Biology; Chemistry; Physics: Post your doubts here!

[Amnaa]

It's exothermic.

How? :/

 

[farhan141]

Please explain http://papers.xtremepapers.com/CIE/...l O Level/Chemistry (5070)/5070_s11_qp_21.pdf

Q.B6(e)(ii) and B6(e)(iii).

 

[Saad Mughal]

How? :/

It's not part of our syllabus, this is calculated using bond energies, the energy involved in bond breaking is less than the energy involved in bond making.

 

[bubbles1997]

in graphite atoms are arranged in layers while in diamond are closely packed


in graphite each carbon atom is bonded to 3 other atoms while in diamond each is bonded to 4 other atoms

in diamond atoms are tetrahedrally arranged while in graphite are arranged in rings/hexagonal arrangement

graphite have some delocalised/mobile electrons while diamond dont have mobile electrons

diamond have strong covalent bonds between all the atoms while graphite contains weak forces between the layers

Thank you!

 

[bubbles1997]

Catalyst enhances both the back and forward reaction so equilibrium remains the same

oh, my bad...

 

[Amnaa]

can you give some examples on dissolving reaction?

 

[Saad Mughal]

Please explain http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s11_qp_21.pdf

Q.B6(e)(ii) and B6(e)(iii).

(ii) Mass increase at cathode = 1.44 - 1.20 = 0.24 g
Mass decrease at anode = 1.45 - 0.24 = 1.21 g

(iii) The current supplied by 80 A for 90 s = current supplied by 40 A for 180 s.
So decrease in mass at cathode = 0.24 g
Mass of cathode = 1.51 + 0.24 = 1.75 g

 

[Saad Mughal]

can you give some examples on dissolving reaction?

NaCl (s) ---> NaCl (aq.), Enthalpy change = +ve.

 

[farhan141]

Thanks!

 

[farhan141]

Same paper B7(b) and (d)(i)

 

[Snowysangel]

http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s03_qp_1.pdf
question no. 28 and 27

And Q12 of the same year

 

[Saad Mughal]

Same paper B7(b) and (d)(i)

(b) Just draw the basic alcohol structure of C4H9OH.
Saturated - Because it has carbon-carbon single bonds.

(d)(i) Acid (Ethanoic Acid) first then Alcohol (Ethanol).
The formula is CH3COOC2H5.

 

[Saad Mughal]

And Q12 of the same year

Use this formula,
Mass of Sulphur = % composition * 10 = Mass of sulphur/Molar mass * 10.
For (a) it is, 32/90 * 10 = 3.55 g
For (b) it is, 64/120 * 10 = 5.33 g
For (c) it is, 64/160 * 10 = 4 g
For (d) it is, 32/239 * 10 = 1.34 g
Answer is B.

 

[Snowysangel]

http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s05_qp_1.pdf
i've done this paper..
question no. 13, 18, 19, 22, 23, 33, 37 and 38 were wrong ! i got 32/40.. bad attempt :/

Is 24 b??

 

[Snowysangel]

Use this formula,
Mass of Sulphur = % composition * 10 = Mass of sulphur/Molar mass * 10.
For (a) it is, 32/90 * 10 = 3.55 g
For (b) it is, 64/120 * 10 = 5.33 g
For (c) it is, 64/160 * 10 = 4 g
For (d) it is, 32/239 * 10 = 1.34 g
Answer is B.

But that takes so much time. Isn't there a faster way to go about it?? Will the periodic table be given to us for paper 1 brw?

 

[Saad Mughal]

But that takes so much time. Isn't there a faster way to go about it?? Will the periodic table be given to us for paper 1 brw?

Yes, it's attached at the end.
Shorter method is to just get a rough estimate. I could tell that the mass in (b) was greater than in (c) and (d) by seeing the composition.
Only needed to calculate (a) to be sure.

 

[asma tareen]

http://papers.xtremepapers.com/CIE/...l O Level/Chemistry (5070)/5070_s12_qp_12.pdf
Q 31 anyone???

 

[Saad Mughal]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s12_qp_12.pdf
Q 31 anyone???

Daadi jaan. Aap bhi na!
Z displaces W.
W displaces X.
X displaces Y.
So, Reactivity is Z>W>X>Y.
Answer is C.

 

[Mohammad Farzanullah]

http://papers.xtremepapers.com/CIE/...l O Level/Chemistry (5070)/5070_w11_qp_12.pdf
i cant understand why is nitrogen the answer to Q1... plz help asap!

 

[asma tareen]

Daadi jaan. Aap bhi na!
Z displaces W.
W displaces X.
X displaces Y.
So, Reactivity is Z>W>X>Y.
Answer is C.

acha poutey jee