Chemistry: Post your doubts here!

[Namehere]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_1.pdf Question 10 can anyone help me please

Here you need to know two concepts/formulas:
mole fraction = number of moles of molecule A / total number of moles
Partial pressure of A = mole fraction of A x total pressure

If 20% of steam had been converted to hydrogen and oxygen, there must be 80% of steam left. So, if you before had 1 mole of steam, you now have 0.8 moles of steam (80% of 1.). Because of the 2:2:1 ratio in the equation, 2H2O ---> 2H2 + O2 , if 0.2 moles of steam had been converted into its products, then by simple stoichiometry the change for H2 is +0.2 and for O2 +0.1.

So you now have the moles of each substance present at equilibrium. If you now use the formulas from the beginning, to calculate the partial pressure, you would see you need the mole fraction of your gas and the total pressure. So, mole fraction = number of moles of molecule A / total number of moles

For steam, you have 0.80 moles, for H2 0.20 and for O2 0.10. If you add them up this give 1.1 - the total number of moles. Therefore, the mole fraction of steam is 0.80/1.1, for H2 is 0.20/1.1 and for O2 is 0.10/1.1. To get the partial pressure of each gas you now times the mole fraction of each substance by the total pressure at which the experiment is done - 1 atm. Hence for steam the partial pressure is 0.8 x 1 / 1.1 and so on...

Hope it helps.

 

[Abdel Moniem]

Thank you so much

 

[hellangel1]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
please please someone help with Q4 biii
Pleasee!

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf
Question 34

 

[Namehere]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf
Question 34

The answer is B. 1 is correct for the obvious reason that OH- from the first eq (equilibrium) and H+ from the second eq would react to make H2O, leading to the position of the eq of the first eq to shift to the right, increasing the solubility of hydroxyapatite. 2 is also correct because from the second eq the phsophate ion would react with the proton, which leads to a decrease in phosphate ions. This has to be compensated and in the first eq the equilibrium shifts to the right to restore the phosphate ions, leading to an increase in solubility of hydroxyapatite once again. 3 is wrong because the statement "calcium ions react with acids" is wrong. Calcium reacts with acids, Calcium ions, however, do not (the Ca2+ ion already has its full outer shell complete and is happy as it is).

Hope this helps.

 

[Igcse stuff]

once you solve the past pprs from 2004-2012 then u can easily score 30-36 marks easily in that ....
P1 P2 P4 ...score max marks then u can easily get an A*

Thanks

 

[Igcse stuff]

once you solve the past pprs from 2004-2012 then u can easily score 30-36 marks easily in that ....
P1 P2 P4 ...score max marks then u can easily get an A*

Thank you very much! .....by the what should I do to get full marks in P2 P3 P4 and P5

 

[Sadia Jahan Lisa]

Assalamualaikum.
How are you all? I need a help. I am a AS student. I will sit for AS examination in coming May-June. I need only the numerical values or practical reading for past practical question papers of chemistry & physics, so that I can do the further tasks of those practical question papers. Can anyone help me please?

 

[Sadia Jahan Lisa]

I need a help. Is there anyone who can help me?

 

[ZaqZainab]

I need a help. Is there anyone who can help me?

Help with?

 

[Sadia Jahan Lisa]

I am a AS student. I need the experimental reading of past year question paper for chemistry practical so that I can do the further calculations. Can anyone help? Please please please

 

[Abdel Moniem]

River water in a chalky agricultural area may contain Ca2+, Mg2+, − 2
3
CO , −
3
HCO , Cl
− and −
3
NO
ions. In a waterworks, such water is treated by adding a calculated quantity of calcium hydroxide.
What will be precipitated following the addition of calcium hydroxide?
A CaCl2
B CaCO3
C Ca(NO3) 2
D Mg(NO3)2

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_13.pdf
question 16 and 17

 

[ahmed abdulla]

Assalamualaikum.
How are you all? I need a help. I am a AS student. I will sit for AS examination in coming May-June. I need only the numerical values or practical reading for past practical question papers of chemistry & physics, so that I can do the further tasks of those practical question papers. Can anyone help me please?

For chem its mostly .. c1v1 = c2v2 .. or c=n/v and mole= mass/mr .... Q=mCt
For phy v=Ir .. and rest will be said in the question

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_13.pdf
question 16 and 17

As it can be seen X- was oxidised to X2 so it worked as a reducing agent. x- reacted with two other oxidising agents, Y- did with nine and Z- reacted with only one. So X- is strongest and Y- is weakest.
For seventeen, it can be seen that the oxidation only occurs when sulphuric acid reacts with sodium iodide. In all other casses, the products have the same oxidation states. The acidic gas formed was HCl.
Iodine gas has zero state while iodide had -1. Purple color shows that iodine was released.
Therefore, it can be deduced that H2SO4 is stronger oxidising agent than iodine.

 

[Suchal Riaz]

I am a AS student. I need the experimental reading of past year question paper for chemistry practical so that I can do the further calculations. Can anyone help? Please please please

Do atp of o level. It has the reading and all u need to do is to draw graph or do working.

 

[MiniSacBall]

I finished my Chemistry in 20 DAYS..!!! still Getting about 30/60 (paper-2)
Getting WORRIED!

Same here! Chemistry AS is a nightmare!. I am trying to gain control over it. I have finished the course too, but Past Papers are worst night mare, i have ever had!

 

[Hassan Ali Abid]

Thank you very much! .....by the what should I do to get full marks in P2 P3 P4 and P5

Its not that difficult to score good marks in atleast P2 and P4 ...... For this you should be knowing each and everything thing of the syllabus on the fingre tips , concepts should be clear ...and then revising the stuff on regular intervals to ensure that u have retained all what u have prepared ...and then attempting past pprs (*the way u solve the ppr also counts a lot )and then finally discussing the things/doubts and all that with your teacher ...All these things will surely be contributing to get good marks and its very possible to get even full marks and in this way then u wont be having that much tension for either P3 or P5 and easily you can score A*.
P.s even if you get C's or D's in P3 or P5 and very high A grades in P1,2,4 even then you can get an overall A* .

 

[Hassan Ali Abid]

Same here! Chemistry AS is a nightmare!. I am trying to gain control over it. I have finished the course too, but Past Papers are worst night mare, i have ever had!

As chem is a piece of cake ...If u are getting low marks in the P2 ..thats just bcz you haven't prepared the course well ...once you are done with the course only then pick up the pprs and you'll see that getting 55+ is not a big task .

 

[scouserlfc]

Same here! Chemistry AS is a nightmare!. I am trying to gain control over it. I have finished the course too, but Past Papers are worst night mare, i have ever had!

Concentrate on what the person above said. Plus also dont make this assumption of chem being nightmare a reality just think about it as the easiest subject or whatever and try to motivate yourself when doing it because if you dont do it then you will never get over this chemistry nightmare thing and will continue to suffer and in the end u will give up all hope.
So get the syllabus and books and start going through the course again and try to understand whats going on instead of learning everything. Plus if u can do then try for all AS topics the MCQs of very old papers of 80s and 90s they are a wonderful source of building concepts but do the MCQs for each topic on syllabus after u read it. I did this all and then in last month before exam i did past papers and had no problem ALHUMDULILLAH. But im not here to boast but to share my experience so it helps you
By the way cheer up dont be sad as your smilie above shows