Chemistry: Post your doubts here!

[Ahmed Aqdam]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s03_qp_1.pdf
Question 8

Remember: Oxygen always has oxidation state -2 and hydrogen +1 (except metal hydrides e.g.NaH). Every uncombined element has zero oxidation number

A: Nitrogen has +3 oxidation number in NH3 which reduces to -2 in NO. The change is 5.
B: Oxidation number of nitrogen is +4 in NO2 and +5 in HNO3 as in the NO3- ion Oxygen has total of -6 so the ion has -1. The change is 1.
C: +2 in NO and +4 in NO2. Change is 2.
D: -3 in NH3 and +2 in NO.Zero in N2. Biggest change is 3.

Hence the greatest change is in A (5).

 

[KWIKIW]

6 Three compounds have the physical properties shown in the table.

compound P Q R
melting point / °C 2852 993 –119
boiling point / °C 3600 1695 39
conductivity (solid) poor poor poor
conductivity (liquid) good good poor
conductivity (aqueous) insoluble good insoluble


What might be the identities of P, Q and R?

P Q R
A MgO KCl NH3
B MgO NaF C2H5Br
C SiO2 KCl C2H5Br
D SiO2 NaF HCl


35 When a firework is lit, a fuel and an oxidising agent react together.

In one such firework, magnesium is the fuel and barium nitrate is the oxidising agent.

Which solids are produced when the firework is lit?
1 BaO
2 MgO
3 Mg(NO3)2

What are the correct statements?


36 In a car engine, non-metallic element X forms a pollutant oxide Y.

Further oxidation of Y to Z occurs spontaneously in the atmosphere. In this further oxidation,
1 mol of Y reacts with 0.5 mol of gaseous oxygen.

Which statements about X, Y and Z are correct?
1 The oxidation number of X increases by 2 from Y to Z.
2 The molecule of Y has no unpaired electrons.
3 The molecule of Z contains three oxygen atoms.

What are the correct statements?

 

[KWIKIW]

This is the complete question.

 

[A star]

Any one here for chem and/or p5 inbox me or just tag me here ill inbox you we can prep togetherand help each other(over xpf) cause i guess the old ones who used to help arent active anymore :/

 

[sara kamal]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w06_qp_4.pdf

please explain Q2 c(3)
will be very thankful !

 

[Browny]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_12.pdf

Can anyone please explain Q35, Q36?

 

[yousef]

Paper5- mj2009
q 1(e) ..& if someone can even do second question graph and share it with us that will be much appreciated.

 

[M Haseeb Javed]

How do you find pH of a buffer solution?

 

[ritesh isuri]

help me plz with this: A solutiion A is saturated with both calcium hydroxide and calsium sulphate. both are sparingly soluble. a)pH of A is 12.3 find concentration of OH-.
b) Ksp of calsium hydroxide =4.0*10^-5, find concentration of calcium ions in A
c)Ksp of calcium sulphhate is 2.5*10^-5, find conc of sulphate ions in A.

 

[halloffame]

well thanks for ur help but I only need from chapter 17-30 and in pdf format

In the CD ROM folder Go to the following folder and select the pdf belonging to there respective chapters :

CHEMISTRY _ AS & A CD ROM\AS and A Level Chemistry CB\source_data\Answers_questions

 

[halloffame]

well thanks for ur help but I only need from chapter 17-30 and in pdf format

Here is the .ZIP file containing the answers from chap 17 to 13. Hope it will help u. .>>>>>> Hit LIKE

PASSWORD : chem

 

[danial 234]

can any1 answer this???
are HCl, HBr, HI strong acids in aqueous solutions??

 

[danial 234]

6 Three compounds have the physical properties shown in the table.

compound P Q R
melting point / °C 2852 993 –119
boiling point / °C 3600 1695 39
conductivity (solid) poor poor poor
conductivity (liquid) good good poor
conductivity (aqueous) insoluble good insoluble


What might be the identities of P, Q and R?

P Q R
A MgO KCl NH3
B MgO NaF C2H5Br
C SiO2 KCl C2H5Br
D SiO2 NaF HCl


35 When a firework is lit, a fuel and an oxidising agent react together.

In one such firework, magnesium is the fuel and barium nitrate is the oxidising agent.

Which solids are produced when the firework is lit?
1 BaO
2 MgO
3 Mg(NO3)2

What are the correct statements?


36 In a car engine, non-metallic element X forms a pollutant oxide Y.

Further oxidation of Y to Z occurs spontaneously in the atmosphere. In this further oxidation,
1 mol of Y reacts with 0.5 mol of gaseous oxygen.

Which statements about X, Y and Z are correct?
1 The oxidation number of X increases by 2 from Y to Z.
2 The molecule of Y has no unpaired electrons.
3 The molecule of Z contains three oxygen atoms.

What are the correct statements?

6) ans is B
cz R is liquid at rtp and according to choices.. bromoethane is liq so ans must be C or B..... and as P conducts electricity in liq state so it must be ionic that is Mgo..
so ans is B

35) in fireworks reactions, metal oxides are produced not metal nitrate so ans becomes B 1 &2

36) it says that further oxidation occurs spontaneously so X must be N, Y be NO...and Z be NO2.....
1 is correct cz in NO, N has ox state +2 and in NO2 it has +4
2 is wrong cz there are unpaired electron in molecule of No
3 is wrong cz NO2 has 2 oxygen atoms

 

[sidbloom1995]

i have a doubt in october november 2010 p41 question 4 part c iii n iv
can anyone answer it?

 

[sidbloom1995]

can any1 answer this???
are HCl, HBr, HI strong acids in aqueous solutions??

HCl is a strong acid because it can be fully ionized
HBr and HI can also be fully ionized but compare to HCl they are weaker!!

 

[sidbloom1995]

I have a question > When we want to use Bond energy of Cl2 >> as its quoted in the
Data booklet it should be 242 .. but for Many time i have seen that they are using 244 as the answer !
Why? which data should we quote if the question came to us ?
one of the questions is o'n 2009 va' 41

TheZodiac
6Astarstudent

yes i came across that myself
just make sure that ur method is correct
the mark scheme is wrongly printed
i checked the previous data booklets and they also have 242
as long as ur procedure was correct u dont have to worry about the mark scheme using 244 instead of 242

 

[yousef]

yes i came across that myself
just make sure that ur method is correct
the mark scheme is wrongly printed
i checked the previous data booklets and they also have 242
as long as ur procedure was correct u dont have to worry about the mark scheme using 244 instead of 242

No bro , every year the values change !
so you get new data booklet every year , and make sure you use the value in the booklet you are given on the day of exam

 

[Browny]

Danial thanks for the help.
But in 36) why can't it be SO to SO3 and CO to CO2.
and in 35), is MgO insoluble.

 

[danial 234]

Danial thanks for the help.
But in 36) why can't it be SO to SO3 and CO to CO2.
and in 35), is MgO insoluble.

in 36) it cant be SO to SO3 and CO to CO2. cz these reactions dont occur spontaneously. in air...
in 35) MgO is very slightly soluble.

 

[williamcwz]

The cracking of a single hydrocarbon molecule, CnH2n+2, produces two hydrocarbon molecules only. Each hydrocarbon product contains the same number of carbon atoms in one molecule. Each hydrocarbon product has non-cyclic structural isomers.
What is the value of n?
A 4 B 6 C 8 D 9