Biology; Chemistry; Physics: Post your doubts here!

[Saad Mughal]

doesn't acid have water? will it evaporate the water in it.
man think about it. it will add more H+ ions so our results will be inaccurate.
CIE is not god, neither are our teachers. my chemistry teachers say what they read in books, especially when he has no answer to it.


i read the question, it's answer, comment on answer as well through redspot. when nothing made sense then i decided what i said.

usama321 TheLeagueofShadows

Ok, so I have read both points of the argument. My final evaluation of the problem would be:
The purpose of titration is to find the concentration as accurately as possible. We use the water to clean the burette of any impurities and unwanted substances. The use of water however, leaves some water in the burette, this means that when we will put our solution (here the acid) into the burette, the water affined to the burette will DILUTE the solution that is put in, this means that the concentration WILL BE AFFECTED which will, in terms, make the titration useless. To counter this problem, we use the acid to rinse the burette, now the reason for this is that the acid that we use to rinse, will be diluted by the water and hence, the extra water affined to the burette will be rinsed through with the acid, this will give us a clean, pure burette suitable for experiment. Water to remove impurities and unwanted substances, the rinsing with the solution, to remove excess water attached to the beaker.
I maybe wrong, but I'm giving, from my understanding, the justification of what CIE says.

 

[usama321]

PHEW AT LAST SOME LOGICAL APPROACH. Seems logical enough to me. Still, lets confirm it from some teacher before storing it in our brains

 

[Saad Mughal]

Suchal Riaz usama321 TheLeagueofShadows
This is a forum for open discussion and help, if one person has one view and the other has one view, please try to reach mutual consensus on the matter instead of blaming or criticizing each other. That's the purpose of this thread!
But I do agree with Suchal Riaz on the matter that some annoying stupid things does make a person lose his tempo.

 

[Suchal Riaz]

usama321 TheLeagueofShadows

Ok, so I have read both points of the argument. My final evaluation of the problem would be:
The purpose of titration is to find the concentration as accurately as possible. We use the water to clean the burette of any impurities and unwanted substances. The use of water however, leaves some water in the burette, this means that when we will put our solution (here the acid) into the burette, the water affined to the burette will DILUTE the solution that is put in, this means that the concentration WILL BE AFFECTED which will, in terms, make the titration useless. To counter this problem, we use the acid to rinse the burette, now the reason for this is that the acid that we use to rinse, will be diluted by the water and hence, the extra water affined to the burette will be rinsed through with the acid, this will give us a clean, pure burette suitable for experiment. Water to remove impurities and unwanted substances, the rinsing with the solution, to remove excess water attached to the beaker.
I maybe wrong, but I'm giving, from my understanding, the justification of what CIE says.

would not it add more H+ ions affecting concentration
and there are dozens of questions for which this is said to be an error due to which the result of an experiment was wrong. i can show u many questions.

 

[Saad Mughal]

would not it add more H+ ions affecting concentration
and there are dozens of questions for which this is said to be an error due to which the result of an experiment was wrong. i can show u many questions.

I'm not saying I'm correct. Errors are going to be introduced in both ways, but leaving water as is will, according to what I know, bring a larger error.
The acid in a way washes away the water (the water makes the acid more dilute becoming part of the acid) when we rinse with it, therefore, after several rinses, there is no water nor acid remaining since the water is rinsed by the acid! That's what I know.
Best way to be error-free is to just go and buy a new clean burette. Problem solved.

 

[Suchal Riaz]

I'm not saying I'm correct. Errors are going to be introduced in both ways, but leaving water as is will, according to what I know, bring a larger error.
The acid in a way washes away the water (the water makes the acid more dilute becoming part of the acid) when we rinse with it, therefore, after several rinses, there is no water nor acid remaining since the water is rinsed by the acid! That's what I know.
Best way to be error-free is to just go and buy a new clean burette. Problem solved.

man doesn't acid contain water? my parents are wondering why i m laughing alone in my room
first error intact, another added. water still in container but further H+. even bigger error. better wash from water than let it dry. u can wach from petrol or other volatile liquid which will evaporate very quickly.

 

[Saad Mughal]

man doesn't acid contain water? my parents are wondering why i m laughing alone in my room
first error intact, another added. water still in container but further H+. even bigger error. better wash from water than let it dry. u can wach from petrol or other volatile liquid which will evaporate very quickly.

Acid contains water. Adding more water to it makes it dilute, you agree, right?
The water present in the burette is rinsed by the acid. The acid mixes with the water in the burette during rinsing; on the addition of the water in the burette the acid becomes more dilute hence removing the water.
Rinsing with acid is a better option since this will bring about a smaller error in the concentration whereas the water itself (if left in burette) will bring about a relatively larger error.
I've already told you. I'm not very good at chemistry but I have my concepts. Please don't break them.

 

[usama321]

A certain quantity of electricity liberates 9 g of aluminium. The mass of copper liberated from copper(II) sulfate
solution (Cu2+
ions) by the same quantity of electricity is: (Relative atomic masses: Al = 27; Cu = 64)
A 9.0 g
B 21.33 g
C 32.0 g
D 42.67 g
E 64.0 g
Anyone.. Help please!!
Agar is ka ans kisi ko aagaya wo BAAP hai

seems like C to me due to the fact that Cu should require less electricity as it is +2, compared to +3. So,
(64/3)/2 *3 = 32. Do tell the answer if you know it

 

[Suchal Riaz]

Acid contains water. Adding more water to it makes it dilute, you agree, right?
The water present in the burette is rinsed by the acid. The acid mixes with the water in the burette during rinsing; on the addition of the water in the burette the acid becomes more dilute hence removing the water.
Rinsing with acid is a better option since this will bring about a smaller error in the concentration whereas the water itself (if left in burette) will bring about a relatively larger error.
I've already told you. I'm not very good at chemistry but I have my concepts. Please don't break them.

ohh u mean 'now it makes SOME sense, let it be'
okay okay i wont stop u.
but still the acid wont be removed from burrette either, just the way whole water wont be. no matter how much time u rinse it, u will add more dilute acid, when u spill it out some of it will stick to sides. maybe it still has less error but i know many times in past paper that washing burrette ot flask by alkali/acid is mentioned as error. nobody can deny it.
forget about it. leave it. CIE makes mistakes and we justify them, they dont.

 

[Saad Mughal]

seems like C to me due to the fact that Cu should require less electricity as it is +2, compared to +3. So,
(64/3)/2 *3 = 32. Do tell the answer if you know it

Exactly! I calculated it the same way. As I've mentioned above, C should be the answer!

 

[asma tareen]

mmm if u ppl dont mind am i allowed to ask my querries ??

 

[Saad Mughal]

ohh u mean 'now it makes SOME sense, let it be'
okay okay i wont stop u.
but still the acid wont be removed from burrette either, just the way whole water wont be. no matter how much time u rinse it, u will add more dilute acid, when u spill it out some of it will stick to sides. maybe it still has less error but i know many times in past paper that washing burrette ot flask by alkali/acid is mentioned as error. nobody can deny it.
forget about it. leave it. CIE makes mistakes and we justify them, they dont.

We never wash out flasks with acids/alkalis. We only rinse burettes with the solution to remove the water, we rinse it several times, and we reduce the error as far as we can! Excess solution of the acid in the burette is not an impurity, water is.

 

[Saad Mughal]

mmm if u ppl dont mind am i allowed to ask my querries ??

Please do. So we can get off the current topic as well.

 

[asma tareen]

Please do. So we can get off the current topic as well.

thnx
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s11_qp_22.pdf
q2 (a) i seriously dont get these energy conversions

 

[usama321]

thnx
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s11_qp_22.pdf
q2 (a) i seriously dont get these energy conversions

I think it should be chemical energy from the body, to kinetic energy as the bike moves, and gravotational potential energy as the bike gains height which in turn once again turns to kinetic energy downhill, and heat energy (friction of tyres ), and sound perhaps too?

 

[asma tareen]

I think it should be chemical energy from the body, to kinetic energy as the bike moves, and gravotational potential energy as the bike gains height which in turn once again turns to kinetic energy downhill, and heat energy (friction of tyres ), and sound perhaps too?

thnx i got it

 

[Saad Mughal]

thnx
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s11_qp_22.pdf
q2 (a) i seriously dont get these energy conversions

Key word here is CONSTANT SPEED that means kinetic energy remains the same throughout.
Now, the cyclist has CHEMICAL ENERGY in the body that is used to pedal the bicycle, this chemical energy is converted to kinetic and gravitational potential energy, the kinetic energy is constant, the gravitational potential energy (converted from chemical energy) is increasing (with height). Some of the energy in the body is being lost as thermal energy because of the friction between the tyres and the hill (excess chemical energy being wasted as thermal energy).

 

[Saad Mughal]

I think it should be chemical energy from the body, to kinetic energy as the bike moves, and gravotational potential energy as the bike gains height which in turn once again turns to kinetic energy downhill, and heat energy (friction of tyres ), and sound perhaps too?

They've asked only for uphill so, chemical energy ---> kinetic energy + gravitational potential energy + some heat energy.

 

[usama321]

Key word here is CONSTANT SPEED that means kinetic energy remains the same throughout.
Now, the cyclist has CHEMICAL ENERGY in the body that is used to pedal the bicycle, this chemical energy is converted to kinetic and gravitational potential energy, the kinetic energy is constant, the gravitational potential energy (converted from chemical energy) is increasing (with height). Some of the energy in the body is being lost as thermal energy because of the friction between the tyres and the hill (excess chemical energy being wasted as thermal energy).

thanks for pointing that out. guess i have to be more careful

 

[Suchal Riaz]

thnx i got it

as she pedals up, the speed is constant so main changes are from chemical to gravitaional potential energy with some of it wasted in internal energy/ or heat energy. no kinetic because the speed is constant.