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Author Topic: IGCSE CHEMISTRY DOUBTS  (Read 28032 times)

Offline J.Darren

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #90 on: June 04, 2010, 12:30:49 pm »
4 a ii) Lead chloride and sodium nitrate
     iii) Silver nitrate and potassium chloride
6 b i) Add sodium hydroxide, ammonia gas given off on warming, turns damp red litmus paper blue.
7 b) Mg + 2CH3COOH ? (CH3COO)2Mg + H2

Mg - 3/24 = 1/8

CH3COOH - 12/60 = 1/5

1 : 2 mole ratio

Mg is in excess as 1/8 * 2 = 1/4, which is greater than 1/5.

Compare the mole ratio of CH3COOH to hydrogen, 2:1.

1/10 * 24 = 2.4
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Offline Ivo

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #91 on: June 04, 2010, 12:40:43 pm »
Quote from: gaurav95 on June 04, 2010, 12:21:12 pm
some more doubts coming up...............

q4aii),iii)thensame q bii

q6bi its saying ammoniuum ion and ms is giving test abt nitrate ion............

q7b whole

thx in advance........

4) a) ii) Pb(NO3)2 + 2NaCl -> PbCl2 + 2NaNO3
  
        iii) Ag+ + Cl- -> AgCl

    b) ii) Please click here.

6) b) i) Test: Add aqueous sodium hydroxide.  Result: turns damp red litmus paper blue.

7) b) i) Moles of Mg = 3/24 = 0.125
           Moles of CH3COOH = 12/60 = 0.200
           Using ratios given in the equation, to compare, divide 0.2/2 = 0.100 moles of CH3COOH.          
           Therefore, magnesium is in excess.

        ii) The one not in excess: ie. 0.1

        iii) 0.1*24 =2.4dm3

Got it?
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Offline 8T

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #92 on: June 04, 2010, 05:38:40 pm »
May june 04 q 4 b 2 why until 8 mm it .. isnt there a range ?
Plus b 3 I have no idea what is going on i need help .. could any1 help?
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Offline Ivo

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #93 on: June 04, 2010, 05:44:08 pm »
Quote from: 8T on June 04, 2010, 05:38:40 pm
May june 04 q 4 b 2 why until 8 mm it .. isnt there a range ?
Plus b 3 I have no idea what is going on i need help .. could any1 help?

Quote from: Ivo on June 03, 2010, 02:40:53 pm
OK, We know from the graph that 12cm3 of aqueous sodium hydroxide was needed to react with 4cm3 of aqueous iron(III) chloride.  Because they were all at 1.0 mol/dm3, we therefore realise that 1 mole of aqueous iron (III) chloride reacted with 3 moles of aqueous sodium hydroxide.  Therefore, the formula for the precipitate is Fe(OH)3.

For iron (II) chloride, we know the formula of the precipitate to be Fe(OH)2, and so for the same volume of aqueous iron (II) chloride - 4cm3, we know 8cm3 of sodium hydroxide was required.  Therefore, you would need to draw the maximum height of the precipitate when volume has reached 8cm3.

Hope this has helped!  ;D
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Offline jellybeans

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #94 on: June 04, 2010, 05:50:37 pm »
i've got a huge doubttt again :( :( :(
please help ! :P tttthankyou.
« Last Edit: June 04, 2010, 05:52:43 pm by jellybeans »
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Offline Ivo

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #95 on: June 04, 2010, 05:56:27 pm »
Quote from: jellybeans on June 04, 2010, 05:50:37 pm
i've got a huge doubttt again :( :( :(
please help ! :P tttthankyou.


D, obviously.  Because during the day, the plants photosynthesise, so causing oxygen levels to increase.  At night, plants and animals respire so release carbon dioxide, thus reducing the oxygen levels.
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Offline Vin

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #96 on: June 04, 2010, 05:57:26 pm »
Quote from: jellybeans on June 04, 2010, 05:50:37 pm
i've got a huge doubttt again :( :( :(
please help ! :P tttthankyou.


Is this chemistry ::) :P

i was about to answer :P

By the way which paper? I mean which session?
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Offline Ivo

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #97 on: June 04, 2010, 06:04:04 pm »
Quote from: ~VIN1094~ on June 04, 2010, 05:57:26 pm
Is this chemistry ::) :P

i was about to answer :P

By the way which paper? I mean which session?

LOLs, Bio in Chem doubts, nicely done there ~VIN1094~!  ;D
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Offline 8T

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #98 on: June 04, 2010, 06:05:05 pm »
Quote from: Ivo on June 04, 2010, 05:44:08 pm

UMM.. Honestly no it didnt u answered b 1 when i asked for b2 and 3  but i still dnt get b2 and could u have a look at b3 ..
Thanks :)
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Offline 8T

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #99 on: June 04, 2010, 06:09:26 pm »
Hi again ..
In may june 08 varient 32 4 a 2 i think ms author has accidently balanced the equation by adding 2 before the H2O
Am i Right?
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Offline Ivo

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #100 on: June 04, 2010, 06:19:52 pm »
Quote from: 8T on June 04, 2010, 06:05:05 pm
UMM.. Honestly no it didnt u answered b 1 when i asked for b2 and 3  but i still dnt get b2 and could u have a look at b3 ..
Thanks :)

That was b)ii).  Graph would level off at 8cm3.  Explained in the previous post.

Quote from: Ivo on June 03, 2010, 02:40:53 pm
OK, We know from the graph that 12cm3 of aqueous sodium hydroxide was needed to react with 4cm3 of aqueous iron(III) chloride.  Because they were all at 1.0 mol/dm3, we therefore realise that 1 mole of aqueous iron (III) chloride reacted with 3 moles of aqueous sodium hydroxide.  Therefore, the formula for the precipitate is Fe(OH)3.

For iron (II) chloride, we know the formula of the precipitate to be Fe(OH)2, and so for the same volume of aqueous iron (II) chloride - 4cm3, we know 8cm3 of sodium hydroxide was required.  Therefore, you would need to draw the maximum height of the precipitate when volume has reached 8cm3.

Hope this has helped!  ;D
« Last Edit: June 04, 2010, 06:33:11 pm by Ivo »
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Offline Ivo

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #101 on: June 04, 2010, 06:21:28 pm »
Quote from: 8T on June 04, 2010, 06:09:26 pm
Hi again ..
In may june 08 varient 32 4 a 2 i think ms author has accidently balanced the equation by adding 2 before the H2O
Am i Right?

Indeed.  the variant 1 mark scheme is right though (doesn't have the 2 in front of it).
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Offline 8T

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #102 on: June 04, 2010, 06:26:37 pm »
Could someone rexplain please may june 04 q4 b 2 ( i didnt get Ivo's explanation) and b 3 ??
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Offline 8T

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #103 on: June 04, 2010, 06:27:46 pm »
Quote from: Ivo on June 04, 2010, 06:21:28 pm
Indeed.  the variant 1 mark scheme is right though (doesn't have the 2 in front of it).
Thanks.
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Offline 8T

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #104 on: June 04, 2010, 06:31:48 pm »
May june 08 q 8 b 3 the first one my answer was N-H & C=O bonds is it correct & if not what is ?
the second one i dnt quite get what the ms says ??
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