Chemistry doubts..ask here!

[shan5674]

ur welcm

what i understand from u is u want what happen to the substance when impurity is added ???

then when impurity is added it decrease the melting point of the substance and increase the boiling point of the substance
it is alwayz (RULE)

to identify if water is pure
boil it and it will eveporate exactly at 100'C if it is pure

hope im right

Yup thank you

Coz i came across a question where they gave us a table stating boiling points and melting points of substances and wanted us to state which substances are liquid, solid, gas etc at room temperature and im not really sure how to tell. This question usually comes up in paper 3 yeah? but just in case could you explain

 

[haochen]

i dont understand ur question
can u eleborate??

it is better for u to post the paper and tell me which question

but in general is and substance hv melting below 25 it is liquid at rtp

 

[shan5674]

i dont understand ur question
can u eleborate??

it is better for u to post the paper and tell me which question

but in general is and substance hv melting below 25 it is liquid at rtp

http://www.xtremepapers.me/CIE/Cambridg ... 6_qp_3.pdf

question 2

 

[Unkownbunny]

hey guys im so sorry but ive got loads of questions hope you guys don't mind to answer? cheers in advance

http://www.xtremepapers.me/CIE/Cambridg ... _qp_62.pdf (3 d) (4 g)
and whats the solvent in chromotography :S? read it in the marking scheme i got really confused xx

http://www.xtremepapers.me/CIE/Cambridg ... 9_qp_6.pdf (2 c)

http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf (4 F)

http://www.xtremepapers.me/CIE/Cambridg ... 7_qp_6.pdf (4 c)


and also, whats the difference with sulfate and carbonate? i thought i undersstood until i read the marking scheme, confused me :S
the meaning decant?


Thanks xx

 

[haochen]

i dont understand ur question
can u eleborate??

it is better for u to post the paper and tell me which question

but in general is and substance hv melting below 25 it is liquid at rtp

http://www.xtremepapers.me/CIE/Cambridg ... 6_qp_3.pdf

question 2

the first answer is A B and D
because their m.p.is above 25

RULE:
m.p. above 25 solid
m.p. below 25 liquid
b.p. above 25 liquid
b.p. below 25 gas
ONLY AT RTP

try doing the others by urself to see if understood

 

[zaisha54]

i need a proper defination for decant?

 

[shan5674]

i need a proper defination for decant?

To pour out the liquid from an insoluble solid/liquid mixture and leaving the solid behind.

hope this helps

 

[zaisha54]

thnks tht really helped

 

[haochen]

hey guys im so sorry but ive got loads of questions hope you guys don't mind to answer? cheers in advance

http://www.xtremepapers.me/CIE/Cambridg ... _qp_62.pdf (3 d) (4 g)
and whats the solvent in chromotography :S? read it in the marking scheme i got really confused xx

http://www.xtremepapers.me/CIE/Cambridg ... 9_qp_6.pdf (2 c)

http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf (4 F)

http://www.xtremepapers.me/CIE/Cambridg ... 7_qp_6.pdf (4 c)


and also, whats the difference with sulfate and carbonate? i thought i undersstood until i read the marking scheme, confused me :S
the meaning decant?
Thanks xx

first answer:
for the first one it will be steeper be cause more surface are
for the second one it will return to room temp or u can write the initial temp from the table

second answer:
exothermis because neutralization give out heat
and u cant write neutralization b/coz it is given

third answer:
find hw much they use at first and hw much they use now and do cross multiplication

forth answer:
read the reading from the graph and then do the cross multiplication
or u can see if it is doubled so do the same with it

Sulphate and carbonate u can differentiate them by the anion test.

decanting is the pouring of a liquid to seperate the liquid and solid

hope u got it

 

[lavanyamane]

hey guys im so sorry but ive got loads of questions hope you guys don't mind to answer? cheers in advance

http://www.xtremepapers.me/CIE/Cambridg ... _qp_62.pdf (3 d) (4 g)
and whats the solvent in chromotography :S? read it in the marking scheme i got really confused xx

http://www.xtremepapers.me/CIE/Cambridg ... 9_qp_6.pdf (2 c)

http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf (4 F)

http://www.xtremepapers.me/CIE/Cambridg ... 7_qp_6.pdf (4 c)


and also, whats the difference with sulfate and carbonate? i thought i undersstood until i read the marking scheme, confused me :S
the meaning decant?


Thanks xx

1. <3d> The lumps are smaller, so the reaction will be faster and hence the graph will be steeper/ drawn above the original. But it will level off at the same point as the first one because only the surface area has changed, not the concentration.
<4g> The mixture would be at room temperature/ initial temperature because the reaction is complete and there will be no more temperature changes.
Solvent is just the liquid you place your chromatography paper in, which dissolves the spot to dissociate it. (water/organic solvent are the solvents)
2. <2c> It is an exothermic reaction. You get the hint for this from the question when it says "polystyrene cup" (obvio to reduce heat loss) and "measure max temp reached". This shoes that a rise in temp is produced, showing it's exothermic, even if you don't know it before.
3. <4f> It would be double that required for 25 cm3, that is, the experiment in the question. This is because the volume of the solution has doubled, so the volume of potassium permangeanate must also double to neutralize the increased volume of solution B.
4. <4c> The same principle as the previous question applies here. The volume required would be half because in this case, the volume of solution B is getting halved (from 20 cm3 in the experiment to 10 cm3 in the question)

Hope I helped xx

 

[narutogirl]

quick question about what kokeeto said
22) how can you distinguish between hydrochloric acid and nitric acid? Add silver nitrate, in which white ppt will be formed with hydrochloric acid, but there will be no reaction with nitric acid.

can someone explain this

 

[Unkownbunny]

haochen and lavanyamane , Thank you sooo much i should really read the question more carefully xxxx
Thanks you sososoosos much xxxxx

 

[Mclovin]

quick question about what kokeeto said
22) how can you distinguish between hydrochloric acid and nitric acid? Add silver nitrate, in which white ppt will be formed with hydrochloric acid, but there will be no reaction with nitric acid.

can someone explain this

There is a chloride ion in the hydrochloric acid, Silver chloride is insoluble which forms a white precipitate
No chloride ion in nitric acid so no Precipitate

 

[lavanyamane]

haochen and lavanyamane , Thank you sooo much i should really read the question more carefully xxxx
Thanks you sososoosos much xxxxx

Any time

 

[narutogirl]

quick question about what kokeeto said
22) how can you distinguish between hydrochloric acid and nitric acid? Add silver nitrate, in which white ppt will be formed with hydrochloric acid, but there will be no reaction with nitric acid.

can someone explain this

There is a chloride ion in the hydrochloric acid, Silver chloride is insoluble which forms a white precipitate
No chloride ion in nitric acid so no Precipitate

okay maybe there is no precipitate but why is there no reaction with nitric acid?

 

[Mclovin]

quick question about what kokeeto said
22) how can you distinguish between hydrochloric acid and nitric acid? Add silver nitrate, in which white ppt will be formed with hydrochloric acid, but there will be no reaction with nitric acid.

can someone explain this

There is a chloride ion in the hydrochloric acid, Silver chloride is insoluble which forms a white precipitate
No chloride ion in nitric acid so no Precipitate

okay maybe there is no precipitate but why is there no reaction with nitric acid?

Because there is Nitrate ion in silver nitrate, so when it reacts with nitric acid it would still be silver nitrate as there is a nitrate ion also in nitric acid.

 

[lavanyamane]

http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_6.pdf
Q.2 (c) ?

 

[narutogirl]

ya i thought about that but i was like..but that couldn't be why..lol
thanks ^_^

 

[narutogirl]

http://www.xtremepapers.me/CIE/Cambridge%20IGCSE/0620%20-%20Chemistry/0620_w08_qp_6.pdf
Q.2 (c) ?

well because chlorine dissolves in water and it takes time for the undissolved excess chlorine to evolve

 

[haochen]

haochen and lavanyamane , Thank you sooo much i should really read the question more carefully xxxx
Thanks you sososoosos much xxxxx

ur welcm

quick question about what kokeeto said
22) how can you distinguish between hydrochloric acid and nitric acid? Add silver nitrate, in which white ppt will be formed with hydrochloric acid, but there will be no reaction with nitric acid.

can someone explain this

first of all u write down the formula HCL, HNO3 so H is the same so cancel out them
u will get CL and NO3 so it is up to u to choose the one u want to test for.
Kokeeto choose to test for CL so
add silver nitrate or lead nitrate to both of them
Cl is only present in the HCL so it will form white ppt. (anion test)
there is no N3 so no ppt. will be form in HNO3

hope u got them