Chemistry study thread (2 Viewers)

[kazan]

depends how they combine, their is a differnce between decomposition and other reactions so it would react differntly with each type

my question

balance these equations and name all reactants and products

Na(s) + Cl2(g) -> NaCl(s)

CaCO3(s) + HNO3(aq) -> Ca(NO3)2(aq) + CO2(g) + H20(l)

NaHCO3(s) -> CaCO3(s) + H2O(l)

 

[felixcthecat]

balance these equations and name all reactants and products

2Na(s) + Cl2(g) -> 2NaCl(s)
sodium + chloride -> sodium chloride

CaCO3(s) + 2HNO3(aq) -> Ca(NO3)2(aq) + CO2(g) + H20(l)
calcium carbonate + hydrogen nitrate -> calcium nitrate + carbon dioxide + water


and this one... how do u do it?? is it possible =.='' firstly Na became Ca after the reaction sumhow O_0 and.. yea.. just doesn't seem to work..
NaHCO3(s) -> CaCO3(s) + H2O(l)

question: a bit of a repeat of my previous but maybe a bit more clear~ do we need to remember the electronegativity of major elements such as carbon.. oxygen..hydrogen..?

 

[Loz_metalhead]

and this one... how do u do it?? is it possible =.='' firstly Na became Ca after the reaction sumhow O_0 and.. yea.. just doesn't seem to work..
NaHCO3(s) -> CaCO3(s) + H2O(l)

That does seem right. The sodium has to be in the product doesnt it?

 

[Loz_metalhead]

Ok heres another fact. metal reactivity.

metal + oxygen-----> metal oxide

Active metal + water----->metal hydroxide + hydrogen gas

Active metal + dilute acid-----> salt + hydrogen gas

Acid+ carbonate----> salt + carbon dioxide + water

Less Active metal + water----> Metal oxide+ hydrogen gas

Active metal oxide + Water---->metal hydroxide.


Yeh you should know these. Lol.

 

[felixcthecat]

yupyup~~ wuts *active metal* tho?

 

[mitsui]

like umm... potassium, sodium, magasium..etc. etc.

=]

i catn remember all that equations, so i will juz go with my instinct... =O=..usual wrong tho

 

[Loz_metalhead]

ok activity increases from right to left of the periodic table. My teacher didnt explain it very well. But obviously metals in group one are very active....also group 2.

 

[felixcthecat]

oh yea! i remember now.. like how reactive they are.. yupyup =P

 

[YBK]

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=

Thanks!!!!!

for ur question, if product becomes a metaloxide doesn't that make it heavier or something...?

 

[mitsui]

nah the whole thing is heavier coz of oxygen...hmmm..i reckon it is gonna remain the same
oh well, finger crossed, hope there is no that Q in my test. =P

 

[insert-username]

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

The mass will be greater because oxygen molecules from the air have combined with the metal. The Law of Conservation of Mass states that the mass of the reactants is equal to the mass of the products, and this is still true - the oxygen is a reactant.


question: a bit of a repeat of my previous but maybe a bit more clear~ do we need to remember the electronegativity of major elements such as carbon.. oxygen..hydrogen..?

You won't need to remember specific electronegativities, but you will have to know what electronegativity is and what its trends are, i.e. electronegativity increases going up and right the Periodic Table.


I_F

 

[mitsui]

ohh so when they talk about "samples of metals" we include the oxygen too? xD??
i thot it is juz the mass of the metal... thx =P

 

[YBK]

Yay! I was right

 

[YBK]

compare mass change in samples of metals when they combine with oxygen.

They said sample of metals, but that sample has reacted with oxygen. So in order to weigh the new reacted sample, we have to also weigh the oxygen with it.

metal + oxygen = metal oxide

we measure the metal oxide, which is the mass of metal + oxygen

Hope that makes more sense now.

 

[kazan]

NaHCO3(s) -> CaCO3(s) + H2O(l)

i made a typo in that one

it should be 2 differnt equations


NaHCO3(s) -> Na2C03 + CO2(g) + H2O(l)


Ca(OH)2(aq) + CO2(g) -> CaCo3(s) + H2O(l)

sorry bout that i got them off a sheet and a wrote them into the computer wrong. my bad

 

[mitsui]

ok i will answer
the sample of metal will increase in mass due to the mass of the oxygen in its oxided form. =P
bingo

 

[HamuTarou]

WooT!!! my exams ar over!!! chem today!

any more questions?

 

[mitsui]

i don realli haf Qs but .. XD.. i cant remember anything in specific~~~
how did u test go? Oo

 

[kazan]

upon analysis a hydrocarbon was found to contain 82.6% carbon and17.4% hydrogen.
(a) Calculate its empirical formula.
(b) Could this be an alkane? if so suggest molecular formula

 

[mitsui]

a] so let the hydrocarbon be 100g
then mass of C is 82.6g
mass of H is 17.4g

then n(C)=7..
n(H)=17.4

mole ratio: C:H is 1:2.5
so empirical formula is C2H5

so no, i dont it is an alkane.. XD..but mite be wrong, wat u do think?