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Author Topic: Edexcel CHEMISTRY DOUBTS!!!!  (Read 268962 times)

Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1110 on: May 22, 2011, 05:56:31 am »
Quote from: studz on May 21, 2011, 09:31:30 pm
Anyone doing chemistry unit 6?? its on the 7th of june right
i wanna know what are the key things to remember and where can i get papers for practicing
we did not do unit 6 at school  :(

Check this ;

https://studentforums.biz/pastpapers/edexcel-unit-6b-(6ch08)-practicals/
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Offline guMnam

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1111 on: May 22, 2011, 09:31:13 am »
june 2009 unit 1... q 5... how do fing the moles of so4^2- ??
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1112 on: May 22, 2011, 11:06:14 am »
Quote from: guMnam on May 22, 2011, 09:31:13 am
june 2009 unit 1... q 5... how do fing the moles of so4^2- ??

No. of ions = moles * Avogadro's constant * no. of those ions in formula
so moles = 17.1/324 = 0.05

now 0.05 * 6.02^23 * 3 (there are 3 molecules of SO4)
= 9.3 ^ 22

D is the answer
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Offline Blizz_rb93

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1113 on: May 22, 2011, 11:47:23 am »
How much energy is produced when 25cm3 of 1.0 mol dm-3 sulfuric acid is neutralized by 75cm3 of 1.0mol dm-3 NaOH given a temperature rise of 12.1 degrees Celcius?
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1114 on: May 22, 2011, 11:52:07 am »
Quote from: Blizz_rb93 on May 22, 2011, 11:47:23 am
How much energy is produced when 25cm3 of 1.0 mol dm-3 sulfuric acid is neutralized by 75cm3 of 1.0mol dm-3 NaOH given a temperature rise of 12.1 degrees Celcius?

Energy = mass * Heat capacity * temperature change
             100 * 4.12 * 12.1 = 4985.2 J

The heat capacity is given in question, its usually 4.12 or 4.18 not sure so i used 4.12
mass is 100 g as 25 + 75 = 100
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Offline guMnam

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1115 on: May 22, 2011, 01:30:56 pm »
Quote from: ang3l on May 22, 2011, 11:06:14 am
No. of ions = moles * Avogadro's constant * no. of those ions in formula
so moles = 17.1/324 = 0.05

now 0.05 * 6.02^23 * 3 (there are 3 molecules of SO4)
= 9.3 ^ 22

D is the answer
oooh.. i forgt to multipy wid three.. Thanks :)
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Offline Blizz_rb93

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1116 on: May 22, 2011, 01:31:29 pm »
thank you

i have another question

1 a) How much energy is transferred when 3.0 g MgSO4 (s) is dissolved in 45g water to give a temperature rise of 11.3 degrees Celcius?

b) How much energy is transferred per mole of MgSO4 (s)

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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1117 on: May 22, 2011, 01:40:35 pm »
Quote from: Blizz_rb93 on May 22, 2011, 01:31:29 pm
thank you

i have another question

1 a) How much energy is transferred when 3.0 g MgSO4 (s) is dissolved in 45g water to give a temperature rise of 11.3 degrees Celcius?

b) How much energy is transferred per mole of MgSO4 (s)



(a) Its the same idea
Energy = mass * Heat capacity * temperature change
             45 * 4.12 (or whatever is given) * 11.3 = 2095.02 J

(b) no. of moles of MgSO4 = m/mr
So = 3/120.4 = 0.0249

Energy per mole = energy/ moles
so 2095.02 / 0.0249 =  84137 J
u can divide by 1000 if u need the energy in KJ

If u have problem with such questions check out these notes might help u
https://studentforums.biz/revison-notes/q80boy%27s-chemistry-notes-%28edexcel%29/
(Energetics part)
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Offline guMnam

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1118 on: May 22, 2011, 01:40:52 pm »
Quote from: Blizz_rb93 on May 22, 2011, 01:31:29 pm
thank you

i have another question

1 a) How much energy is transferred when 3.0 g MgSO4 (s) is dissolved in 45g water to give a temperature rise of 11.3 degrees Celcius?

b) How much energy is transferred per mole of MgSO4 (s)


a) =45*11.3*4.18   =2125.53 j (2.13 kj)
b)

=3/120.4
=0.0249 mol

=2.13/0.0249
=85.5 kj mol-1
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Offline guMnam

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1119 on: May 22, 2011, 01:41:47 pm »
lol :P
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1120 on: May 22, 2011, 01:42:26 pm »
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Offline NightHawkerr

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1121 on: May 22, 2011, 03:32:43 pm »
Can someone explain to me the E-Z isomer stuff coming for tomorrow's exam?
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1122 on: May 22, 2011, 03:33:32 pm »
Quote from: NightHawkerr on May 22, 2011, 03:32:43 pm
Can someone explain to me the E-Z isomer stuff coming for tomorrow's exam?

http://www.chemguide.co.uk/basicorg/isomerism/geometric.html#top

Keep scrolling down.
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Offline EMO123

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1123 on: May 22, 2011, 03:35:07 pm »
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1124 on: May 22, 2011, 03:44:01 pm »
Outline an experiment to demonstrate that catalyst is not used up in a reaction? (practical details not needed)

Thx
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