Chemistry: Post your doubts here!

[xxfarhaxx]

can some1 help me from these, please:
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_11.pdf
Q11, Q13,Q23,Q29

11. ass: A- cu2+ ions remain unchanged at the end of the reaction..c reactions 2 n 3..

13- C - SiCl4 + 2H2O----> SiO(s) +HCl(acidic)

 

[user]

Assalamoalaikum wr wb!

need help, plz... ...

P.S. I'm reposting them

 

[mominzahid]

Be isn't really a typical group 2 element. Like I said before, Be2+ is smaller and has a higher charge density than the other group 2 elements and its charge density is similar to that of Al's. The rest of the group 2 elements are bigger than Al and don't really have a high charge density.

Let me try to give a better explanation:

Al is a small atom with a 3+ charge. All of these group 2 elements have a 2+ charge. For the atoms to have the same electronegativity, you would want the atom to be smaller to make the net effect the same. Be is the only atom which is smaller, so the effect of charge density on both Al and Be is similar.

Thank you so much that helped.

 

[KurayamiKimmi]

Q2) Write down all of the data you have.

Mr = 14x + 16y
Mass = 0.23 g
Moles = 0.23 / (14x + 16y) - (1)
Moles = 0.005 (since they said it occupies 120 cm^3) - (2)

Equate (1) with (2):

0.07x + 0.08y = 0.23
7x + 8y = 23

And then try each option and see if they add up to 23. In B, 7(1) + 8(2) = 23 so it's right.

There's probably a few other methods of solving this question, but this one worked for me.

12) NaCl is completely ionic, SiCl4 is completely covalent. AlCl3 has a lot of covalent character and isn't that much ionic and MgCl2 is the opposite of that. Since they asked which one shows just some covalent character, MgCl2 should be right.

16) "The enthalpy of formation of HCl and HI is represented by the equations:


H2 + Cl2 --> 2HCl

and

H2 + I2 --> 2HI

The enthalpy change of these reactions can be found by looking at the bonds broken and formed in terms of their energies (remembering that bond breaking is endothermic and bond formation is exothermic):

ΔH(rxn) = ΔH(reactant bonds) - ΔH(product bonds)

So if the HI bond energy is much smaller than the HCl bond energy (option C) then the HI reaction will be more endothermic...

... whereas if the bond energy of I2 were smaller than the bond energy of Cl2 (option D) the reaction forming HI would be more exothermic.

And as we know that the reaction forming HI is more endothermic, the correct answer is C"

18) "A solid nitrate fertiliser reacts with an alkali to produce a gas which turns damp pH paper blue."

Read the bolded parts. The anion must be nitrate and the cation must be NH4+.

So you have NH4NO3 whose empirical formula is N2H4O3.

26) For it to be chiral, the central C atom MUST be bonded to 4 different groups. One of them will be OH, the minium the rest will have to be is:

- CH3
- CH3CH2
- CH3CH2CH2

In total, that's 6 + the central C atom which is 7.

36)
1 is right, the more down you go group 7, the more readily dissociation occurs.
2 this only happens with Flourine I think.
3 is wrong because only the halide ions are good reducing agents.

Thank you so much !!! ^_^

 

[ultraviolet]

Oct/Nov 2010 Q: 3, 7, 9 and 10 please :|
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf

SOMEONE HELP ME!!!!!!!!!!!

 

[7amed]

A household bleach contains sodium chlorate(I), NaClO, as its active ingredient. The
concentration of NaClO in the bleach can be determined by reacting a known amount with
aqueous hydrogen peroxide, H2O2.
NaClO(aq) + H2O2(aq) → NaCl(aq) + O2(g) + H2O(l)
When 25.0 cm3 of bleach is treated with an excess of aqueous H2O2, 0.0350mol of oxygen gas is
given off.
What is the concentration of NaClO in the bleach?
A 8.75 × 10

moldm

0.700moldm

C 0.875moldm

D 1.40moldm'
ANSWER IS D
Anyone please

 

[samwickz]

are you sure its C ? and your question is right ?

ya deffa
http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_s06_qp_1.pdf
Q no 10

my ans is A wbt u?

but d marking scheme ans IS C

 

[saudha]

Use of the Data Booklet is relevant to this question.
Which element is likely to have an electronegativity similar to that of aluminium?
A barium
B beryllium
C magnesium
D strontium


why is it B....how?

 

[saudha]

Concentrated sulfuric acid can behave both as a strong acid and as an oxidising agent.
With which compound does concentrated sulfuric acid react in this way?
A ethanol
B magnesium carbonate
C propanenitrile
D sodium bromide
why D why not A???

 

[saudha]

The products obtained by cracking an alkane, X, are methane, ethene and propene.
The mole fraction of ethene in the products is 0.5.
What is the identity of X?
A C6H14 B C8H18 C C9H20 D C11H24
how do u get the answer?

 

[saudha]

How many isomers with the formula C5H10 have structures that involve π bonding?
A 3 B 4 C 5 D 6
this too is confusing!!

 

[saudha]

is Alkenes and Arenes ... nucleophillic or electrophillic?

 

[saudha]

how do u do Q 29 and 30?/

 

[saudha]

2 When a sample of a gas is compressed at constant temperature from 1500 kPa to 6000 kPa, its
volume changes from 76.0cm3 to 20.5cm3
Which statements are possible explanations for this behaviour?
1 The gas behaves non-ideally.
2 The gas partially liquefies.
3 Gas is adsorbed on to the vessel walls

why is 1 only correct...?it might be liquified as well??? so 2 should also be correct ..why isnt it???

 

[umarashraf]

2 When a sample of a gas is compressed at constant temperature from 1500 kPa to 6000 kPa, its
volume changes from 76.0cm3 to 20.5cm3
Which statements are possible explanations for this behaviour?
1 The gas behaves non-ideally.
2 The gas partially liquefies.
3 Gas is adsorbed on to the vessel walls

why is 1 only correct...?it might be liquified as well??? so 2 should also be correct ..why isnt it???

compressing at constant temp will never liquify any gas... you have to cool the cylinder as well for liquifying... else the cylinder will blast away....

 

[saudha]

compressing at constant temp will never liquify any gas... you have to cool the cylinder as well for liquifying... else the cylinder will blast away....

ohh right...dint think abt tht... WoW thxx ...

 

[umarashraf]

ohh right...dint think abt tht... WoW thxx ...

u welcome..

 

[umarashraf]

is Alkenes and Arenes ... nucleophillic or electrophillic?

alkenes are nothing.. but arenes have a ring of pie electrons which behaves as strong strong nuclophile....

 

[umarashraf]

The products obtained by cracking an alkane, X, are methane, ethene and propene.
The mole fraction of ethene in the products is 0.5.
What is the identity of X?
A C6H14 B C8H18 C C9H20 D C11H24
how do u get the answer?

is the answer B...?? if yes then i think i can explain u easily..if not then... ... ...

 

[saudha]

is the answer B...?? if yes then i think i can explain u easily..if not then... ... ...

YES THE ANS IS B