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Physics, Chemistry and Biology: Post your doubts here!

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Chemistry:
Q: Suggest a reson 4 only 'roughly' twice as much hydrogen gas being produced at the cathode as oxygen gass at the anode in the electrolysis of water.
Q: During da electrolysis of molten aluminium chloride (AlCl3) the carbon anodes r burned away. Explain why dis shud hapen n write a balanced chemical equation 4 da reactions dat take place.
Thanx!
for your first answer you have to consider the fact that all moles occupy the same volume at rtp and the ratio of hydrogen to oxygen is 2:1 , for that exact reason there is twice as much hydrogen than oxygen. Just use water as an example
 
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I need help !!!!!!!^^^
esters are made from--
1)carboxylic acid and
2)alcohol
wen u name an ester first u write the name of the carboxylic acid used and then the alcohol used.
so in propyl ethanoate...the alcohol is PROPANOL(3 carbon atoms-C3H7OH) and the carboxylic acid used is ETHANOIC ACID(2 carbon atoms-CH3COOH
C3H7OH(aq) + CH3COOH (AQ)------>CH3CO2C3H7(aq) + H2O (l)
for help in naming-- the part before COOH in the ester is the carboxylic acid part part....n what is after it is the alcohol part.

CH3CO2C3H7 ----- > ethanoate (carboxylic acid part)
---->propyl (alcohol part)
structure is--> http://www.docbrown.info/page15/Image1694.gif
i hope it helps..:D
 
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esters are made from--
1)carboxylic acid and
2)alcohol
wen u name an ester first u write the name of the carboxylic acid used and then the alcohol used.
so in propyl ethanoate...the alcohol is PROPANOL(3 carbon atoms-C3H7OH) and the carboxylic acid used is ETHANOIC ACID(2 carbon atoms-CH3COOH
C3H7OH(aq) + CH3COOH (AQ)------>CH3CO2C3H7(aq) + H2O (l)
for help in naming-- the part before COOH in the ester is the carboxylic acid part part....n what is after it is the alcohol part.

CH3CO2C3H7 ----- > ethanoate (carboxylic acid part)
---->propyl (alcohol part)
structure is--> http://www.docbrown.info/page15/Image1694.gif
i hope it helps..:D
ohh srry i didnt see the later part
thats simple actually....diff between d 2 is dat one is saturated(with no C=C double bonds) d other is unsaturated (with one or more C=C double bonds)..this u will by seeing the no of h atoms..jisme zaada hai...that is saturated ..jisme kam hai wo unsaturated hai...or u can draw the diagram n check for urself:D
diff between saturated n unsaturated is given by the BROMINE WATER TEST...add bromine water to them
UNSATURATED OIL WILL DECOLOURIZE THE BROMINE WATER....i.e. brown colour of bromine will disappear
and saturated wala will remain ythe same:)
in Civ ----it is a kind of hydrolysis in which u get the reactants back ---a sodium salt is formed (of the carboxylic acid) and alcohol or u can write glycerol
 
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ohh srry i didnt see the later part
thats simple actually....diff between d 2 is dat one is saturated(with no C=C double bonds) d other is unsaturated (with one or more C=C double bonds)..this u will by seeing the no of h atoms..jisme zaada hai...that is saturated ..jisme kam hai wo unsaturated hai...or u can draw the diagram n check for urself:D
diff between saturated n unsaturated is given by the BROMINE WATER TEST...add bromine water to them
UNSATURATED OIL WILL DECOLOURIZE THE BROMINE WATER....i.e. brown colour of bromine will disappear
and saturated wala will remain ythe same:)
in Civ ----it is a kind of hydrolysis in which u get the reactants back ---a sodium salt is formed (of the carboxylic acid) and alcohol or u can write glycerol
thanks a lot ...........:D
(y) (y)
 
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please help , this question i dont know the answer, please tell the answer and tell my why. suggest a condition, in terms of tempreture and pressure, which would give high yield of methanol.
 
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plzzzz can anyone hepl me with this question!!!!!!!!!!!!!!!!!!
 

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plzzzz can anyone hepl me with this question!!!!!!!!!!!!!!!!!!

2 a) Weight = mass * gravitational field strength. ------> W = 5.4 * 10 = 54 N

b i) the point where proportionality between force/weight and extension/Hooke’s Law stops .
[Limit of proportionality is the point which if exceeded, the spring extension will no longer be proportional to the load. --->http://greennotes.com.sg/effects-of-forces/]

ii 1) We know F = kx ---> F = weight of the full bucket ie = 54 N, x = extension of the spring (35 - 20) = 15 cm , k = constant
So, k = F/x = 54/15 = 3.6

Now, x = (25 - 20) = 5 cm.
So, F =kx = 3.6 * 5 = 18 N.

2) Force without oil = 18 N
So, force exerted by oil = 54 - 18 = 36 N
W = mg -----> m = W/g = 36/10 = 3.6 kg

Hope u gt it!!
:D
 
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2 a) Weight = mass * gravitational field strength. ------> W = 5.4 * 10 = 54 N

b i)the point where proportionality between force/weight and extension/Hooke’s Law stops .
[Limit of proportionality is the point which if exceeded, the spring extension will no longer be proportional to the load. --->http://greennotes.com.sg/effects-of-forces/]

ii 1) We know F = kx ---> F = weight of the full bucket ie = 54 N, x = extension of the spring (35 - 20) = 15 cm , k = constant
So, k = F/x = 54/15 = 3.6

Now, x = (25 - 20) = 5 cm.
So, F =kx = 3.6 * 5 = 18 N.

2) Force without oil = 18 N
So, force exerted by oil = 54 - 18 = 36 N
W = mg -----> m = W/g = 36/10 = 3.6 kg

Hope u gt it!!
:D

2 a) Weight = mass * gravitational field strength. ------> W = 5.4 * 10 = 54 N

b i)the point where proportionality between force/weight and extension/Hooke’s Law stops .
[Limit of proportionality is the point which if exceeded, the spring extension will no longer be proportional to the load. --->http://greennotes.com.sg/effects-of-forces/]

ii 1) We know F = kx ---> F = weight of the full bucket ie = 54 N, x = extension of the spring (35 - 20) = 15 cm , k = constant
So, k = F/x = 54/15 = 3.6

Now, x = (25 - 20) = 5 cm.
So, F =kx = 3.6 * 5 = 18 N.

2) Force without oil = 18 N
So, force exerted by oil = 54 - 18 = 36 N
W = mg -----> m = W/g = 36/10 = 3.6 kg

Hope u gt it!!
:D
got it thank u so much!!!!!!!!
 
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Hey does anyone have markscheme for physics 1993 paper 3 ?
its really hard and weird, is it a good idea to solve it, or what other papers should i do for practice ? :s
 
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i have a question regarding chemistry, most compounds dissolve more in hot water than in cold , is it possibly because there'll be more evaporation so more space for the other particles to dissolve but isnt it like the water will evaporate as well if we heat it? so actually it wont be enough to dissolve other particles as well -__-. correct me if im wrong, i just dont get it :(
 
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i have a question regarding chemistry, most compounds dissolve more in hot water than in cold , is it possibly because there'll be more evaporation so more space for the other particles to dissolve but isnt it like the water will evaporate as well if we heat it? so actually it wont be enough to dissolve other particles as well -__-. correct me if im wrong, i just dont get it :(
they absorb more heat energy from the hot water
 
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so like it will do sumthin to their bonds? perhaps make it weaker? so it dissolves more?
compounds 'dissolve' in the first place as a result of a reaction with the water,Because molecules move faster with high temperature (the energy they get from the water) they collide more, and more reaction occurs which gets faster as a result of the energy they get. it keeps reacting till its fully dissolved, but faster in hot water than cold water. :)
 
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can u please tell me what topics from physics come in the ATP paper? (O-level) like in chemistry its mainly just Acids, Bases n Salts , Rate of reaction and Moles..
PLEASE HELP!
 
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