liquid alkanes have bp so fractional distillation (B)

2ai: photosynthesis , in which chlorophyll traps sunlight and converts it to chemical energy.....

3ci :They are strongly bonded and so Its very hard to break the bonds between them
ii: As its ions are in layers which can slide over eachother

4aiii: As they have diff boiling points , lowest bp will be distilled first i.e cadmium then zinc then lead

5ai: metal + acid ---> salt + hydrogen
= so 2Li + 2HI ---> 2LiI +H2
ii: metal carbonate + acid ---> salt + CO2 +H2O
= s0 Zinc carbonate +Hydiodic acid ---> Zinc iodide + Carbondioxide + water
iii: Metal oxide+ acid ---> salt + water
= so MgO + 2HI ---> MgI2 + H2O
b: the first is redox as electrons are transfered (Li + 2H+ --->li+ +H2)<-- the ionic eqn
c: when chlorine is bubbled disblacement occurs as it is more reative than bromine and iodine
so hydriodic -->grey solid as iodine forms
hydrobromic ---> brown vapours as bromine forms

 

[Ahmedm96]

i want good notes for organic chemistry cant memorize anything

 

[thats_me]

i want good notes for organic chemistry cant memorize anything

check here http://www.xtremepapers.com/communi...y-revision-guide-according-to-syllabus.16647/

 

[GriM ReapeR]

i have a doubt in physics.. (in logic gates chapter) can we invert the inputs in a truth table? like for example, for AND gate,
A B F
0 0 0
0 1 0
1 0 0
1 1 1

can we do this? :
A B F
0 0 0
1 0 0
0 1 0
1 1 1

i had a class test about this and i wrote the inverted one, but the teacher did not accept it? why? is there a certain way we have to do this?

thanks.

 

[thats_me]

i have a doubt in physics.. (in logic gates chapter) can we invert the inputs in a truth table? like for example, for AND gate,
A B F
0 0 0
0 1 0
1 0 0
1 1 1

can we do this? :
A B F
0 0 0
1 0 0
0 1 0
1 1 1

i had a class test about this and i wrote the inverted one, but the teacher did not accept it? why? is there a certain way we have to do this?

thanks.

:S no its the same thing

 

[GriM ReapeR]

:S no its the same thing

i know right?? but the teacher said its wrong but she wouldn't explain?

 

[GriM ReapeR]

one morre thing.. "electrons always flow from lower potential to higher potential, i.e towards the more positive potential" will someone please explain?
thanks

 

[AAnsarii]

properties of wat?

just macroscopic properties at equilibrium
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w11_ms_31.pdf [Ans]4(a)

 

[AAnsarii]

In physics macroscopic properties ( as of what i know)
Are properties such as Density, Pressure (of Gases), Volume (of gases/liquids), Length (of solids) and Resistance (of wires) which change with change in temp (they could be measured, to measure temp. ex thermometer uses volume of mercury)

Hope this helped you

thanx a lot
so how is dis related to equilibrium?

 

[AAnsarii]

The number of Carbon-12 atoms in 12 grams of the substance is the mole.....and the avagadros constant is the number of atoms/molecules......

hw will C atoms b in d substance? can u plz xplain more?

 

[EpicLol]

i hope this is the one

1a: all gases so diffusion (F)
b: water needed so simple distillation (A)
c: identification of amino acids so chromatography (D)
d: iron filings insoluble so filtration (E)
e: crystals needed so evaporation (C)
f: liquid alkanes have bp so fractional distillation (B)

2ai: photosynthesis , in which chlorophyll traps sunlight and converts it to chemical energy.....

3ci :They are strongly bonded and so Its very hard to break the bonds between them
ii: As its ions are in layers which can slide over eachother

4aiii: As they have diff boiling points , lowest bp will be distilled first i.e cadmium then zinc then lead

5ai: metal + acid ---> salt + hydrogen
= so 2Li + 2HI ---> 2LiI +H2
ii: metal carbonate + acid ---> salt + CO2 +H2O
= s0 Zinc carbonate +Hydiodic acid ---> Zinc iodide + Carbondioxide + water
iii: Metal oxide+ acid ---> salt + water
= so MgO + 2HI ---> MgI2 + H2O
b: the first is redox as electrons are transfered (Li + 2H+ --->li+ +H2)<-- the ionic eqn
c: when chlorine is bubbled disblacement occurs as it is more reative than bromine and iodine
so hydriodic -->grey solid as iodine forms
hydrobromic ---> brown vapours as bromine forms

Thx a lot! I understand everything except the 5b.....even the third one loses and gains electons....why is it the first one?
Plz explain
Thx!

 

[thats_me]

just macroscopic properties at equilibrium
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w11_ms_31.pdf [Ans]4(a)

It's just the def of equilibrium u gota learn its just a ques of 2 marks , i think it means that conc, mass n volume all these things would not increase or dcrease in this state but its better u don go for all this if they ask for a defination write that ..

 

[EpicLol]

Thx a lot! I understand everything except the 5b.....even the third one loses and gains electons....why is it the first one?
Plz explain
Thx!

on the same paper could u help me with 7)a and b plz? I sort of understand but Im still confused....

 

[AAnsarii]

It's just the def of equilibrium u gota learn its just a ques of 2 marks , i think it means that conc, mass n volume all these things would not increase or dcrease in this state but its better u don go for all this if they ask for a defination write that ..

Thanks 4 making me stop wondering about d alien!!!

 

[EpicLol]

Does anyone have some questions that repeat quite often and think I should practice them? Plz post the paper and Q number plzplzplz
Thx I really need help revising like hard questions from past papers.....I suck at like the basics of chemistry....organic Im ok.....but like the general like colors, reactions, bases, alkalis I suck at those things...
Please help
Thanks!

 

[thats_me]

Thx a lot! I understand everything except the 5b.....even the third one loses and gains electons....why is it the first one?
Plz explain
Thx!

No the first one is a metal/acid reaction and has electron transfer where as the third one is metaloxide(which a base)/acid reaction ,and as far as i remmember the question stated that there are 2 acid base and one redox

 

[thats_me]

Thanks 4 making me stop wondering about d alien!!!

lol np

 

[Andyila1.2]

Please help me with these questions.. In an easy way

1. Describe bond breaking as endothermic and bond making as exothermic.
2.describe the production of heat energy by burning fuels
3.describe production of electrical energy from simple cells.

 

[EpicLol]

No the first one is a metal/acid reaction and has electron transfer where as the third one is metaloxide(which a base)/acid reaction ,and as far as i remmember the question stated that there are 2 acid base and one redox

so if the question said pick a redox reaction, then a or c would be correct?
Thx