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***2013 LC Chemistry Before/After***

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12357…33

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    #122
    MarieCurie22
    Registered Users Posts: 204 ✭✭MarieCurie22


    Hamza Malik wrote: »
    So they are looking for two things.

    To supply H+ ions so the Mn7 is reduced to Mn2 ?

    I really need a B1 for chemistry :/

    Im referring to the iron tablet experiment....the KMnO4 is a purple oxidising agent, its oxidation number the of the Mn is +7 which is purple in colour however if there are not a sufficient amount of H+ ions it will only be reduced to Mn+4 which we dont want, this is a brown colour...we want the Mn+7 (purple) to go all the way to Mn+2 which is colourless.


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    #123
    woopah92
    Registered Users Posts: 482 ✭✭woopah92


    Acciaccatura wrote: »
    Form an orderly queue now :P

    Ehm, I've UCD down first because I'd like to do the premed and I just felt I'd have liked it better than Trinity. If I get medicine at all, I'd say it'll be by some miracle, like third round offers, to Galway :pac: Where are you hoping to go?

    Does anyone else feel like they're leading Galway on? I've gotten at least 3 booklets from them about medicine and they emailed my wishing me luck in my exams. :pac: I feel kinda bad cause I have no intention of going there.


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    #124
    MarieCurie22
    Registered Users Posts: 204 ✭✭MarieCurie22


    Also....for the iron tablets you could easily be asked your observations in the conical flask....
    now this could be asked in many ways they could say...
    A student noticed a brown percipitate in the conical flask explain and what could have been done to prevent it ?
    Answer: This is due to the production of Mn+4, due to lack of H+ions...to prevent this add H2So4

    Observations in the conical flask....
    Purple --> Colourless (Mn+7 -> Mn+2)
    Purple --> Brown (Mn+7 -> Mn+4)

    Also you maybe be asked why as the tiration proceeded did reaction appear to speed up?
    This is due to the production of the Mn+2 which is a catalyst (this is your example for not only auto-catalysis but homogeneous catalysis! :D


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    #125
    MarieCurie22
    Registered Users Posts: 204 ✭✭MarieCurie22


    Really watch out for this: Why dont you use HCl to provide H+ ions?

    This is due to the chlorine which is itself an oxidising agent and would affect the results drastically!


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    #126
    mocker2012
    Registered Users Posts: 36 ✭mocker2012


    Why couldn't chemistry be the first exam in the leaving cert!! I'm only doing chemistry this year, did the L.C. last year. The wait is driving me nuts, a man can only go over organic chemistry so many times!! Hopefully the organic questions won't be alkynes of trouble!!


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    #127
    MarieCurie22
    Registered Users Posts: 204 ✭✭MarieCurie22


    mocker2012 wrote: »
    Why couldn't chemistry be the first exam in the leaving cert!! I'm only doing chemistry this year, did the L.C. last year. The wait is driving me nuts, a man can only go over organic chemistry so many times!! Hopefully the organic questions won't be alkynes of trouble!!

    Nice pun :P


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    #128
    Acciaccatura
    Registered Users Posts: 428 ✭✭Acciaccatura


    woopah92 wrote: »
    Does anyone else feel like they're leading Galway on? I've gotten at least 3 booklets from them about medicine and they emailed my wishing me luck in my exams. :pac: I feel kinda bad cause I have no intention of going there.

    Yeah, no other college me has contacted me as much as they have, I feel so loved by them :pac: btw, does anyone know if I can put medicine in Cork down on my CAO now? I hadn't put it on previous, but I've done the HPAT n' stuff, so hopefully it's not too late?


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    #129
    MarieCurie22
    Registered Users Posts: 204 ✭✭MarieCurie22


    Acciaccatura wrote: »
    Yeah, no other college me has contacted me as much as they have, I feel so loved by them :pac: btw, does anyone know if I can put medicine in Cork down on my CAO now? I hadn't put it on previous, but I've done the HPAT n' stuff, so hopefully it's not too late?

    No is a restrictive entry course must have been down by the 1st closing date :/


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    #130
    Acciaccatura
    Registered Users Posts: 428 ✭✭Acciaccatura


    MarieCurie22 wrote: »
    No is a restrictive entry course must have been down by the 1st closing date :/

    Ah sure not to worry, I'd rather Galway if I'd to travel across the country anyway, thanks! :)


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    #131
    weirdspider
    Registered Users Posts: 346 ✭✭weirdspider


    How can you determine how many lone pairs a molecule has? Last year I noticed they put up PH3 and asked what shape of molecule it was. Its pyramidal according to the marking scheme but how does one know its not triangular planar?


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    #132
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    weirdspider wrote: »
    How can you determine how many lone pairs a molecule has? Last year I noticed they put up PH3 and asked what shape of molecule it was. Its pyramidal according to the marking scheme but how does one know its not triangular planar?

    By Hund's Rule of Maximum Multiplicity. Phosporus has 15 electrons. 2 in the first shell, 8 in the second and 5 in the 3. There is 4 sub-energy levels in the 3rd shell. Each electron will fill one singly but the 5th is forced to share with one of the previous electrons.


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    #133
    weirdspider
    Registered Users Posts: 346 ✭✭weirdspider


    Deleted User wrote: »
    By Hund's Rule of Maximum Multiplicity. Phosporus has 15 electrons. 2 in the first shell, 8 in the second and 5 in the 3. There is 4 sub-energy levels in the 3rd shell. Each electron will fill one singly but the 5th is forced to share with one of the previous electrons.

    But how do you know? I thought the number of the shell dictates the number of orbitals so theres 4 sublevels in the 4th shell?


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    #134
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    weirdspider wrote: »
    But how do you know? I thought the number of the shell dictates the number of orbitals so theres 4 sublevels in the 4th shell?

    Well it's just something you learn I guess.
    Like the first shell has a sub-level s
    Then the second shell had an s and a p orbital. But the p orbital has 3 sub-levels again px py and pz, each can hold 2.
    Then there is a 3s, 3p and then a 3d orbital. The d orbital can hold 10 electrons.


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    #135
    MarieCurie22
    Registered Users Posts: 204 ✭✭MarieCurie22


    For showing the ethanoic acid (produced in the organic chemistry reflux experiment) is an acid, is it ok to use the CaCO3 example rather than the Na2CO3? And just say fizzing observed and CO2 is given off therefore it is an acid?


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    #136
    AB2013
    Registered Users Posts: 18 ✭AB2013


    MarieCurie22 wrote: »
    For showing the ethanoic acid (produced in the organic chemistry reflux experiment) is an acid, is it ok to use the CaCO3 example rather than the Na2CO3? And just say fizzing observed and CO2 is given off therefore it is an acid?

    Yeah because Acid + Sulphate ---> Salt + water + carbon dioxide

    :)


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    #137
    MarieCurie22
    Registered Users Posts: 204 ✭✭MarieCurie22


    AB2013 wrote: »
    Yeah because Acid + Sulphate ---> Salt + water + carbon dioxide

    :)

    Uhm what? That explains nothing? Acid plus sulphate? Wheres the sulphate coming from? Dealing with ethanoic acid? And Limestone?


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    #138
    AB2013
    Registered Users Posts: 18 ✭AB2013


    MarieCurie22 wrote: »
    Uhm what? That explains nothing? Acid plus sulphate? Wheres the sulphate coming from? Dealing with ethanoic acid? And Limestone?

    Hahaha woops my brain is fried! I meant carbonate :D


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    #139
    weirdspider
    Registered Users Posts: 346 ✭✭weirdspider


    Deleted User wrote: »
    Well it's just something you learn I guess.
    Like the first shell has a sub-level s
    Then the second shell had an s and a p orbital. But the p orbital has 3 sub-levels again px py and pz, each can hold 2.
    Then there is a 3s, 3p and then a 3d orbital. The d orbital can hold 10 electrons.

    Ah I get it now. Thanks!


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    #140
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    weirdspider wrote: »
    Ah I get it now. Thanks!

    Are you sure? I know I'm not very good at explaining things! :(


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    #141
    weirdspider
    Registered Users Posts: 346 ✭✭weirdspider


    Deleted User wrote: »
    Are you sure? I know I'm not very good at explaining things! :(

    Yup! 2 electrons occupy 2 orbitals, there are 15 electrons in P so this leaves 1 lone electron. Right?


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    #142
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    weirdspider wrote: »
    Yup! 2 electrons occupy 2 orbitals, there are 15 electrons in P so this leaves 1 lone electron. Right?

    Here, I drew this :P I thought it might explain it better :P


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    #143
    MarieCurie22
    Registered Users Posts: 204 ✭✭MarieCurie22


    Deleted User wrote: »
    Here, I drew this :P I thought it might explain it better :P
    If you have chemistry live theres a table in the chapter on bonding :D thats just perfect really.
    In recent times they have been giving things like what are the possible shapes of AB2
    So easiest way i find is to go what molecules do i know of that have 2 of one element and one of the other...H2O and CO2....which are v-shaped and linear...:D


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    #144
    MarieCurie22
    Registered Users Posts: 204 ✭✭MarieCurie22


    Btw you guys do know you can use the periodic table to tell you how many pairs in the outermost shell right?
    If you count across the period...it tells you how many electrons in the outermost shell! Lets take for example....Carbon...

    -Ok so locate the line going across in which Carbon (C) can be found...

    -Its in the second line/period from the top...this tells us there are 2 shells in a carbon atom.

    -Then we count which group it is in by counting the elements between group one and Carbons group...

    -So we count...Li (1), Be (2), B(3), C(4)...

    -This tells us there are four electrons in the outermost shell of carbon.

    So if asked the shape of CH4 you draw a big C and place 4 dots around it...

    You then need to find the valency (number of outer electrons to be shared) in Hydrogen..it is in group 1 period 1 telling us it has one shell with one outer electron it needs 1 more electron to comply with the octect rule...so we have 4 Hydrogens which need one more electron each and 1 carbon with 4 electrons each needing one to have a shell with 8.

    -Each H takes an electron to pair with :) equallly space these and voila!


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    #145
    Inspector Coptoor
    Registered Users Posts: 6,818 ✭✭✭Inspector Coptoor


    MarieCurie22 wrote: »
    Btw you guys do know you can use the periodic table to tell you how many pairs in the outermost shell right?
    If you count across the period...it tells you how many electrons in the outermost shell! Lets take for example....Carbon...

    -Ok so locate the line going across in which Carbon (C) can be found...

    -Its in the second line/period from the top...this tells us there are 2 shells in a carbon atom.

    -Then we count which group it is in by counting the elements between group one and Carbons group...

    -So we count...Li (1), Be (2), B(3), C(4)...

    -This tells us there are four electrons in the outermost shell of carbon.

    So if asked the shape of CH4 you draw a big C and place 4 dots around it...

    You then need to find the valency (number of outer electrons to be shared) in Hydrogen..it is in group 1 period 1 telling us it has one shell with one outer electron it needs 1 more electron to comply with the octect rule...so we have 4 Hydrogens which need one more electron each and 1 carbon with 4 electrons each needing one to have a shell with 8.

    -Each H takes an electron to pair with :) equallly space these and voila!

    That's Junior Cert covalent bonding explained well.

    Surely you've got the shape & structure if methane clear in your head for the last 3-; years?


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    #146
    randylonghorn
    Moderators, Education Moderators Posts: 29,509 Mod ✭✭✭✭randylonghorn


    Scuid Mhór wrote: »
    Marry me?!
    outnumbered wrote: »
    Back off, she's mine!
    Typical lads, offer to marry a girl if she gives them what they want!

    But after the exam is over ... ;)


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    #147
    simons545
    Registered Users Posts: 90 ✭✭simons545


    MarieCurie22 wrote: »
    For showing the ethanoic acid (produced in the organic chemistry reflux experiment) is an acid, is it ok to use the CaCO3 example rather than the Na2CO3? And just say fizzing observed and CO2 is given off therefore it is an acid?
    I presume you're referencing the experiment with the dichromate salts we can't do. I'm not 100% sure if that would be acceptable because an acidic oxide, like Sulphur dioxide will neutralise a base the same way an acid will, but to the extend of my knowledge is not an acid itself until in solution.
    If I was doing that question I would write out the reaction equation for its reaction with Na2CO3 or CaCO3 and then explain why carboxylic acids are acids. They lose a H+ due to the stability of the carboxylate ion, (C=OO-), and form an area of electronegativity.
    I presume if you wrote down the reaction equation and that, because CO2 is evolved/produced in the reaction along with a salt and water, it could be classed as a neutralisation reaction.
    Here's the reaction equation for the Na2CO3:
    2CH3COOH+Na2CO3-->2CH3COONa+CO2+H20

    and the CaCO3:
    2CH3COOH+CaCO3-->(CH3COO)2Ca+CO2+H20

    hope this helped somewhat :D


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    #148
    weirdspider
    Registered Users Posts: 346 ✭✭weirdspider


    Deleted User wrote: »
    Here, I drew this :P I thought it might explain it better :P

    Haha thanks appreciate the hassle! Yes I get it now :D


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    #149
    Isco
    Registered Users Posts: 127 ✭✭Isco


    reading through this thread makes me realise how little I know


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    #150
    0mega
    Registered Users Posts: 850 ✭✭✭0mega


    Does anyone have the Principle and processes of paper chromotography? Not in my book


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    #151
    weirdspider
    Registered Users Posts: 346 ✭✭weirdspider


    0mega wrote: »
    Does anyone have the Principle and processes of paper chromotography? Not in my book

    Different components of a mixture are attracted by different extents to the stationary/mobile phases


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