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***2013 LC Chemistry Before/After***
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Acciaccatura wrote: »Oh stop, there's so many beautiful possibilities that won't happen
Found a list of good finicky questions and answers, I'll post it later. You never know, it might save 6 marks :P
Post it now please!!0 -
Quiz time again!
1. What is dative covalent bonding?A bond formed where the two shared electrons come from one atom, e.g. in the hydronium ion H3O+
2. What is the difference between heat of combustion and heat of reaction?Heat of reaction is measured in KJ, heat of combustion is measured in KJ/mol
3. Name the product formed when ethanol reacts with sodium.sodium ethoxide
4. Give an example of a reaction with an autocatalyst.Reaction of KMnO4 with Fe2+ and dilute H2SO4, autocatalyst is Mn2+
5. Why does the pH of pure water change at different temperatures?pH is measured at 25 degrees Celsius, does not give true reading outside these values
6. What is the catalyst used in the Haber process?Iron (Fe)
7. In equilibrium calculations, when does the volume of the container not matter?When there are the same number of moles of gas on either side of the equation
8. What unit is ionisation energy measured in?KJ/mol
9. In KMnO4 titrations, (i) why do you need to add sulphuric acid? (ii) What do you observe when you don't?(i) Brown colour due to MnO2 (ii) without the acid KMnO4 does not work at full oxidising power
10. Why do aldehydes and ketones have higher boiling points than corresponding alkanes?There are dipole-dipole forces present in aldehydes and ketones not present in alkanes
11. Give an example of a flocculating agent.Aluminium sulphate
This one has me snookered. Can anyone explain? 12. Why is ethanal more soluble in water than its corresponding alkane ethane?
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Acciaccatura wrote: »
This one has me snookered. Can anyone explain? 12. Why is ethanal more soluble in water than its corresponding alkane ethane?
Ethanal's carbonyl group (polar) forms hydrogen bonds in water and like all lower aldehydes, ethanal is soluble in water. Ethene is not
only temporary dipole. 0 -
Acciaccatura wrote: »
This one has me snookered. Can anyone explain? 12. Why is ethanal more soluble in water than its corresponding alkane ethane?
Would it be that hydrogen bonds form between the H and O of CHO in ethanal and the H and O in water? 0 -
Acciaccatura wrote: »Quiz time again!
1. What is dative covalent bonding?A bond formed where the two shared electrons come from one atom, e.g. in the hydronium ion H3O+
2. What is the difference between heat of combustion and heat of reaction?Heat of reaction is measured in KJ, heat of combustion is measured in KJ/mol
3. Name the product formed when ethanol reacts with sodium.sodium ethoxide
4. Give an example of a reaction with an autocatalyst.Reaction of KMnO4 with Fe2+ and dilute H2SO4, autocatalyst is Mn2+
5. Why does the pH of pure water change at different temperatures?pH is measured at 25 degrees Celsius, does not give true reading outside these values
6. What is the catalyst used in the Haber process?Iron (Fe)
7. In equilibrium calculations, when does the volume of the container not matter?When there are the same number of moles of gas on either side of the equation
8. What unit is ionisation energy measured in?KJ/mol
9. In KMnO4 titrations, (i) why do you need to add sulphuric acid? (ii) What do you observe when you don't?(i) Brown colour due to MnO2 (ii) without the acid KMnO4 does not work at full oxidising power
10. Why do aldehydes and ketones have higher boiling points than corresponding alkanes?There are dipole-dipole forces present in aldehydes and ketones not present in alkanes
11. Give an example of a flocculating agent.Aluminium sulphate
This one has me snookered. Can anyone explain? 12. Why is ethanal more soluble in water than its corresponding alkane ethane?
12 - ethanal contains the polar c=o bond and since water is polar it dissolves better in it0 -
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outnumbered wrote: »Doing a pre heat of reaction experiment calculation and cannot get the require -57 approx
Here's the question:
25 cm^3 of 1M HCL and 1M NaOH were mixed. Temp rise= 6.8k. density = 1g/cm^3 SHC = 4.2KG^-1 K^-1
calculate heat of rxn
What is this? I've never studied such a thing !
I need a solution for 2000 exam , anyone know where I can find it ?0 -
outnumbered wrote: »Doing a pre heat of reaction experiment calculation and cannot get the require -57 approx
Here's the question:
25 cm^3 of 1M HCL and 1M NaOH were mixed. Temp rise= 6.8k. density = 1g/cm^3 SHC = 4.2KG^-1 K^-1
calculate heat of rxn
Haha 2011 examcraft? Was doing that one earlier :P
Use your t2-t1 x m x c
t2-t1=6.8
m=0.05 (this is 50cm^3 converted to L by multiplying by 10^-3)
and c is given as 4.2
So when you multiply all them out you should get 1.428kJ
Then get the number of moles by multiplying 25x1 divided by 1000
This gives you 0.025 and this liberates 1.428 so 1.428 divided by 0.025 equals the heat liberated by 1 mole.
Do you have the marking scheme for that paper because I can send it on if you don't? 0 -
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weirdspider wrote: »Haha 2011 examcraft? Was doing that one earlier :P
Use your t2-t1 x m x c
t2-t1=6.8
m=0.05 (this is 50cm^3 converted to L by multiplying by 10^-3)
and c is given as 4.2
So when you multiply all them out you should get 1.428kJ
Then get the number of moles by multiplying 25x1 divided by 1000
This gives you 0.025 and this liberates 1.428 so 1.428 divided by 0.025 equals the heat liberated by 1 mole.
Do you have the marking scheme for that paper because I can send it on if you don't?
Oh Okay thanks! Remind me again why you covert to litres?
haha yeah I presume it's that paper. We just have a handout: "No.3 Questions" With all mocks/reals papers back to 75 so I actually don't know haha. Em No I don't have a solution but I only have the one questions so It's OK but thanks a million!
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mass needs to be in Kg btw, that's why they give you the density. It would be different if the density was a different number like 2. Then the mass would be 100g (0.1Kg)weirdspider wrote: »Haha 2011 examcraft? Was doing that one earlier :P
Use your t2-t1 x m x c
t2-t1=6.8
m=0.05 (this is 50cm^3 converted to L by multiplying by 10^-3)
and c is given as 4.2
So when you multiply all them out you should get 1.428kJ
Then get the number of moles by multiplying 25x1 divided by 1000
This gives you 0.025 and this liberates 1.428 so 1.428 divided by 0.025 equals the heat liberated by 1 mole.
Do you have the marking scheme for that paper because I can send it on if you don't?
Density=(mass)/(volume)0 -
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outnumbered wrote: »Oh Okay thanks! Remind me again why you covert to litres?
haha yeah I presume it's that paper. We just have a handout: "No.3 Questions" With all mocks/reals papers back to 75 so I actually don't know haha. Em No I don't have a solution but I only have the one questions so It's OK but thanks a million!
Sorry I meant kg! But you still multiply by 10^-3 anyway and its just the unit of the question. Its kind of like the ideal gas law where P must be in pascals, the volume must be in m3, same idea! And no problem 0 -
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weirdspider wrote: »Haha 2011 examcraft? Was doing that one earlier :P
Use your t2-t1 x m x c
t2-t1=6.8
m=0.05 (this is 50cm^3 converted to L by multiplying by 10^-3)
and c is given as 4.2
So when you multiply all them out you should get 1.428kJ
Then get the number of moles by multiplying 25x1 divided by 1000
This gives you 0.025 and this liberates 1.428 so 1.428 divided by 0.025 equals the heat liberated by 1 mole.
Do you have the marking scheme for that paper because I can send it on if you don't?
Ah yeah, but I'm saying if they gave you a different value for the density, the answer would be different, just to be aware at all times in the futureweirdspider wrote: »Sorry I meant kg! But you still multiply by 10^-3 anyway and its just the unit of the question. Its kind of like the ideal gas law where P must be in pascals, the volume must be in m3, same idea! And no problem 0 -
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Ah yeah, but I'm saying if they gave you a different value for the density, the answer would be different, just to be aware at all times in the future
Ohhh I know what you're saying now, thanks for reminding me. Hopefully they will keep to the 1 tomorrow in the like 90% chance that this will come up!0 -
outnumbered wrote: »Okay so does temperature need to be in K????
well technically, yes, but 1'C = 1K they just start in different places. So if they give you the heat change, then no because (20-10)'C is still equal to (293-283)'K 0 -
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outnumbered wrote: »Okay I'm so sorry but this next one wont work out either!
Here's the question:
so you have 1M 50cm cubed of HCL
temp rise= 6.5
SHC= 4.06kj kg^-1
Density = 1
Calculate (i) Heat released
(ii) Heat of reaction
I'm getting 26.39 for some reason!
(100E-3)(4.06)(6.5)=2.639Kj
Then just continue as in the other one for the heat of reaction for one mole0 -
outnumbered wrote: »Okay I'm so sorry but this next one wont work out either!
Here's the question:
so you have 1M 50cm cubed of HCL
temp rise= 6.5
SHC= 4.06kj kg^-1
Density = 1
Calculate (i) Heat released
(ii) Heat of reaction
I'm getting 26.39 for some reason!
When you were getting the number of moles did you happen to use 50cm^3 instead of 25?0 -
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