IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: AN10 on September 12, 2009, 10:34:40 am
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white phosphorus reacts with dilute aq. solutions of copper (II) sulfate to deposit metallic copper and produce a strongly alkaline sol.
In an experiment to investigate this reaction, 0.31g of white phosphorus reacted in excess aq. copper sulfate giving 1.6g of metallic copper.
(i) Calculate the new oxidation number of the phosphorus after the reaction.
(ii) In the reaction, the phosphorus forms an acid HPOn, what is the value of n.
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(i) Ideally it should be +2...but i'm not very confident..think it's two cuz copper will accept two electron from phosphorous to become metal
(ii) H should also be having a subscrip...i've heard of nothing like this...plz check again
what is the answer though?
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i checked there is no subscript of H....n i dont know da answer....Thanks anywayz!...By the way do u hav any idea wht will be da equation for this reaction?
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nope the question is strange....i don't know how there's an alkaline solution being formed in the first place....I'll find out anyways
if the question is correct, then it's pretty unusual
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okay here you go...very strange reaction...
A Piece of ordinary phosphorus when placed in a solution of copper sulphate becomes covered with a black film of copper phosphide and then with a firm coating of bright metallic copper. The black phosphide is always found between the phosphorus and the copper.
check the pdf....i didn't get the head and tail of this reaction...a little new for me....
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guys i have a chem question .. i didnt want to open a new thread just for one question .. plz help !! :)
its about Molecular formula ..
Q. An organic compound containing only carbon, hydrogen and oxygen was found to have 62.07% carbon and 10.33% hydrogen.
What is its molecular formula if Mr= 58.0?
%s confuse me !! :(
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i am getting C6H12O2
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Thanks adi ..
can u guide me on how u did it plz ..
thanks !! :)
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Thanks adi ..
can u guide me on how u did it plz ..
thanks !! :)
.this how i did it...
C H O
MASS/100g 62.07 10.33 27.6
MOL. MASS 12 1 16
M/MM 5.1725 10.33 1.725
m/mm/1.725 3 6 1
emp. formula - C3H6O
Mr = 58
total mass of C + H + O = 58
58/58 = 1
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ooooh .. so its the same but we just remove the %s :P
Thanks a lot adi !! (u will do gr8 in ur nov exams and AS !! ;))
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ooooh .. so its the same but we just remove the %s :P
Thanks a lot adi !! (u will do gr8 in ur nov exams and AS !! ;))
arre..thanks man!....hope i do...!
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i thought C6H12O2 didnt exist
its butyl acetate ohh!!
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I guess the molecular formula remains as C3H6O.
This is the empirical formula with mass=58
Since molecular formula has mass 58, the empirical formula is the molecular formula.
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I guess the molecular formula remains as C3H6O.
This is the empirical formula with mass=58
Since molecular formula has mass 58, the empirical formula is the molecular formula.
ohh..yaah...true..
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By the way adi,
the EF is C3H6O
for the total mass, shouldnt we add up 3 carbons and 6 hydrogens etc. ? :-\
(is that what nid and u decided on just now? :P)
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By the way adi,
the EF is C3H6O
for the total mass, shouldnt we add up 3 carbons and 6 hydrogens etc. ? :-\
(is that what nid and u decided on just now? :P)
yah yah
my bad
tks nid
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yup that's what i did
12x3=36
+ 6x1=6
+16x1=16
Total=58
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Thanks guys !!
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anytime m8 :)
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hey guys, i have another question ..
Find the Empeical Formula of the following oxide of lead.
It contains 9.7g of lead to every 1g of oxygen
(RAM values .. Pb= 207, O= 16)
the answer is Pb3O4
i dunno what to do after we divide by the smallest answer =/
please help :)
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hey guys, i have another question ..
Find the Empeical Formula of the following oxide of lead.
It contains 9.7g of lead to every 1g of oxygen
(RAM values .. Pb= 207, O= 16)
the answer is Pb3O3
i dunno what to do after we divide by the smallest answer =/
please help :)
ok.somehow..i find this q wierd,.,
Pb O
9.7 1
207 16
0.04686 0.0625
1 1.33
u get it as PbO1.33 ===> PbO (app.)
is the mass of the oxide given...are the values correct?
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ya adi .. everything is correct ..
and nothing else is given .. ill have to talk to my teach tomorow cause thats what i got too ..
thanks for the help mate !! :)
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ya adi .. everything is correct ..
and nothing else is given .. ill have to talk to my teach tomorow cause thats what i got too ..
thanks for the help mate !! :)
maybe nid wud be able to solve this.,..
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maybe nid wud be able to solve this.,..
i sent her a pm .. maybe she can solve this chemical mystery :P
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I googled it
Single crystals of ?-PbO2 are formed when an intermediate oxide of lead represented by the generic formula, PbOx wherein x denotes a value falling in the range of 1.4 to 1.7, is heated in an aqueous alkali hydroxide solution under a pressure exerted by use of oxygen or an oxygen-containing gas. The single crystals are in the shape of slender rods, have a black color and have a metallic gloss.
and
he mechanochemical processes, including mechanochemical synthesis of mixed-valence lead oxides, in mixtures of PbO, Pb3O4, and PbO2were studied by x-ray diffraction. The results demonstrate that the reduction of Pb4+is accompanied by the formation of Pb2O3, Pb3O4, and possibly PbO1.37. Phases of variable composition close in structure to minium, Pb3O4, are shown to coexist during mechanical processing. The structure of the metastable oxide Pb3O4 – x with Pb2+: Pb4+> 2 (@O4 – 2x ) is tentatively determined. The sequence of the observed transformations is interpreted in terms of the model for the reaction zone, with consideration for primary and secondary interactions.
But I can't really figure it out..... confirm with your teacher
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ya i think i will ..
thanks for the help nid !! :)
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anytime q80
Actually I understood the formation thingy but I can't relate to the empirical formula :(
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anytime q80
Actually I understood the formation thingy but I can't relate to the empirical formula :(
i got a wierd answer
scroll up
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saw that...but that is related to the formation somehow....can't figure out how
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1-1.33
multiply by 3
3-4
formula is Pb3O4
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why would you multiply it by 3
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1-1.33
multiply by 3
3-4
formula is Pb3O4
i LOVE u !!!
thats what i wanted .. what do i multiply it by .. ur the man dude ..
thnxx alot !! ;D
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why would you multiply it by 3
to turn the decimal into a whole number ..
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why would you multiply it by 3
to make the ratio of lead to oxygen a whole number
since 1.33 is basically 4/3
so1*3:4/3*3=3:4
and q80boy.........no problem ;)
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hey guys, i have another question ..
Find the Empeical Formula of the following oxide of lead.
It contains 9.7g of lead to every 1g of oxygen
(RAM values .. Pb= 207, O= 16)
the answer is Pb3O4
i dunno what to do after we divide by the smallest answer =/
please help :)
u had ritten Pb3O3...wen asked if there was any change ..u said "no" the q was correct..
and y do v multiply only with 3 ......... u need to divide the mass of d substance wid 228.28 and then multiply it with PbO1.33
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to make the ratio a whole number......
1.33 isnt close enough to 1 to make it approximately equal to 1.........but if it were 1.03 i would have approximated it to 1
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to make the ratio a whole number......
1.33 isnt close enough to 1 to make it approximately equal to 1.........but if it were 1.03 i would have approximated it to 1
ohh..okk..
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Hey guys!
Here is a question I need help on:
i)-Oceanographers studying plankton found that a sample of seawater contained 1.20 nanomol dm^-3 of chlorophyll, C55H77MgN4O5. (1 nanomol= 1*10^-9 mol)
What mass of magnesium would be present in 1.00 cm^3 of this sample of seawater? Give your answer to three significant figures.
ii)- X-ray diffraction can be used to locate atoms or ions in molecules like chlorophyll. X-rays are scattered by the electrons in atoms and ions. In chlorophyll the atoms of one of the elements still cannot be located with certainty by this technique.
Suggest which element is most difficult to locate? (i think its hydrogen....not sure)
thanks in advance!
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ok here's the answer
no on moles= 1.2X10^-9 in one dm^3
therefore mass of Mg= 1.2X10^-9 X 24(mass of one mole)/ 1000( 1dm^3=1000cm^3)
=2.88X10^-11 g
check if it's right plz
and for the second one
I too think it's hydrogen because it has the least no of electrons in it's atom...which makes it difficult to locate it....diffraction is not enough to locate it
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ok here's the answer
no on moles= 1.2X10^-9 in one dm^3
therefore mass of Mg= 1.2X10^-9 X 24(mass of one mole)/ 1000( 1dm^3=1000cm^3)
=2.88X10^-11 g
check if it's right plz
and for the second one
I too think it's hydrogen because it has the least no of electrons in it's atom...which makes it difficult to locate it....diffraction is not enough to locate it
yup.. thats right,i got the same answerss
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yup.. thats right,i got the same answerss
Yippeeee!
yup they are right!
thanks guys!
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heyy guyz !!
my chem teacher is letting us live in hell! :P Moles and moles and more moles!
i need ur help in a couple of questions:
1. 0.0185 mol of hydrated MgSO4.xH2O has a mass of 4.56g. Calculate the number of molecules of water of crystallisation in the salt.
ur help is highly appreciated!! :D
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ok here u go
Mass og 1 mol of MgSO4=120g
mass of 0.0185mol=120X0.0185=2.22g
Mass of water=4.56-2.22=2.34g
1 mole of water=18g
there x moles= 2.34
no of moles of water in 0.0185 moles of hydrated magnesium sulphate=0.13
therefore no of moles of water=0.13/0.0185=7 moles
therefore MgSO4.7H2O
Cross check
Mass of 1 mole of MgSO4.7H2O=246g
4.56g= how many moles
cross multiply
gives 0.0185 moles
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thnxxxx :)
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heloooo .. its me again :P
i got a part of a question i need help with ..
in the following reaction ..
2NaOH + H2SO4 --> Na2SO4 + 2H2O
what would be observed if peices of red and blue litmus paper were added to Sodium sulfate after the reaction?
ur help is highly appreciated guyzz!! :D
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No change....cuz sodium sulphate is a salt...so it's neutral
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No change....cuz sodium sulphate is a salt...so it's neutral
thnxxxxx for ur help nid .. i really need to pay u back for ur chem knowledge :P
ur the best! ;)
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sodium sulfate is a salt therefore no change
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thnxxxxx for ur help nid .. i really need to pay u back for ur chem knowledge :P
ur the best! ;)
hehe Thanks q80
pay me back by getting good results :)......sounds familiar,huh? :P
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sodium sulfate is a salt therefore no change
Thanks adi :)
and nid lolz my mum hacked into ur account now? lolz :P
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u asked abt the colour change...
its important to use both the litmus papers...
if red litmus shows no change it means that it remains red which means its an acid
if blue litmus shows no change it means that it remains blue which means its an alkali
it cant be an acid and alkali together thus u can conclude that its a salt
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ahaaa .. i get it .. thanks adii!! ;)
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anytime dude...!!
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Hello guyss....here is what I need ur kind help again on : [c(ii)]
The main ore of lead is galena, lead(II) sulphide.
To produce lead, this ore is heated in air, when some of the lead(II) sulphide is converted to lead(II) oxide and sulphur dioxide.
The air supply is then cut off and on further heating the lead(II) oxide is converted, by reaction with the remaining lead(II) sulphide, to lead and sulphur dioxide.
Write an equation for (i) the conversion of galena to lead(II) oxide and (ii) the reaction of lead(II) oxide with lead(II) sulphide.
Answers:
(i) 2PbS + 3O2 ----> 2PbO + 2SO2
(ii) 2PbO + PbS ----> 3Pb + SO2
Qb) Calculate the total volume (m3) of sulphur dioxide which would be produced from 5.0 x 10^3 kg of galena in the reactions described in (a). (Assume that one mole of any gas occupies 2.4 x 10^-2 m3 at room temperature and pressure.) (3 marks.)
Answer: 1.004 m^3 ( not sure if its correct ; i did not convert the m^3 to cm^3, as the mass given is in kg...so i think its fine if we don't change the units..)
Qc)i) Another compound of lead, Z, which is found naturally contains 77.5% of lead and 4.5% of crbon by mass. The remainder being assumed to be oxygen. Calculate the empirical formula of the compound.
Answer: PbCO3 (not sure if its right.)
ii) 0.0500 mol of this compound Z gives, on heating, 11.2g of lead(II) oxide and a gas is evolved. What is the molecular formula of the compound Z?
idk how to solve this...
there are some more parts to this Q. i'll post la8er.
Thanks in advance..
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b) Combine the reactions
2PbS + 3O2 ----> 2PbO + 2SO2
2PbO + PbS ----> 3Pb + SO2
you get
3PbS+3O2--->3Pb+3SO2
ratio of sulphide to sulphur dioxide is 1:1
mass in 1 mole of lead sulphide=239.265
mass of lead sulphide used= 5x10^3 X1000g=5X10^6g
moles of lead sulphide=5x10^6/239.265
=20897.33moles
volume of sulphur dioxide=moles X 2.4X10^-2 =501.53 m3
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Pb C O
% 77.5 4.5 18
Mass 207.2 12 16
moles 77/207.2 4.5/12 18/16
=0.3716 =0.375 =1.125
ratio 1 1 3
empirical--PbCO3
you're right ;)
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Third one
molecular formula is CO2.....it's very obvious....
what confusion did u have in this one....easiest of the lot
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b) Combine the reactions
2PbS + 3O2 ----> 2PbO + 2SO2
2PbO + PbS ----> 3Pb + SO2
you get
3PbS+3O2--->3Pb+3SO2
ratio of sulphide to sulphur dioxide is 1:1
mass in 1 mole of lead sulphide=239.265
mass of lead sulphide used= 5x10^3 X1000g=5X10^6g
moles of lead sulphide=5x10^6/239.265
=20897.33moles
volume of sulphur dioxide=moles X 2.4X10^-2 =501.53 m3
Thank-you.....is it ok to combine the 2 reactions?...cuz my teacher never told us we can do that. oh and y do u use 239.265 for the mol.mass? y not (207+32=239) ?
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Third one
molecular formula is CO2.....it's very obvious....
what confusion did u have in this one....easiest of the lot
isn't compound Z also suppossed to have lead in it? (Pb, C and O) so..how wud we work out the molecular formula? nd in the Q. it tells us the mass of lead(II) oxide (11.2g)
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Z is PbCO3.....so when it is heated it decomposes to form lead oxide and carbon dioxide
yeah u can add reactions...
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Z is PbCO3.....so when it is heated it decomposes to form lead oxide and carbon dioxide
yeah u can add reactions...
but they r asking for the molecular formula of Z (PbCO3 is the empirical formula...so what will the molecular formula be?) howcome its CO2 (what happened to the Pb?)
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they r asking for the molecular formula of Z!! I'm sorry i thought they were asking for the molecular formula of the gas evolved....haste..sorry
okay so
11.2g of PbO would be 11.2/223=0.05 moles....if Z was 0.05 moles....it means their ratio is same...so molecular mass should be PbCO3..
what does the mark scheme say?
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they r asking for the molecular formula of Z!! I'm sorry i thought they were asking for the molecular formula of the gas evolved....haste..sorry
okay so
11.2g of PbO would be 11.2/223=0.05 moles....if Z was 0.05 moles....it means their ratio is same...so molecular mass should be PbCO3..
what does the mark scheme say?
hehe no problem
no, i don't have the markscheme. but the method u've shown is what i worked it out as...dunno if its correct...its 3 marks though