Chemistry: Post your doubts here!

[ad98ify]

can anyone answer it? please? A2 students?

View attachment 5963

anyone???

 

[trgirl]

can u answer this question plss ??
explain why enthalpy change of formation of water is identical to the standard enthalpy change of combustion of hydrogen.

 

[smzimran]

can u answer this question plss ??
explain why enthalpy change of formation of water is identical to the standard enthalpy change of combustion of hydrogen.

H2(g) + 0.5O2(g) --> H2O(l)
Same equation for both thats why

 

[Muhammad Bin Anis]

Have a look At the question and explain it to me

View attachment 5821 Please someone explain it
marking scheme says D
and i chose"B"

any one please explain this to me

 

[tom ed]

http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_s09_qp_32.pdf

Question number 2 ..part g)....how are we supposed to select a suitable mass for FB5 and how can the tmperature error be kept to a minimum..

 

[saudha]

do part b somebody!!plssssssss

 

[hassam]

why buckminsterfullerene has lower m.p than graphite

 

[Amy Bloom]

why buckminsterfullerene has lower m.p than graphite

Because the intermolecular forces in there are van der waal's forces.

 

[Amy Bloom]

View attachment 6078

do part b somebody!!plssssssss

Well i've just come across this question quickly but i've not done the calculations, yet this is my point of view:
Carbon dioxide will be absorbed by the sodium hydroxide pellets. So, the total volume of gas will be that of N2 and O2 only. Proceed as in (a) without taking carbon dioxide into consideration. What do you think?

 

[saudha]

Well i've just come across this question quickly but i've not done the calculations, yet this is my point of view:
Carbon dioxide will be absorbed by the sodium hydroxide pellets. So, the total volume of gas will be that of N2 and O2 only. Proceed as in (a) without taking carbon dioxide into consideration. What do you think?

i think thts right ...............thxxx

 

[kimkimyap]

HELP!!
In a car engine, non-metallic element X forms a pollutant oxide Y.
Further oxidation of Y to Z occurs in the atmosphere. In this further oxidation, 1 mol of Y reacts
with ½ mol of gaseous oxygen.
What can X be?
1 carbon
2 nitrogen
3 sulfur

answer is 2 and 3. can anyone pls explain why carbon is not one of the answer?


And this
Hydroxyapatite, Ca5(PO4)3OH, is the main constituent of tooth enamel. In the presence of saliva,
the following equilibria exist.
Ca5(PO4)3OH(s) 5Ca2+(aq) + 3PO (aq) + OH–(aq)
HPO (aq) H+(aq) + PO (aq)
Which of the following statements help to explain why tooth enamel is dissolved more readily
when saliva is acidic?
1 The hydroxide ions are neutralised by the acid.
2 The phosphate ion PO (aq) accepts H+(aq)
3 Calcium ions react with acids.

answer is 1 and 2. why 3 is not one of the answer?

 

[smzimran]

HELP!!
In a car engine, non-metallic element X forms a pollutant oxide Y.
Further oxidation of Y to Z occurs in the atmosphere. In this further oxidation, 1 mol of Y reacts
with ½ mol of gaseous oxygen.
What can X be?
1 carbon
2 nitrogen
3 sulfur

answer is 2 and 3. can anyone pls explain why carbon is not one of the answer?


And this
Hydroxyapatite, Ca5(PO4)3OH, is the main constituent of tooth enamel. In the presence of saliva,
the following equilibria exist.
Ca5(PO4)3OH(s) 5Ca2+(aq) + 3PO (aq) + OH–(aq)
HPO (aq) H+(aq) + PO (aq)
Which of the following statements help to explain why tooth enamel is dissolved more readily
when saliva is acidic?
1 The hydroxide ions are neutralised by the acid.
2 The phosphate ion PO (aq) accepts H+(aq)
3 Calcium ions react with acids.

answer is 1 and 2. why 3 is not one of the answer?

Probably because CArbon is not there in the car engine

Calcium ion cannot accept any protons so how will it react with acid?

 

[umarashraf]

HELP!!
In a car engine, non-metallic element X forms a pollutant oxide Y.
Further oxidation of Y to Z occurs in the atmosphere. In this further oxidation, 1 mol of Y reacts
with ½ mol of gaseous oxygen.
What can X be?
1 carbon
2 nitrogen
3 sulfur

answer is 2 and 3. can anyone pls explain why carbon is not one of the answer?


And this
Hydroxyapatite, Ca5(PO4)3OH, is the main constituent of tooth enamel. In the presence of saliva,
the following equilibria exist.
Ca5(PO4)3OH(s) 5Ca2+(aq) + 3PO (aq) + OH–(aq)
HPO (aq) H+(aq) + PO (aq)
Which of the following statements help to explain why tooth enamel is dissolved more readily
when saliva is acidic?
1 The hydroxide ions are neutralised by the acid.
2 The phosphate ion PO (aq) accepts H+(aq)
3 Calcium ions react with acids.

answer is 1 and 2. why 3 is not one of the answer?

in carbon monooxide, oxidation state of the whole compound is +4-2 = +2... and CO2 has oxidation state of +4-4=0... so CO2 is formed by reduction not oxidation....

 

[johnsth]

hey guys can you give me chemsistry AS and A2 notes which are according the syllabus

 

[kimkimyap]

Probably because CArbon is not there in the car engine

Calcium ion cannot accept any protons so how will it react with acid?

in carbon monooxide, oxidation state of the whole compound is +4-2 = +2... and CO2 has oxidation state of +4-4=0... so CO2 is formed by reduction not oxidation....

Thanks a lot u guys..!!

 

[umarashraf]

Thanks a lot u guys..!!

welcome sir... hey in fact i thought CO2 was formed by oxidation ... i just discovered the answer today after your post..

 

[smzimran]

Thanks a lot u guys..!!

welcome sir... hey in fact i thought CO2 was formed by oxidation ... i just discovered the answer today after your post..

Hello, u r wrong there,
In CO, the oxidation state of carbon is +2 and NOT +4 so the whole compound is uncharged (+2 -2 = 0),
If It was charged we would have refered to it as carbon monooxide ion but we do not!

If u are in A2, you should know that Group IV elements have two oxidation states (+2 and +4)

Conclusion:
CO2 is formed by oxidation as one Oxygen atom is added and 'Addition of oxygen is OXIDATION'

Dont confuse yourselves people !

 

[Mustehssun Iqbal]

Assalamu alaikum,
How to identify dependent and independent variables in P5??

 

[steel]

Where can i get the answer ?
the chemistry application booklet answer

 

[XPFMember]

hey guys can you give me chemsistry AS and A2 notes which are according the syllabus

www.chemguide.co.uk
contains notes classified according to our syllabus.