CHEM AND BIO HELP AND TIPS HERE

[Shazizzzle]

http://www.freeexampapers.us/IGCSE/Chemistry/CIE/2009%20Nov/0620_w09_qp_6.pdf
its q 4 e ii and iii
and q 5 d ii

e(i) Greater Temp. Change (BECAUSE it was in POWDER form, thus increasing the surface area, and so therefore faster reaction, producing a greater final temperature in the same time. Kimo has a point there. BUT this one is confirmed from the mark scheme)
e(ii)Half the temp change i.e 7.5 deg. C (as vol of acid is double)

5 d(ii) White precipitate which dissolves in excess (because this is NaOH. L is NaOH.)

[rhea]

why does an increase in volume lead to a decrease in temperature change?

[guMnam]

e(i) Greater Temp. Change (BECAUSE it was in POWDER form, thus increasing the surface area, and so therefore faster reaction, producing a greater final temperature in the same time. Kimo has a point there. BUT this one is confirmed from the mark scheme)
e(ii)Half the temp change i.e 7.5 deg. C (as vol of acid is double)

5 d(ii) White precipitate which dissolves in excess (because this is NaOH. L is NaOH.)

i didnt get e ii

[da_rockstar]

in biology do we find the uncertainty the same way that we do in physics?? for example for practicals they sometimes ask for uncertainty. so should i give it as (+-least count)?

P.S sahi baat hai itna mat khapo questions par...lol.

[Shazizzzle]

why does an increase in volume lead to a decrease in temperature change?

Because,
Imagine you've got the same Mg and 20 cm3 of acid.
Now, if you take the same amount of Mg, but DOUBLE the acid, 40 cm3,
There is MORE acid than before.
So, a greater volume of acid with which the Mg needs to react, i.e double, so half the temp. change.

The TOTAL temp change is brought about by the COMPLETE reaction.
If the acid volume is doubled, that means the quantity of Mg needed is halved as well.
If the vol is doubled, the quantity of Mg ALSO has to be doubled to get the same temp change.

Greater volume, more time to react with all of it. So, only half the job done, thus only half the temp change.

[SNA]

Hello.............
can sumone help me in chem??

im always confused when to use "warm" the solution or "heat" the solution.
i tot it did not matter.apparently it does.
how do you know which one to use?

thanks!!

[Shazizzzle]

ana ma3afi ma3loom.

[guMnam]

Hello.............
can sumone help me in chem??

im always confused when to use "warm" the solution or "heat" the solution.
i tot it did not matter.apparently it does.
how do you know which one to use?

thanks!!

see it totally depends on the q and wat is the eperiment abt.....for example if u aretesting for nitrate u dont heat u warm it...bla bla just remember tht heating is a faster increase in temp ...and rest if u have brains u can distinguish and ans well....

[Baladya]

Because,
Imagine you've got the same Mg and 20 cm3 of acid.
Now, if you take the same amount of Mg, but DOUBLE the acid, 40 cm3,
There is MORE acid than before.
So, a greater volume of acid with which the Mg needs to react, i.e double, so half the temp. change.

The TOTAL temp change is brought about by the COMPLETE reaction.
If the acid volume is doubled, that means the quantity of Mg needed is halved as well.
If the vol is doubled, the quantity of Mg ALSO has to be doubled to get the same temp change.

Greater volume, more time to react with all of it. So, only half the job done, thus only half the temp change.

What about the speed?

[SNA]

see it totally depends on the q and wat is the eperiment abt.....for example if u aretesting for nitrate u dont heat u warm it...bla bla just remember tht heating is a faster increase in temp ...and rest if u have brains u can distinguish and ans well....

i c...
thanks!!!!:D
but it still means i need to either memorize or understand wat im doing though.
sigh...but thanks!
 

[guMnam]

Because,
Imagine you've got the same Mg and 20 cm3 of acid.
Now, if you take the same amount of Mg, but DOUBLE the acid, 40 cm3,
There is MORE acid than before.
So, a greater volume of acid with which the Mg needs to react, i.e double, so half the temp. change.

The TOTAL temp change is brought about by the COMPLETE reaction.
If the acid volume is doubled, that means the quantity of Mg needed is halved as well.
If the vol is doubled, the quantity of Mg ALSO has to be doubled to get the same temp change.

Greater volume, more time to react with all of it. So, only half the job done, thus only half the temp change.

just one small doubt.igot most of u....but still if the acid has doubled...it means tht 20cm3 of it is in excess and the rest of the reaction is still the same nuthin has mainly changed it is just tht there is less water and more glases to be filled.y would the rate or ane thnid change..the glasses are extra

[guMnam]

i have noticed tht all pprs have the q 5 on test for cations and anions....it is so weired.:S

[Vin]

paper 5 and 6 is all about them ..

[DEGO]

p6 chm nov2000 3 D
pls some one xplain it to me plsss and the answer

[WARRIOR]

p6 chm nov2000 3 D
pls some one xplain it to me plsss and the answer

remember whn i said less soluble and more solube?

crystas would appear at lower temp becaz they dissolve at lower temp