Chemistry: Post your doubts here!

[salvatore]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_21.pdf
No. 5 d (ii)

Please help understand how to solve the question above.. I'm completely blank!
An explanation will be appreciated..
Thanks

 

[scouserlfc]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_21.pdf
No. 5 d (ii)

Please help understand how to solve the question above.. I'm completely blank!
An explanation will be appreciated..
Thanks

Basically u should be aware of Hess law which is in chemical energetics chapter to do this so make sure u remember it ! If not then check your book because its a big thing to explain and this is isnt the only type of way a Hess law question can come u can have diffferent ways of getting answers like using bond energies,enthalpy of neutralisation ..................................

 

[raamish]

can anyone explain how does oxygen come in the part 3c of j11/42 chemistry paper 4??

 

[magnesium]

IS F-F BOND STRONGEST OR WEAKEST???????????
HELP PLZ WID DETAILED ANS!

 

[iKhaled]

can anyone explain how does oxygen come in the part 3c of j11/42 chemistry paper 4??

SO4 2- NO3 - F- Cl- OH- Br- I-

everythin before OH- stays and O2 is given off and everything after OH- is given off instead of OH-

 

[scouserlfc]

IS F-F BOND STRONGEST OR WEAKEST???????????
HELP PLZ WID DETAILED ANS!

It depends on how you are comparing it with other bonds because its a bond in which both atoms are same so the bond polarity case is ruled out and it should be more weak as its just like those normal bonds ! But i wouldnt go deep in this as im pretty sure that the bond strength is not only directly proportional to bond polarity and inversly proportional to the bond length but it is also related to other factors so just remember this ! And it would be appreciated and would help to explain if u can give us a particular question in which this is used! if u just want to see the bond energy then just check the syllabus (go to the end part in the Data Booklet and u will find a page in which they give details of specific bonds that are to be tested probably in enthalpy change questions )

 

[magnesium]

It depends on how you are comparing it with other bonds because its a bond in which both atoms are same so the bond polarity case is ruled out and it should be more weak as its just like those normal bonds ! But i wouldnt go deep in this as im pretty sure that the bond strength is not only directly proportional to bond polarity and inversly proportional to the bond length but it is also related to other factors so just remember this ! And it would be appreciated and would help to explain if u can give us a particular question in which this is used! if u just want to see the bond energy then just check the syllabus (go to the end part in the Data Booklet and u will find a page in which they give details of specific bonds that are to be tested probably in enthalpy change questions )

In the upper atmosphere chlorofluoroalkanes (CFCs) are broken down to give chlorine radicals
but not fluorine radicals.
What is the best explanation for this?
A Fluorine is more electronegative than chlorine.
B Fluorine radicals are less stable than chlorine radicals.
C The C–F bond is stronger than the C–Cl bond.
D The chlorine atom is larger than the fluorine atom

 

[magnesium]

It depends on how you are comparing it with other bonds because its a bond in which both atoms are same so the bond polarity case is ruled out and it should be more weak as its just like those normal bonds ! But i wouldnt go deep in this as im pretty sure that the bond strength is not only directly proportional to bond polarity and inversly proportional to the bond length but it is also related to other factors so just remember this ! And it would be appreciated and would help to explain if u can give us a particular question in which this is used! if u just want to see the bond energy then just check the syllabus (go to the end part in the Data Booklet and u will find a page in which they give details of specific bonds that are to be tested probably in enthalpy change questions )

https://thol.sunway.edu.my/examdbase/alv/chem/p1/chem_p1_n06.pdf
Q38.....

 

[scouserlfc]

https://thol.sunway.edu.my/examdbase/alv/chem/p1/chem_p1_n06.pdf
Q38.....

In this one all three options are correct the reactivity of halogenoalkanes increases more as u go down the grp 7 ! then they are absolutely non flammable bromodichloroflouromethane was used as flame retardants so definitely flourine wont budge too then C-F bond is the most strongest halo- carbon bond check the bond energies of these halogenoalkanes

In the upper atmosphere chlorofluoroalkanes (CFCs) are broken down to give chlorine radicals
but not fluorine radicals.
What is the best explanation for this?
A Fluorine is more electronegative than chlorine.
B Fluorine radicals are less stable than chlorine radicals.
C The C–F bond is stronger than the C–Cl bond.
D The chlorine atom is larger than the fluorine atom

The simple definition is that the C-F bond is the strongest halo-Carbon bond so you require more energy than the UV light can provide to break it

 

[salvatore]

Basically u should be aware of Hess law which is in chemical energetics chapter to do this so make sure u remember it ! If not then check your book because its a big thing to explain and this is isnt the only type of way a Hess law question can come u can have diffferent ways of getting answers like using bond energies,enthalpy of neutralisation ..................................

Thanks.. I kinda get it

 

[unseen95]

Hello and AsSalamoAlaikum,
I have a problem in 9701/01/M/J/04 question numbers 1 and 3. How do we solve these questions? Anyone please help with step by step procedure.

 

[scouserlfc]

Hello and AsSalamoAlaikum,
I have a problem in 9701/01/M/J/04 question numbers 1 and 3. How do we solve these questions? Anyone please help with step by step procedure.

First of all for 1 find the mole of ATOMS of hydrogen that is 1/1 =1 now just check in the same way any of the given gases give the same moles as this you dont really need to multiply 6.02*10^23 because u dont know the exact answer so neon is the answer and its C !

for 3 find the moles of sodium azide first (50/51) and then divide by 2 because you have two moles of this azide now using ratios find the moles of Nitrogen by multiplying by 3 and then find the volume by multiplying by 24 which gives you 27.7 dm^3 which is C

 

[unseen95]

First of all for 1 find the mole of ATOMS of hydrogen that is 1/1 =1 now just check in the same way any of the given gases give the same moles as this you dont really need to multiply 6.02*10^23 because u dont know the exact answer so neon is the answer and its C !

for 3 find the moles of sodium azide first (50/51) and then divide by 2 because you have two moles of this azide now using ratios find the moles of Nitrogen by multiplying by 3 and then find the volume by multiplying by 24 which gives you 27.7 dm^3 which is C

Thanks for your help. Wish to get similar helps in the future too.

 

[unseen95]

Question: Which substance, in 1 mol dm-3 aqueous solution, would have the same hydrogen ion concentration as 1 mol dm-3 of hydrochloric acid?
Answer is nitric acid. How is this the answer? Please help.

 

[SulmanAli]

any resource for the preparation for p3 !

 

[scouserlfc]

Question: Which substance, in 1 mol dm-3 aqueous solution, would have the same hydrogen ion concentration as 1 mol dm-3 of hydrochloric acid?
Answer is nitric acid. How is this the answer? Please help.

Basically first find the conc. of H+ ion in HCl which is 1/1 = 1 mol/dm^3 (try concentrating on the moles of H+ ions it is 1 too )

Now just find an acid in which u have same moles of acid in 1 mol/dm^3 of acid which is HNO3 u can also have other acids but this is a common one so u should give this as the answer !

any resource for the preparation for p3 !

For P3 you might want to learn or get the hang of the different ppt tests and be assured of which test is for which ion so that you save time during exam ! Also go through all papers and see parts where u had difficulty (you must have done them in the first place before !!! ) ! Otherwise there isnt much to revise because this is abt how u do the practical things efficiently !

 

[code11]

An aqueous solution contains 1 mol of S2O3^-2 ions and this reduces 4 mol of Cl2 molecules. What is the sulphur containing product of this reaction?
A. S
B. SO2
C. SO3^-2
D. SO4^-2

is this question right? if yes whats the answer ?

 

[unseen95]

I will be very thankful for help. I have a problem in question number 3(c)(iii) calculation part of 9701/02/M/J/04. I could not understand the marking scheme. Somebody please help me with a step by step procedure.

 

[PhyZac]

Asslamu Alikum Wa Rahmatullah Wa Barakatoho... scouserlfc


2 Use of the Data Booklet is relevant to this question.....(9701/1/O/N/03)
A garden fertiliser is said to have a phosphorus content of 30.0% ‘P2O5 soluble in water’.
What is the percentage by mass of phosphorus in the fertiliser?
A 6.55%
B 13.1 %
C 26.2%
D 30.0%

Why is the Answer B ?

5 The table gives the successive ionisation energies for an element X.
............................................1st... 2nd.... 3rd ....4th...... 5th.... .6th
ionisation energy / kJ mol–1.... 950. 1800 .2700.. 4800 ....6000...12300
What could be the formula of the chloride of X?
A XCl
B XCl2
C XCl3
D XCl4

Why is the answer C?

 

[scouserlfc]

Asslamu Alikum Wa Rahmatullah Wa Barakatoho... scouserlfc


2 Use of the Data Booklet is relevant to this question.....(9701/1/O/N/03)
A garden fertiliser is said to have a phosphorus content of 30.0% ‘P2O5 soluble in water’.
What is the percentage by mass of phosphorus in the fertiliser?
A 6.55%
B 13.1 %
C 26.2%
D 30.0%

Why is the Answer B ?

5 The table gives the successive ionisation energies for an element X.
............................................1st... 2nd.... 3rd ....4th...... 5th.... .6th
ionisation energy / kJ mol–1.... 950. 1800 .2700.. 4800 ....6000...12300
What could be the formula of the chloride of X?
A XCl
B XCl2
C XCl3
D XCl4

Why is the answer C?

Wallaikum As Salam !
Its quite simple actually !
it tells u first that the fertilizer has 30% P2O5 content so it means actually u have 100g of fertilizer of which 30g is P2O5
so just find the mass of phosphorus content using simple ratio ,
142(Mr of P2O5) ----- 30
62 ------ x
x=13.1%

there is a big jump in iE values from 3 to 4 abt 2000 KJ but this isnt really enuf to tell us that the new shell starts here probably it shows the start of s subshell so now u can be assured that its from grp 5 now remember how hydrogen bonds with nitrogen and requires exactly 1 electron like Cl atoms and has a formula NH3 so Cl will have NCl3 (the use of atoms here is just for an example its not necessary its the real one )

I will be very thankful for help. I have a problem in question number 3(c)(iii) calculation part of 9701/02/M/J/04. I could not understand the marking scheme. Somebody please help me with a step by step procedure.

Use first the part i answer for 3c which is 0.05 now use the ratio of the equation as acid is in a ratio of 1:2 with the ammonia half the moles of the ammonia and u have the moles of H2SO4 which is 0.025 now use the conc. of H2SO4 and the moles to get the volume of H2SO4 in dm^3 and convert it into cm^3 by multiplying with 1000 .