Biology; Chemistry; Physics: Post your doubts here!

[TheLeagueofShadows]

Q3,22 and 37. Please with explanation.
http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s03_qp_1.pdf

 

[ZaqZainab]

why should it be at the right of c

If you hold it from D it will stay still
the point D is Thicker More weight on D side
Lets take an example a irregular object and place its middle on a pivot (you might not have that at home use an eraser) and see the way it is place a object on the part which goes up see it balancing and then hold(with your figures) the object from the part were the object was not kept you will see that it won't move that is what is know by the center of mass
This is all practical you see

 

[hafsa saleem]

thnx

If you hold it from D it will stay still
the point D is Thicker More weight on D side
Lets take an example a irregular object and place its middle on a pivot (you might not have that at home use an eraser) and see the way it is place a object on the part which goes up see it balancing and then hold(with your figures) the object from the part were the object was not kept you will see that it won't move that is what is know by the center of mass
This is all practical you see

 

[ZaqZainab]

Q3,22 and 37. Please with explanation.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s03_qp_1.pdf

Question 22 only acids react with Bases and Sodium hydroxide is a base and near 7 means 6 weak acid or 8 weak base
answer will be weak acid!
Question 37
C_H_+502--> CO2+H20
BALANCE oxygen
C_H_+5O2->3CO2+4H2O
NOW GLANCE THE C AND H

you should have 3 C AND AND 8 H as 4*2= 8
I dunno about 3 sorry can't think now have got Bio exam tomorrow

 

[ZaqZainab]

thnx

I know you did not understand i am so sorry really bad at explaining

 

[hafsa saleem]

I know you did not understand i am so sorry really bad at explaining

never mind at least u helped

 

[hafsa saleem]

can any angel help me answering Q9b)ii) of the following paper
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_22.pdf

 

[hafsa saleem]

plzzzzzzzzzzzz people help !!!!!!!!!!!!!!I have just got a couple of hours before the breathtaking moment is about to start.

 

[Hskk]

can any angel help me answering Q9b)ii) of the following paper
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_22.pdf

At the surface the volume has increased. Due to the increase in volume the molecules have more space to move about i.e. they are further apart so there are less frequent collision between the molecules and the surface of balloon so pressure is low.

And what do you mean couple of hours? Physics paper is next week

 

[hafsa saleem]

I m a student of o1 so I m talking about my school exams.thnx for the answer

 

[hafsa saleem]

At the surface the volume has increased. Due to the increase in volume the molecules have more space to move about i.e. they are further apart so there are less frequent collision between the molecules and the surface of balloon so pressure is low.

And what do you mean couple of hours? Physics paper is next week

can u help me understand why volume of the air inside the balloon decreases at the surface?

 

[Hskk]

can u help me understand why volume of the air inside the balloon decreases at the surface?

Ohhh!! I panicked for a while there.
It doesn't decrease, it INCREASES, basically the pressure on the outside decreases, when the balloon was in the water, lots of particles were hitting the outside surface of the balloon so it's volume was less, when the balloon had risen up to the surface, less particles were hitting the balloon from the outside so the inside particles were able to move further apart thus the volume of the balloon increased. Its a very monotonous explanation, I hope you got it.

 

[TheLeagueofShadows]

Question 22 only acids react with Bases and Sodium hydroxide is a base and near 7 means 6 weak acid or 8 weak base
answer will be weak acid!
Question 37
C_H_+502--> CO2+H20
BALANCE oxygen
C_H_+5O2->3CO2+4H2O
NOW GLANCE THE C AND H

you should have 3 C AND AND 8 H as 4*2= 8
I dunno about 3 sorry can't think now have got Bio exam tomorrow

Thanks!

 

[Ghada Tahraoui]

Heyy, good luck for evryone's Bio today kaaayyyyyyy

 

[Buland Iqbal]

Heyy, good luck for evryone's Bio today kaaayyyyyyy

But we don't have bio today

 

[Saad Mughal]

Q3,22 and 37. Please with explanation.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s03_qp_1.pdf

For questions like 3, where you have a reaction with which you are not familiar. Try elimination. Let's discuss this shall we,
For option A, Zn + 2HCl --> ZnCl2 + H2, Hydrogen won't change the colour of the litmus so option A rejected.
For option B, Na2CO3 + 2HCl ---> 2NaCl + H2O + CO2, Carbon dioxide (the only gas) is an acidic oxide so it won't change the litmus (since it's already red), option B rejected,
For option C, NaOH + NH4Cl ---> NaCl + H2O + NH3, Ammonia is an alkaline gas so it won't have any affect on the BLUE litmus paper. So Option C rejected.
Hence, since all others are rejected, it must be option D.
P.S. The first three reactions are all KNOWN reaction so you can easily determine their products.

For question 22, Don't go for the colour, it doesn't tell you anything. Look at the line where it says that 'the gas is readily absorbed in sodium hydroxide', that tells you that it is an acidic gas. Now, since they have mentioned that the pH is close to 7 (weak acid or weak alkali) then you can easily pick out option C as being correct. An acidic gas with a high pH.

For question 37,
It's just like balancing a equation, just remember that like we've learnt in ratios (for moles), that mole-mole ration and volume-volume ratio tells us about how much each substance is reacting;
CH4 + 5O2 ---> 2H2O + CO2 (rejected, not balanced).
C2H6 + 5O2 ---> 3H2O + 2CO2 (rejected, not balanced).
C3H8 + 5O2 ---> 4H2O + 3CO2 (viola! your answer!).
C4H10 + 5O2 ---> 5H2O + 4CO2 (rejected, not balanced).
Always use the hydrogen and carbon to determine the products, it's a lot quicker.

Hope that helps!

 

[Mohammad Mishal]

saad mughal brilliant explanation!

 

[Saad Mughal]

saad mughal brilliant explanation!

 

[pikachu]

What are the advantages and disadvantages of nylon and polyester?

 

[usama321]

What are the advantages and disadvantages of nylon and polyester?

well advantages in the sense of usages. Well they are used in clothing, plastics, ropes etc just google some more uses if you want

disadvantages will include that they are non biodegradable, don't dissolve so cause pollution in water, have to be buried which takes up space etc