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Author Topic: chem question  (Read 9496 times)

nid404

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Re: chem question
« Reply #45 on: September 30, 2009, 06:00:32 pm »
No change....cuz sodium sulphate is a salt...so it's neutral
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Q80BOY

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Re: chem question
« Reply #46 on: September 30, 2009, 06:02:59 pm »
Quote from: nid404 on September 30, 2009, 06:00:32 pm
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!  ;)

« Last Edit: October 03, 2009, 04:52:24 pm by Q80BOY »
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Offline Ghost Of Highbury

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Re: chem question
« Reply #47 on: September 30, 2009, 06:03:24 pm »
sodium sulfate is a salt therefore no change
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nid404

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Re: chem question
« Reply #48 on: September 30, 2009, 06:04:53 pm »
Quote from: Q80BOY on September 30, 2009, 06:02:59 pm
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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Q80BOY

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Re: chem question
« Reply #49 on: September 30, 2009, 06:05:44 pm »
Quote from: eddie_adi619 on September 30, 2009, 06:03:24 pm
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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Offline Ghost Of Highbury

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Re: chem question
« Reply #50 on: September 30, 2009, 06:10:34 pm »
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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Q80BOY

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Re: chem question
« Reply #51 on: September 30, 2009, 06:13:14 pm »
ahaaa .. i get it .. thanks adii!!  ;)
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Offline Ghost Of Highbury

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Re: chem question
« Reply #52 on: September 30, 2009, 06:14:16 pm »
anytime dude...!!
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Offline Bani

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Re: chem question
« Reply #53 on: October 01, 2009, 09:57:12 pm »
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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nid404

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Re: chem question
« Reply #54 on: October 02, 2009, 06:10:38 am »
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


« Last Edit: October 02, 2009, 08:50:53 am by nid404 »
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nid404

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Re: chem question
« Reply #55 on: October 02, 2009, 06:15:32 am »
                       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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nid404

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Re: chem question
« Reply #56 on: October 02, 2009, 06:18:39 am »
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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Offline Bani

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Re: chem question
« Reply #57 on: October 02, 2009, 03:30:09 pm »
Quote from: nid404 on October 02, 2009, 06:10:38 am
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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Offline Bani

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Re: chem question
« Reply #58 on: October 02, 2009, 03:32:44 pm »
Quote from: nid404 on October 02, 2009, 06:18:39 am
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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nid404

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Re: chem question
« Reply #59 on: October 02, 2009, 04:06:50 pm »
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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