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Chemistry and Physics AS paper 12 MCQS

syed1995

syed1995

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Sheikh Nahiyan

Sheikh Nahiyan

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goodluckayesha said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
how to do the 1st question??
Click to expand...

Lol.. What do I say! I logged in to see your post and after finishing the question in just 3mins, my internet connection was gone. Really sorry for replying late :p

The way I did it is like this:

50cm3 of H2O and calcium sulphate
1Ca ion is replaced by 2H ion

so, the reaction of KOH with the H2SO4 is:

H2SO4 + 2KOH --------> K2SO4 + 2H2O

no. of moles of KOH = (25 x 1.0x10^-2) / 1000 = 2.5x10^-4 mol

Stoichiometric ratio is 1:2
Therefore, no. of moles of sample solution is (2.5x10^-4)/2 = 1.25x10^-4

So,
1.25x10^-4 = (50x concentration)/1000

therefore, concentration = 2.5 x 10^-3 mol/dm3

So A is the answer :D
 
goodluckayesha

goodluckayesha

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Sheikh Nahiyan said:
Lol.. What do I say! I logged in to see your post and after finishing the question in just 3mins, my internet connection was gone. Really sorry for replying late :p

The way I did it is like this:

50cm3 of H2O and calcium sulphate
1Ca ion is replaced by 2H ion

so, the reaction of KOH with the H2SO4 is:

H2SO4 + 2KOH --------> K2SO4 + 2H2O

no. of moles of KOH = (25 x 1.0x10^-2) / 1000 = 2.5x10^-4 mol

Stoichiometric ratio is 1:2
Therefore, no. of moles of sample solution is (2.5x10^-4)/2 = 1.25x10^-4

So,
1.25x10^-4 = (50x concentration)/1000

therefore, concentration = 2.5 x 10^-3 mol/dm3

So A is the answer :D
Click to expand...
actually I got it already :D
 
Waleed Amjad

Waleed Amjad

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Sheikh Nahiyan said:
Mass of 1cm3 of H2O = 1g
no. of moles of H20 =( 1/18 ) = 1.33mol

Now, solve this using unitary method:
Volume of steam at 298K = 1.33
Volume of steam at 1K = (1.33) / 298
Therefore, Volume of steam at 596K = (1.33 x 596 )/ 298 = 2.6666... round off to 2.67. So answer is C
Click to expand...


If you follow the syllabus, there is a better way to find this.

By using the following equation. PV = nRT
where pressure is in Pascals, Volume is in m^3 , n = Moles, R is a constant which is 8.31 and Temperature in Kelvins (K)
Here water is 1 g/cm
So the number of moles will be 1 / mr = where mr of water (H2O) is 18, So 1/18 is the number of moles of water.

So to get the answer is simple.

PV = nRT
101000 x V = 1/18 x 8.31 x 596
V = ( 1/18 x 8.31 x 596) / 101000
V = 0.0027242904290429 m^3
Multiply the answer by 1000 to change m^3 to dm^3 this gives you = 2.72 which only shows similarity to option C ... Good luck.! the answer is a bit different because i used the R value as 8.31 , it might be different in the data booklet but 8.31 is also the closest value which has always worked for me. :)
 
Sheikh Nahiyan

Sheikh Nahiyan

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Waleed Amjad said:
If you follow the syllabus, there is a better way to find this.

By using the following equation. PV = nRT
where pressure is in Pascals, Volume is in m^3 , n = Moles, R is a constant which is 8.31 and Temperature in Kelvins (K)
Here water is 1 g/cm
So the number of moles will be 1 / mr = where mr of water (H2O) is 18, So 1/18 is the number of moles of water.

So to get the answer is simple.

PV = nRT
101000 x V = 1/18 x 8.31 x 596
V = ( 1/18 x 8.31 x 596) / 101000
V = 0.0027242904290429 m^3
Multiply the answer by 1000 to change m^3 to dm^3 this gives you = 2.72 which only shows similarity to option C ... Good luck.! the answer is a bit different because i used the R value as 8.31 , it might be different in the data booklet but 8.31 is also the closest value which has always worked for me. :)
Click to expand...

Didnt think of this method :p But you can do it both ways. As it is a MCQ you dont need to show your working :p That gives both the way to be correct :D THANKS THOUGH! :)
 
Sheikh Nahiyan

Sheikh Nahiyan

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Frankuzi said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
how to do question no 3 and 36?
Click to expand...

Answer for question 3 is C.

I know it is the answer but cannot exactly explain it to you right now. I need to study it more to explain it to you. But here is what I can give you for this moment:

"The size of an atom or ion depends on the size of the nucleus and the number of electrons. Generally atoms with higher numbers of electrons have larger radii than those with smaller numbers of electrons. Thus ions will have radii different from the atoms because ions will have either gained or lost electrons. The number of positive charges in the nucleus determines both the number of electrons that surround an atom and the number of electrons that can be lost or gained to form ions.
  • Thus as the charge on the ion becomes more positive, there will be less electrons and the ion will have a smaller radius.

  • As the charge on the ion becomes more negative, there will be more electrons and the ion will have a larger radius.

  • As the atomic number increases in any given column of the Periodic Table, the number of protons and electrons increases and thus the size of the atom or ion increases."






 
Sheikh Nahiyan

Sheikh Nahiyan

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Frankuzi said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
how to do question no 3 and 36?
Click to expand...

As for this question. The answer: I am getting to it.

1. is correct. This is because the increase in surface area will not increase the amount of nitrogen oxides released, instead lessen it as the amount of exhaust gases passing through it will be converted quicker.

2. is wrong because you are increasing the concentrations of the reactants, and so the concentration of nitrogen oxide is going to increase. We cannot take this option as an answer.

As 2 is not taken, there is no other possible combination and so the answer is D
 
Frankuzi

Frankuzi

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Sheikh Nahiyan said:
Wish I could explain it to you now.. Got an exam tomorrow.. Nai kar sakta today.. I did this paper long time ago. Need to study it again :L
Click to expand...
For Q.17 is actually very simple. (A) can occur because NH3 can be a base and SO3 can be an acid. (B) is also correct because in this reaction, ammonium salt is formed where ammonium itself involved dative covalent bond. (C) is correct because NH4+ and SO42- to give (NH4+)2SO4 which can be considered as Ionic bond formation.
Since A,B and C are out, that leaves you with D.
 
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