Chemistry: Post your doubts here!

[RoOkaYya G]

yeah its given in data booklet. ull get for Cl2 for Cl uve to divide the value by 2 normally

 

[Metanoia]

Thankyou, would you please explain Q13 of May June 05 and those of Nov 05 too?

Nov 05.
Qn3. The easiest way is first figure out the respective elements in the four options, then refer to the 2nd IEs in IE table in the data booklet.

A. Mg (compare its 2nd IE to Na and Al)
B. Al (compare its 2nd IE to Mg and Si)
C. Si (compare its 2nd IE to Al and P)
D. P (compare its 2nd IE to Si and S)



You can see that Al has a higher 2nd IE compared to its neighbours Mg and Si.

Qn 14. Again, use the data booklet.
"Element Y has the highest first ionisation energy " means that we can eliminate options B and C, leaving us with option A and D.
" Element Y has lowest melting point." means we can eliminate A (as sodium has a lower melting point than magnesium).
So we are left with D.
P has a lower melting point than Si (giant molecular structure) and S (stronger VDW forces)

A sodium, magnesium, aluminium
B magnesium, aluminium, silicon
C aluminium, silicon, phosphorus
D silicon, phosphorus, sulphur

May 05
Qn 13: Be and Al has similar electronegativity, this is the diagonal relation in the Periodic Table.
You can read a discussion on it in the paragraph "what is a diagonal relationship" in this link.
Other pairings are Li and Mg, B and Si.

 

[Anallia]

Can somebody please help me with Q1 (b) and Q2 (c) of the attached files? Incase of Q2 (c), how do we get to know the standard enthalpy change of atomisation of Chlorine? Where is it given in the data booklet?

use the bond energy for Cl-Cl bond given in the data booklet

 

[huh]

Can someone please help me with testing for gases during practical. How do we test for all the gases before all the gas has been liberated?

 

[Bilal Khan]

Can someone please help me with testing for gases during practical. How do we test for all the gases before all the gas has been liberated?

It's written in the last two pages of every practical , the identification of ions and gases . Ammonia turns moist red litmus blue .

 

[huh]

It's written in the last two pages of every practical , the identification of ions and gases . Ammonia turns moist red litmus blue .

Yes but whenever I do the test for gases, take burning splint and so on, all the gas liberates and I have mix the solutions again. Any way to prevent this? Thank you for replying.

 

[Bilal Khan]

Yes but whenever I do the test for gases, take burning splint and so on, all the gas liberates and I have mix the solutions again. Any way to prevent this? Thank you for replying.

That merely depends on your practice or handling skills . Take a larger volume so that more gas liberates or you can try bringing the test tube close to a lit bunsen burner.

 

[huh]

That merely depends on your practice or handling skills . Take a larger volume so that more gas liberates or you can try bringing the test tube close to a lit bunsen burner.

Ok. Thank you very much.

 

[Bilal Khan]

Ok. Thank you very much.

Anytime , my friend .

 

[RoOkaYya G]

Yes but whenever I do the test for gases, take burning splint and so on, all the gas liberates and I have mix the solutions again. Any way to prevent this? Thank you for replying.

jst block the mouth of the test tube with ur thumb until u light a splint. the gas wont escape.
n yeah try make larger volume of solutions...itll yield more gas.

 

[MYLORD]

Who is giving chemistry p-33 tomorrow ?

 

[RoOkaYya G]

Who is giving chemistry p-33 tomorrow ?

me .-.

 

[Thought blocker]

Alright. Incase of Nitrogen, the N-N bond energy is given as 944 in the data booklet. But in the marking scheme it is taken as 994. Which one is correct?

This is not possible. Which paper is like this?

 

[Metanoia]

Alright. Incase of Nitrogen, the N-N bond energy is given as 944 in the data booklet. But in the marking scheme it is taken as 994. Which one is correct?

The values might be different due to the different editions of data booklets.

 

[Thought blocker]

The values might be different due to the different editions of data booklets.

Why does it differ? :/

 

[Metanoia]

Why does it differ? :/

I can't say for sure why it differs in this specific case.

I were to guess, it could be that recent experiments and calculations done in the labs gave a more updated value.

 

[Thought blocker]

I can't say for sure why it differs in this specific case.

I were to guess, it could be that recent experiments and calculations done in the labs gave a more updated value.

As per my thinking, its her reading mistake. That's it.
Let's see.

 

[Thought blocker]

I can't say for sure why it differs in this specific case.

I were to guess, it could be that recent experiments and calculations done in the labs gave a more updated value.

As per my thinking, its her reading mistake. That's it.
Let's see.

Recent booklet 2014 : http://www.cie.org.uk/images/95996-2014-syllabus.pdf Same value, no change seen N=N bond energy remains 944 kJ/mol.

 

[Metanoia]

As per my thinking, its her reading mistake. That's it.
Let's see.

It really depends on the years, last time it was 994. For example, qn 19 of 2003.

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w03_qp_1.pdf

It became 944 in the more recent years.

 

[Thought blocker]

It really depends on the years, last time it was 994. For example, qn 19 of 2003.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_1.pdf

It became 944 in the more recent years.

For now, it remains same.
Thanks for the effort.