All chemistry Doubts here :)

[JmCullen]

I have a doubt
1.http://www.xtremepapers.me/CIE/Cambridg ... _qp_12.pdf
Question (14)
I think chlorine will go to anode (yellow green) and hydrogen at cathode (colourless) because it is concentrated NaCl but the answer is something else
2.http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_1.pdf
Question 15

THANKS

1) Since they are talking about the universal indicator, the chloride will be colourless.. what you're talking about (yellow green) is the gas. and universal indicator is the liquid inside the tube. so, in the anode, will be colourless (because chloride present.) and cathode will be purple/blue. (because OH- is present)

2) i don't really sure too. haha.. sorry..

 

[xIshtar]

There would be a temperature decrease of 20C, as the reaction is endothermic, and there is a smaller volume of solvent.

 

[xIshtar]

Guys I was wondering what did you do for the last question in paper 6 variant 1, where it says what happens when the cleaning liquid is added to a sink containing a fizzy drink?
I wrote that fizzy drinks contain carbonic acid which will react with the cleaner and release/liberate chlorine which is a toxic gas [as it was mentioned in the question]. But some of my friends have been saying that will explode and other stuff like that....anyone got a confirmed answer?

What I wrote too

 

[HyDraZin3]

y only temperature decrease and not increase? and can u explain me the whole question step by step? :sorry:

 

[Yoyo1994]

Hi all, would it be required for us to know the boiling points for alkanes, alkenes and alcohols up to but/pent?

 

[OrlandoBloom<3]

I dont think its necessary for you to to know the boiling points of alkanes alkenes and all that you have mentioned

 

[TheCookieMonster]

Hey everyone, so could someone plz help me out, i was doing nov.08 v2 p3 and i don't get some stuff.
Here's a link to the paper, go to Variant 2:
http://www.xtremepapers.me/CIE/Cambridg ... _qp_03.pdf

Here's a link to the mark scheme, again go to variant 2:
http://www.xtremepapers.me/CIE/Cambridg ... 8_ms_3.pdf

Q4a.iii) I wrote sodium nitrate and sodium chloride. in the mark scheme it says sodium carbonate/oxide/hydrogencarbonate. Why?

Q4b.ii) I don't get the answer in the mark scheme. I wrote 12:1 :S ??

Q7a.i) I don't get how to do this one at all could someone please explain?!

 

[xIshtar]

Hey everyone, so could someone plz help me out, i was doing nov.08 v2 p3 and i don't get some stuff.
Here's a link to the paper, go to Variant 2:
http://www.xtremepapers.me/CIE/Cambridg ... _qp_03.pdf

Here's a link to the mark scheme, again go to variant 2:
http://www.xtremepapers.me/CIE/Cambridg ... 8_ms_3.pdf

Q4a.iii) I wrote sodium nitrate and sodium chloride. in the mark scheme it says sodium carbonate/oxide/hydrogencarbonate. Why?

Q4b.ii) I don't get the answer in the mark scheme. I wrote 12:1 :S ??

Q7a.i) I don't get how to do this one at all could someone please explain?!

Heh, I don't see much of an explanation why oxide and carbonate are needed rather than chloride or nitrate.. In all honesty, carbonate and oxide are the first things that come to me first..

92.3/ Rmm of Carbon = 7.7 (1dp).. 7.7:7.7 = 1:1.

This one is pretty simple..

Mole Ratio = 1:6.5 => 65cm^3 out of the 100cm^3 is used.. This implies that 35cm^3 is left..

Now considering the mole ratio in comparison to Carbon Dioxide.. 1:4 => 40cm^3 is formed.

 

[HyDraZin3]

xishtar answer my question plz

 

[xIshtar]

y only temperature decrease and not increase? and can u explain me the whole question step by step? :sorry:

The temperature decreases as the reaction is endothermic
You know that 1000cm^3 produces a 10C reduction, so half the volume will produce double the temperature change as it is less saturated..

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I have seen many people ask about Question 5.b)

So, I thought I would explain it to everyone here

From the graph, 8cm^3 of the Phosphate reacts fully with 12cm^3 of T Nitrate.

So, identifying only the atoms we need:

T : Phosphate
8 : 12
3T : 2 Phosphate
24 : 24.

This implies that the formula is T3(PO4)2

If anyone has any other questions, I'll do my best

 

[HyDraZin3]

http://www.xtremepapers.me/CIE/Cambridg ... 4_qp_3.pdf
Question 4(b) (ii) and (iii)

Plz help me

 

[xIshtar]

http://www.xtremepapers.me/CIE/Cambridge%20IGCSE/0620%20-%20Chemistry/0620_s04_qp_3.pdf
Question 4(b) (ii) and (iii)

Plz help me

Hmm, I'm stumpted with 4(b) (ii)

But I can do 4.(b)(iii) : Look at the chemicals used, aluminium and sodium hydroxide. So, as the amount used increase into excess, the precipitate will dissolve, meaning that it will go up, then steeply back down again.

I'll have another look for (ii) too.

 

[xIshtar]

Ahhh! I think I get it.. Iron (iii) is 3+, and Iron (ii) is 2+, and thus, Only 2/3 of the volume would be used, so it would level off at 8cm^3 of Sodium Hydroxide, but still producing the same height ppt.

 

[xIshtar]

And according to the mark scheme, what I said is right

 

[HyDraZin3]

http://www.xtremepapers.me/CIE/Cambridg ... 4_qp_3.pdf
Question 6 (b) (i)
In this question i know that its a ester linkage and also i know that OH goes from acid and H from alcohol at both ends, but i think there is a extra O in the starting which is written in the mark scheme

Hydroxide will not dissolve in excess with iron chloride?

Xishtar, i am really sorry if i am disturbing u by asking questions :sorry:

 

[xIshtar]

-OOC-C6-H4-CO-O-CH2-CH2-O-

I personally put the Hs on the end, but I'm not sure if it's correct to, as you have to show continuation..

 

[HyDraZin3]

See what i think is, if H and OH will go from both sides, the polymer should be :- -OC-C6H4-COOCH2CH2-0-
My polymer is correct, but in the mark scheme they are adding one more O in the start :- -OOC-C6H4-COOCH2CH2-0- and i dont understand why there is this addition :unknown:

 

[JmCullen]

hey. can anyone help?

Water is added to a test-tube containing dilute sulphuric acid of pH 4.
What could be the pH of the resulting solution?

 

[zkapoor]

Closer to, but less than 7. 5 or 6

 

[JmCullen]

it's 6. but can i know why?