Chemistry study thread (2 Viewers)

[HamuTarou]

yeah, water is polar. hard to explain y without an aid of a diagram. -.-' wat numbers ar u talkin about? electronegativity?

 

[mitsui]

there r numbers in chemistry?! ...aRGH!..XD
...
water is polar because it got two polar bonds between H and O... and it is not symmetrical
there r polar bonds becoz both H ends r slightly positive charged (delta +)..and oxygen end is slightly negatively charged (2delta -)...

and polar basically means the unequal sharing of electrons.. frankly, oxygen gets more electron than hydrogen..

blah. xD

 

[pLuvia]

the electronegativity is the electron attracting power of the atom within a bond, you don't need to know it but just how the range of electronegativity affects the either it is a polar, non polar or ionic bond~

 

[HamuTarou]

no numbers in chem...unless the avogadro's number...

pretty good explaination! cant do better...

 

[mitsui]

lolz. thx!! *bows*

that is a confidence boost for my thrusday test..xD

 

[pLuvia]

i think you need to know the SLC and STP plus as HamuTarou said avogadro's number
SLP - standard lab conditons
STP - standard temperature and pressure

STP - T (*C) - P (KPa) - Vm (L/mol)
0 101.3 22.41
SLC - 25 101.3 24.47

Formulae

n - number of moles
V = Volume in litres (L)
Vm = molar volume

n = V / Vm

i think that's all you need to know about the number's right?? the atomic mass is given to you on the periodic table so you can work out the molecular weight of things

 

[HamuTarou]

my school gives u the STP, SLC info behind the periodic table in the paper, u just have to work out which one to use. eg:experiment peformed at 25C (lab condition)

the number changes, cus my says 24.79 at SLC, just stick to the one in ur exam paper.

funny thing is this wasnt covered in the textbook (chem context 1)...teacher had to go over it during our revision.

 

[pLuvia]

yeh same.. that book didnt say anything about it.. teacher had to teach ur it ><"

 

[mitsui]

my Q b4 the test.! >.<!
dot point (water) 3.2
analyse the relationship between the solubility of substances in water and the polar nature of the water molecules

...do we juz say... "..it is polar, sso it dissolves polar stuff.... and it got hyrdrogen bonding, strong enough to break a lot of ..other intermolecular forces?...and it reacts wif some ionic compunds and break the lattice up??"..


thx

 

[HamuTarou]

well it depends on the substance. it has to polar and how polar it is. lets say ethanol..it dissolves in water because of the plar end from the OH, the CHs are ignored. once u get a long chain of CHs and only one OH at the end, the OH becomes to weak compare to the long chains (C40), it will not dissolve in water. so u have soluble, slightly soluble and insoluble

the hydrogen bondings are between the molecules, it doesnt break other intermolecular forces. these forces determine their physical properties (mp & bp)

u answered the second part of the dot point already

 

[mitsui]

hmm i hate the dot pts, they r so confusing..
like... teachers told us about the pollutions to the water cycle (plastic, acid..blah bah)
but it is not on the syllabus..
do i have to study for thursday?!..

 

[pLuvia]

well if the teacher said about it.. it would most likely be in the test.. a little extra knowledge won't hurt anyone since it is a school exam.. it would most prob be in the test.. what ever you learn actually

 

[mitsui]

grrr.. studying is not my hobbie... =|..
oh well.. i will cram..

like the word "explain" the meaning of specific heat capacity
.. wat u explain about?..
wat is the cause? effect? the relationship.. XD

 

[pLuvia]

lol.. what the hell is specific heat capacity.. ive heard of it ><"

 

[mitsui]

u srs? i think our whole yearly is gonna be base on that crap
it is juz the heat energy required to change the temperature of 1g of a substance by 1Kelvin

....i think i spelt the last word rite... X___X

 

[pLuvia]

lol.. that should be right.. the word kelvin that is

 

[mitsui]

err then the whole sentence is correct, i am looking at that page in "chem context 1" rite now,, juz not consuming anything inside my brain.. XD

 

[HamuTarou]

ok...u have the formula:

/\H = mC/\T

/\: delta (change in..i know its dodgy, suppose to be a triangle)
H: energy in joules
m: mass of the substance being cooled or heat in grams
C: specify heat capacity (joules/grams kelvin)
T: temperature (final - initial)

the heat capacity is like the amount of heat it can absorb. water is consider to have a high heat capacity (4.18). one reason we can live on earth because of the high heat capacity, absorbing all the heat for the sun.

do u guys know how to use the formula?

 

[YBK]

• perform a first-hand investigation, analyse information and use available evidence to model the differences in atomic arrangement of diamond, graphite and fullerenes

Does anyone know of any real world applications to this dot point?

Arggg..... supposed to be "skills"

 

[mitsui]

diamond

graphite

fullerene

real world application???

diamond - jewellery - sparkles when polished and cut
glass cutting and polishing, mineral exploration drills, dentist's drills
record player needles

graphite - electrode in dry cells, dry lubricant, mixed with cly to make "lead" pencil, as it is soft and layered and slippery, conduct electricity

no usage of fullerenes r asked so i cbb to rmemeber it.. xD...


hope it helps xD

my Q! - compare mass change in samples of metals when they combine with oxygen."

i dont get it... xD..r the masses going to be the same before and afta reaction? coz law of consveration of matter,,, =O=