Author Topic: CHEM AND BIO HELP AND TIPS HERE  (Read 357064 times)

6394

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2580 on: June 05, 2010, 01:21:24 pm »
m/j 2005
chem ppr 3
q4 d   
how do u noe x=2
Thanks

Offline sarasa

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2581 on: June 05, 2010, 01:24:09 pm »
umm... i already know this ,see i was kinda wondering why this happens... sorry
I think i can explain y but on one condition my doubt gets answered about da labelled diagram, ok?
U know dat any reversible reaction at da state of equilibrium means dat neither sides is prevailing so if it goes in one direction, it undergoes da reverse reaction so it continues to go like this until u change da conditions which could be increasing da pressure as da first example, so think of a piston being pushed, what happens to volume of air, it decreases, rite? so this is da exact same thing on increasing pressure, volume decreases so da side of da rection with lower volume (remember this only for gas) would be favoured, u can know that by looking at da no. of moles...
NOW, da second example is increasing da concentration, if u add more of A in this reaction, wat would happen? A+B=>C+D
There is more of A nd this disturbs da equilibrium in order to return to it, the reaction speeds up towards the RHS in order to remove da extra A added
LAST is temperature, usually either da forward or da backward would be exothermic(gives off heat) nd naturally da other would be endo (takes in heat)
so when u raise da temp., equilibrium is again disturbed so to decrease it da endo is favoured why because it takes in heat so will eventually lower da temp. Got it???

Offline JD46

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2582 on: June 05, 2010, 01:25:34 pm »
MJ04  Q4 how do i know  what salt to use, what cant it be a zinc oxide or hydroxide for preparing an insolubles salt?
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Offline $H00t!N& $t@r

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2583 on: June 05, 2010, 01:25:45 pm »
no not that way
it ws sumthin like
above 'this' metle
only elctrolysis
and so on so forth

cud u tell me bout that
like explain
plz?
Method of Extraction
The method used depends on the reactivity of the metal

Very reactive metals

Electrolysis (Decomposing metal compound with electricity)
Potassium
Sodium
Calcium
Magnesium
Aluminium

Moderately reactive metals

Heating metal oxide with coke
Zinc
Iron
Lead

Low Reactivity metals
Heating metal compounds in air
Copper
Silver
"If A equals success, then the formula is:
A=X+Y+Z, X is work. Y is play. Z is keep your mouth shut"- Albert Einstein

Offline rameeziiii

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2584 on: June 05, 2010, 01:27:46 pm »
m/j 2005
chem ppr 3
q4 d   
how do u noe x=2
Thanks
looking it up

Offline sarasa

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2585 on: June 05, 2010, 01:29:44 pm »

Offline sarasa

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2586 on: June 05, 2010, 01:30:42 pm »
or maybe this.... idk if its correct
Thanks

Offline rameeziiii

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2587 on: June 05, 2010, 01:34:07 pm »
looking it up
ok...umm...well... OK!...
79.1g of CaSO4 is 79.1/136 moles of CaSO4 (i.e. 0.58 moles)
20.9g of H2O is 20.9/18 moles water (ie. 1.16 moles)
now divide by the simplest mole ratio (0.58) to obtain X

Offline $H00t!N& $t@r

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2588 on: June 05, 2010, 01:34:41 pm »
m/j 2005
chem ppr 3
q4 d   
how do u noe x=2
Thanks

mol=mass/MM    so for CaSO4 : mol=79.1/136 = 0.58mol    and for H2O: mol=20.9/18= 1.16mol
To find x you have to find the mole ratio
so divide each of them with the smallest one
therefore in this case 0.58mol is smaller than 1.16 so    0.58/0.58=1  and x=   1.16/0.58=2   therefore x=2
"If A equals success, then the formula is:
A=X+Y+Z, X is work. Y is play. Z is keep your mouth shut"- Albert Einstein

Offline $H00t!N& $t@r

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2589 on: June 05, 2010, 01:35:48 pm »
ok...umm...well... OK!...
79.1g of CaSO4 is 79.1/136 moles of CaSO4 (i.e. 0.58 moles)
20.9g of H2O is 20.9/18 moles water (ie. 1.16 moles)
now divide by the simplest mole ratio (0.58) to obtain X

oops didnt see you already replied  :P
"If A equals success, then the formula is:
A=X+Y+Z, X is work. Y is play. Z is keep your mouth shut"- Albert Einstein

Offline $H00t!N& $t@r

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2590 on: June 05, 2010, 01:37:59 pm »
sorry i have another question...
 s09 q9c  
If it has already been answered then can u please give me the link

can anyone pls ans my question...  :'(
"If A equals success, then the formula is:
A=X+Y+Z, X is work. Y is play. Z is keep your mouth shut"- Albert Einstein

Offline JD46

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2591 on: June 05, 2010, 01:38:20 pm »
MJ04  Q4 how do i know  what salt to use, what cant it be a zinc oxide or hydroxide for preparing an insolubles salt?

I'D LIKE A REPLY! theres been like 3 replies AFTER my post ,but no rresonse to my post! ???
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http://igcseprep.blogspot.in/

Offline rameeziiii

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2592 on: June 05, 2010, 01:39:10 pm »
MJ04  Q4 how do i know  what salt to use, what cant it be a zinc oxide or hydroxide for preparing an insolubles salt?
i dont know that one but i think sodium oxide or hydroxide would destroy the carbonate or something although carbonates are alkaline

6394

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2593 on: June 05, 2010, 01:39:46 pm »
thnxu both
:)

Offline rameeziiii

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2594 on: June 05, 2010, 01:41:25 pm »
can anyone pls ans my question...  :'(
working....