Biology; Chemistry; Physics: Post your doubts here!

[Dream.Eater]

Well, I'm not thinking about writing irrelevant material. For example, if examiner asks about the TEST OF NITRATE IONS, many of the candidates will write this:
"ADD AQUEOUS SODIUM HYDROXIDE THEN ADD ALUMINUM FOIL; WARM CAREFULLY: AMMONIA PRODUCED "
Whereas, I would write this:
"ADD CONCENTRATED HYDROCHLORIC ACID, THEN ADD FRESHLY PREPARED IRON (II) SULPHATE> : BROWN RING FORMS."

It's just an example. I know that this test is not the part of syllabus, but is definitely correct. Just like this,, there are many things!! mhamzasiddiqui

I completely agree with Awesome12. But, personally I don't feel there's a need to write material beyond the scope of the 5070 syllabus. It thinks its best if you just study all the syllabus requirements as perfectly as you can and practice as many past papers as you can. After all, the examiners don't expect you to know concepts that are not in the syllabus. But anyway this is just my two cents....

 

[Dark Destination]

To all lovely people here, I am really concerned about your honest replies on my question which I want to ask.
I am going to appear in May/June 2014 for Chemistry 5070. Alhamdullilah, I am passionate about getting a distinction in O level Chemistry. It has been my favourite subject and will be in the future. I have a sound knowledge of all the reactions, processes and QUALITATIVE ANALYSIS. Apart from the syllabus requirement for Chemistry, I have also a fine knowledge of tests which, however, are not a part of the syllabus. So moving on to my question, I want to ask if it is alright for me to write down that material which are not a part of syllabus though, but are legitimate? And this can lead me to have a distinction? Or what else I need to do in this petite amount of time to get myself prepare for DISTINCTION>>? I will be very happy to have your views on my question. Thank you, mhamzasiddiqui!

I don't think that is necessary. Stick to the required details for O-Level Chemistry.
Your answer might be right, but the examiner will be looking at the marking scheme, and if the marking scheme doesn't have that point, it might cause hindrance for the examiner. Even if you get the mark, it will be equal to the person who wrote the normal test, or a normal answer specified in the marking scheme.

Also, not everyone gets full marks. Get full marks, and you have your distinction. That's it.

 

[Dark Destination]

Saw this question in the past papers of Chemistry.

Q. Carbon Monoxide has a triple covalent bond. Draw the structure of Carbon Monoxide.

We only have to show the outer shell electrons. How will we draw this?

 

[zaka ullah]

Saw this question in the past papers of Chemistry.

Q. Carbon Monoxide has a triple covalent bond. Draw the structure of Carbon Monoxide.

We only have to show the outer shell electrons. How will we draw this?

you can consult chemistry revision section in the xtreme papers.that would be very helpful.

 

[Dream.Eater]

Saw this question in the past papers of Chemistry.

Q. Carbon Monoxide has a triple covalent bond. Draw the structure of Carbon Monoxide.

We only have to show the outer shell electrons. How will we draw this?

That question is the toughest question on covalent bonds from all the previous Chem papers. Its done like this.
Now, oxygen has a valency of 6, carbon has 4. In the triple covalent bond 6 electrons( two pairs) must be shared. Moreover both oxygen and carbon must have an octave of electrons after bonding. So, oxygen is forced to share two pairs(4 ) of electrons in the bond while carbon shares only a pair(2) of electrons. So a triple covalent bond is formed and the octave of both are satisfied. This covalent bond has a special name which I seem to have forgotten sadly.....
Anyway this is beyond the scope of our syllabus and was really unfair by Cambridge since its worth 2 marks.
Just draw the dot and cross diagram based on the info I have mentioned and you should be able to sort-of understand it

 

[Awesome12]

Saw this question in the past papers of Chemistry.

Q. Carbon Monoxide has a triple covalent bond. Draw the structure of Carbon Monoxide.

We only have to show the outer shell electrons. How will we draw this?

 

[Dark Destination]

That question is the toughest question on covalent bonds from all the previous Chem papers. Its done like this.
Now, oxygen has a valency of 6, carbon has 4. In the triple covalent bond 6 electrons( two pairs) must be shared. Moreover both oxygen and carbon must have an octave of electrons after bonding. So, oxygen is forced to share two pairs(4 ) of electrons in the bond while carbon shares only a pair(2) of electrons. So a triple covalent bond is formed and the octave of both are satisfied. This covalent bond has a special name which I seem to have forgotten sadly.....
Anyway this is beyond the scope of our syllabus and was really unfair by Cambridge since its worth 2 marks.
Just draw the dot and cross diagram based on the info I have mentioned and you should be able to sort-of understand it

How did you know then?

I was drawing the structure, and wasn't able to understand why oxygen had 9 electrons in its outer shell.

So why are they questioning material that is out of the scope of our syllabus?

 

[Dark Destination]

Advantages and disadvantages of recycling metals?

And what are we required to know about the Hydrogen-Oxygen fuel cell? :/

 

[Awesome12]

Advantages and disadvantages of recycling metals?

And what are we required to know about the Hydrogen-Oxygen fuel cell? :/

learn the anode and cathode reactions occuring in the fuel cell. Learn the advantages and disadvantage of it. If you have Fundamental Chemistry, the author has thoroughly discussed this topic

 

[Dream.Eater]

How did you know then?

I was drawing the structure, and wasn't able to understand why oxygen had 9 electrons in its outer shell.

So why are they questioning material that is out of the scope of our syllabus?

I too may have attempted the question in the same way you did. After countless failed attempts, i asked my chem teacher who explained the answer and told me everything that i told you in my previous post.
I think cambridge gave this as problem-solving and critical thinking question which would have pushed the candidates to their limits especially under the time pressure. But, hopefully we dont get a question like this in our
exam.
Anyway, i hope you understood my explanation

 

[Dream.Eater]

Advantages and disadvantages of recycling metals?

And what are we required to know about the Hydrogen-Oxygen fuel cell? :/

Advantages of recycling
1. Metal ores are finite so recycling helps to conserve them.
2. Less energy consuming.
3. More eco-friendly since its less polluting and more energy saving.

Disadvantages
1. There is a need to collect the waste metals and separate them.
2. Purification maybe needed at the end of the recycling process

 

[funky brat]

Guys can anybody explain this MCQ? I really don't get it. MCQ number 3.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w03_qp_1.pdf

 

[funky brat]

another question

View attachment 37472

I know the answer is B, but what if the size of force acting on the ground was equal to the weight of the stone, then what would happen? Is that even possible? And how exactly are 2 forces simultaneously acting from the object?

Okay, this might be very late and you already know the answer but I would just like to give my opinion since I selected the right option the first time I saw this. In this MCQ they are talking about a ball hitting a ground therefore we can assume that the ball was at a height before it hit the ground. The ball has a force due to it's weight but there's another force because of the height. See if you are standing and an object is dropped on your head from a height you feel a greater impact than you would have felt it is was just put over your head. Therefore there's just more than the weight of the object. Again this is just an opinion, I might sound very stupid. But since everybody is confused over this so yeah. And the force is definitely downwards therefore the answer is B.

 

[Gohar Awais]

IN pyhsics, Hooke's Law states that F=ke meaning stress is directly proportional to strain within an elastic limit, is there a unit for the constant (k)? and also is there a fixed measurements for the force and extension as that like in the formula F=ma -----> W=mg and Mass is neccessary to be in kilos while W in Newtons so for F=ke to bring your measurements to metres and newtons?

 

[Gohar Awais]

Guys can anybody explain this MCQ? I really don't get it. MCQ number 3.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w03_qp_1.pdf

Look, first of all u must know in mind that hydrogen has a Mr of 2 in H2 gas and this is less than the average Mr of Air which is 30 so it will diffuse faster than air. With this clear, the porous pot acts as a membrane between the two gases. Hydrogen is less dense than air and diffuses rapidly through the porous pot as compared to air. The pressure is increased as vacuum is created in the space occupied by H2 gas and the air takes up on this space(it takes up on the space very slowly due to its higher Mr which is 15 times higher than H2 gas), as a result of the pressure water level at X is pushed down and it will remain down. SO the appropriate answer is B.

 

[funky brat]

IN pyhsics, Hooke's Law states that F=ke meaning stress is directly proportional to strain within an elastic limit, is there a unit for the constant (k)? and also is there a fixed measurements for the force and extension as that like in the formula F=ma -----> W=mg and Mass is neccessary to be in kilos while W in Newtons so for F=ke to bring your measurements to metres and newtons?

Umm I think the unit for k would be the same as for extension, which depends extension is in mm or cm. Since k is a constant so it is the proportion by which the length of the spring increases. And yeah force is taken in Newtons and and extension mostly in cm but you can do your calculations according to the requirements of the question.

 

[funky brat]

Look, first of all u must know in mind that hydrogen has a Mr of 2 in H2 gas and this is less than the average Mr of Air which is 30 so it will diffuse faster than air. With this clear, the porous pot acts as a membrane between the two gases. Hydrogen is less dense than air and diffuses rapidly through the porous pot as compared to air. The pressure is increased as vacuum is created in the space occupied by H2 gas and the air takes up on this space(it takes up on the space very slowly due to its higher Mr which is 15 times higher than H2 gas), as a result of the pressure water level at X is pushed down and it will remain down. SO the appropriate answer is B.

Thanks but I didn't get the last line and hence the reason behind the answer, mind explaining it again please?

 

[Awesome12]

Guys can anybody explain this MCQ? I really don't get it. MCQ number 3.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w03_qp_1.pdf

H2 is less dense than air. As a result, it will diffuse from the surrounding in to the porous pot at a faster rate. As a result, it will exert pressure, causing the liquid level at X to drop and stay at a lower level

 

[Gohar Awais]

Thanks but I didn't get the last line and hence the reason behind the answer, mind explaining it again please?

for the rate of diffusion there are some factors:
temperature and is directly proportional i.e. makes it faster
pressure, and is inversely proportional i.e makes it slower higher pressure slow diffusion
Mr , this varies. at petrol station there is CNG compressed under a increased pressure than room pressure.
It occupies less space as compared to the same amount in r.t.p so
when pressure increases the water level at X will decrease because the more pressure the less space a liquid/gas will occupy.
water level will remain less as air from the surroundings will also enter the gas jar and occupy all the space left by the air in porous pot

 

[Dark Destination]

Thanks but I didn't get the last line and hence the reason behind the answer, mind explaining it again please?

Isn't the answer A?