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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by James A)
    I said that we should split the excess iodine (that we had to titrate) into seperate beakers, so more titrations can be carried out, hence a mean titre can be obtained.
    That will increase reliability (reduce random error) but I think the question emphasized on systematic error.
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    titration 17.5%
    colour change? for the iodine, without indicator?
    ppm 2000>60
    titre uncertainty 2x+/-
    Sn1- mechanism, george facer states that secondary mainly follow this mechanism.
    other test? flame test?
    Last question- anthropogenic change induced by human activity, hence transportation, distribution, extraction contribute to emissions of co2 from fossil fuels, water concentration in the atmosphere constant. Co2 attributes to increased greenhouse effect, hence more heat radiated, polar ice caps melt, sea levels rise, severe shortages of food and fresh water. natural change??
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    (Original post by airheadbuster)
    That will increase reliability (reduce random error) but I think the question emphasized on systematic error.
    There was a pastpaper question about this...

    it was like "how was the reliabilty inproved" and "how was the accurace reduced" when it was divided into portions...
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    (Original post by StUdEnTIGCSE)
    There was a pastpaper question about this...

    it was like "how was the reliabilty inproved" and "how was the accurace reduced" when it was divided into portions...
    Ya, Jan 2010.
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    (Original post by dyingbreed)
    titration 17.5%
    colour change? for the iodine, without indicator?
    ppm 2000>60
    titre uncertainty 2x+/-
    Sn1- mechanism, george facer states that secondary mainly follow this mechanism.
    other test? flame test?
    Last question- anthropogenic change induced by human activity, hence transportation, distribution, extraction contribute to emissions of co2 from fossil fuels, water concentration in the atmosphere constant. Co2 attributes to increased greenhouse effect, hence more heat radiated, polar ice caps melt, sea levels rise, severe shortages of food and fresh water. natural change??
    Yellow to colourless or red brown to colourless.
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    (Original post by airheadbuster)
    That will increase reliability (reduce random error) but I think the question emphasized on systematic error.
    ?

    There were two particular questions at the end of the whole titration section (excluding the one about the indicator colour)

    One was about how we could improve the reliability, the other was what was the source of error. Correct me if I'm wrong on this.
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    SF6
    CCL4
    2-chlorobutane
    Potassium nitrate
    Ozone depletion
    X = The most common energy of the molecules
    Hydration enthalpy

    Ba(s) + 2H2O(l) ==> Ba(OH)2(aq) +H2(g)
    (Redox reaction) Ba increases in oxidation number from 0 to +2 and H changed from +1 to 0 (in H2)
    White solid – as BaSO4 is insoluble.

    MgCO3 decomposes more quickly than BaCO3, shown by limewater turning cloudy more quickly or gas produced more quickly
    Flame Test;
    MgCO3 – no flame colour
    BaCO3 – Apple-Green/Green flame colour

    Calculations :
    =0.00116
    =0.00058
    =0.0125
    =0.01192
    =13.8% (3s.f.)

    Percentage error : 0.86%

    NaOH dissolved in ethanol
    Elimination reaction
    SN1 mechanism, although may go by SN2 (but slower).


    18 Electrons
    London Forces
    (Both have London forces) but one has higher boiling point due to Permanent dipoles, which are stronger.
    There is Hydrogen bonding in HF , Hydrogen bonding is the strongest intermolecular force, more energy required to separate the molecules.

    Cl atom too large/Not electronegative enough, to form Hydrogen bonds.

    2,200ppm>60ppm, thus 2.2g dm^-3 is greater than 60ppm
    More carbonate ions, equilibrium position moves to the right to remove extra carbonate ions, thus less CO2 produced.

    Vibration changes polarity of bonds
    Absorb IR resulting in UV radiation to become trapped in the atmosphere when they are emitted off the earth.

    Bases deprotonate thus not being able to be attacked by the nucleophile (H20)
    Increase in temperature favours the forward reaction (as endothermic), thus equilibrium position moves to the right, thus rate of hydrolysis increases.

    Forward reaction=Backward reaction
    No change in concentration

    Scientists are more worried about Carbon Dioxide than water vapour as Carbon Dioxide is present in higher concentrations in the atmosphere. Anthropogenic climate change is due to human activities eg burning of fossil fuels. Burning of fossil fuels is increases, so levels of carbon dioxide in the atmosphere is likely to continue increasing. Natural climate change may be causes by natural processes such as the formation of carbonates in rocks that remove CO2 in longer durations.
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    (Original post by Al_Chemist)
    SF6
    CCL4
    2-chlorobutane
    Potassium nitrate
    Ozone depletion
    X = The most common energy of the molecules
    Hydration enthalpy

    Ba(s) + 2H2O(l) ==> Ba(OH)2(aq) +H2(g)
    (Redox reaction) Ba increases in oxidation number from 0 to +2 and H changed from +1 to 0 (in H2)
    White solid – as BaSO4 is insoluble.

    MgCO3 decomposes more quickly than BaCO3, shown by limewater turning cloudy more quickly or gas produced more quickly
    Flame Test;
    MgCO3 – no flame colour
    BaCO3 – Apple-Green/Green flame colour

    Calculations :
    =0.00116
    =0.00058
    =0.0125
    =0.01192
    =13.8% (3s.f.)

    Percentage error : 0.86%

    NaOH dissolved in ethanol
    Elimination reaction
    SN1 mechanism, although may go by SN2 (but slower).


    18 Electrons
    London Forces
    (Both have London forces) but one has higher boiling point due to Permanent dipoles, which are stronger.
    There is Hydrogen bonding in HF , Hydrogen bonding is the strongest intermolecular force, more energy required to separate the molecules.

    Cl atom too large/Not electronegative enough, to form Hydrogen bonds.

    2,200ppm>60ppm, thus 2.2g dm^-3 is greater than 60ppm
    More carbonate ions, equilibrium position moves to the right to remove extra carbonate ions, thus less CO2 produced.

    Vibration changes polarity of bonds
    Absorb IR resulting in UV radiation to become trapped in the atmosphere when they are emitted off the earth.

    Bases deprotonate thus not being able to be attacked by the nucleophile (H20)
    Increase in temperature favours the forward reaction (as endothermic), thus equilibrium position moves to the right, thus rate of hydrolysis increases.

    Forward reaction=Backward reaction
    No change in concentration

    Scientists are more worried about Carbon Dioxide than water vapour as Carbon Dioxide is present in higher concentrations in the atmosphere. Anthropogenic climate change is due to human activities eg burning of fossil fuels. Burning of fossil fuels is increases, so levels of carbon dioxide in the atmosphere is likely to continue increasing. Natural climate change may be causes by natural processes such as the formation of carbonates in rocks that remove CO2 in longer durations.

    umm for the question about mgco3 and baco3, i said add sodium sulfate solution since it said no acid. so mgso4 would dissolve, and baso4 would be insoluble. do u think i'd get the mark?
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    What about the colour change for the titration?
    Was it yellow to colourless or the other way around? Because the end produce was Iodine, not Iodine ions as it normally is?....
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    (Original post by daniya12)
    What about the colour change for the titration?
    Was it yellow to colourless or the other way around? Because the end produce was Iodine, not Iodine ions as it normally is?....
    I put pale yellow to colourless


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    (Original post by kabOOmm)
    umm for the question about mgco3 and baco3, i said add sodium sulfate solution since it said no acid. so mgso4 would dissolve, and baso4 would be insoluble. do u think i'd get the mark?
    As long as it can differentiate between the two, then probably yes.
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    (Original post by Al_Chemist)
    SF6
    CCL4
    2-chlorobutane
    Potassium nitrate
    Ozone depletion
    X = The most common energy of the molecules
    Hydration enthalpy

    Ba(s) + 2H2O(l) ==> Ba(OH)2(aq) +H2(g)
    (Redox reaction) Ba increases in oxidation number from 0 to +2 and H changed from +1 to 0 (in H2)
    White solid – as BaSO4 is insoluble.

    MgCO3 decomposes more quickly than BaCO3, shown by limewater turning cloudy more quickly or gas produced more quickly
    Flame Test;
    MgCO3 – no flame colour
    BaCO3 – Apple-Green/Green flame colour

    Calculations :
    =0.00116
    =0.00058
    =0.0125
    =0.01192
    =13.8% (3s.f.)

    Percentage error : 0.86%

    NaOH dissolved in ethanol
    Elimination reaction
    SN1 mechanism, although may go by SN2 (but slower).


    18 Electrons
    London Forces
    (Both have London forces) but one has higher boiling point due to Permanent dipoles, which are stronger.
    There is Hydrogen bonding in HF , Hydrogen bonding is the strongest intermolecular force, more energy required to separate the molecules.

    Cl atom too large/Not electronegative enough, to form Hydrogen bonds.

    2,200ppm>60ppm, thus 2.2g dm^-3 is greater than 60ppm
    More carbonate ions, equilibrium position moves to the right to remove extra carbonate ions, thus less CO2 produced.

    Vibration changes polarity of bonds
    Absorb IR resulting in UV radiation to become trapped in the atmosphere when they are emitted off the earth.

    Bases deprotonate thus not being able to be attacked by the nucleophile (H20)
    Increase in temperature favours the forward reaction (as endothermic), thus equilibrium position moves to the right, thus rate of hydrolysis increases.

    Forward reaction=Backward reaction
    No change in concentration

    Scientists are more worried about Carbon Dioxide than water vapour as Carbon Dioxide is present in higher concentrations in the atmosphere. Anthropogenic climate change is due to human activities eg burning of fossil fuels. Burning of fossil fuels is increases, so levels of carbon dioxide in the atmosphere is likely to continue increasing. Natural climate change may be causes by natural processes such as the formation of carbonates in rocks that remove CO2 in longer durations.
    What was the question to SF6?
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    (Original post by daniya12)
    What was the question to SF6?
    Smallest bond angle
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    (Original post by Al_Chemist)
    As long as it can differentiate between the two, then probably yes.

    it can't really. but it said no heatt!! so i was like, flame test does produce heat. i dont knoww, i was so confused
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    (Original post by kabOOmm)
    umm for the question about mgco3 and baco3, i said add sodium sulfate solution since it said no acid. so mgso4 would dissolve, and baso4 would be insoluble. do u think i'd get the mark?
    I didn't actually think of that, seems a good guess to me!
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    (Original post by James A)
    I didn't actually think of that, seems a good guess to me!
    thanks! but it's probably wrong because you cant really differentiate between the two. :/
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    (Original post by Al_Chemist)
    SF6
    CCL4
    2-chlorobutane
    Potassium nitrate
    Ozone depletion
    X = The most common energy of the molecules
    Hydration enthalpy

    Ba(s) + 2H2O(l) ==> Ba(OH)2(aq) +H2(g)
    (Redox reaction) Ba increases in oxidation number from 0 to +2 and H changed from +1 to 0 (in H2)
    White solid – as BaSO4 is insoluble.

    MgCO3 decomposes more quickly than BaCO3, shown by limewater turning cloudy more quickly or gas produced more quickly
    Flame Test;
    MgCO3 – no flame colour
    BaCO3 – Apple-Green/Green flame colour

    Calculations :
    =0.00116
    =0.00058
    =0.0125
    =0.01192
    =13.8% (3s.f.)

    Percentage error : 0.86%

    NaOH dissolved in ethanol
    Elimination reaction
    SN1 mechanism, although may go by SN2 (but slower).


    18 Electrons
    London Forces
    (Both have London forces) but one has higher boiling point due to Permanent dipoles, which are stronger.
    There is Hydrogen bonding in HF , Hydrogen bonding is the strongest intermolecular force, more energy required to separate the molecules.

    Cl atom too large/Not electronegative enough, to form Hydrogen bonds.

    2,200ppm>60ppm, thus 2.2g dm^-3 is greater than 60ppm
    More carbonate ions, equilibrium position moves to the right to remove extra carbonate ions, thus less CO2 produced.

    Vibration changes polarity of bonds
    Absorb IR resulting in UV radiation to become trapped in the atmosphere when they are emitted off the earth.

    Bases deprotonate thus not being able to be attacked by the nucleophile (H20)
    Increase in temperature favours the forward reaction (as endothermic), thus equilibrium position moves to the right, thus rate of hydrolysis increases.

    Forward reaction=Backward reaction
    No change in concentration

    Scientists are more worried about Carbon Dioxide than water vapour as Carbon Dioxide is present in higher concentrations in the atmosphere. Anthropogenic climate change is due to human activities eg burning of fossil fuels. Burning of fossil fuels is increases, so levels of carbon dioxide in the atmosphere is likely to continue increasing. Natural climate change may be causes by natural processes such as the formation of carbonates in rocks that remove CO2 in longer durations.
    Why is the % error 0.86%
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    (Original post by Hi, How are you ?)
    Why is the % error 0.86%
    Because that was the answer.

    What do you mean, 'why'?
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    (Original post by James A)
    Because that was the answer.

    What do you mean, 'why'?
    Isn't it 0.43 % :confused:
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    (Original post by Hi, How are you ?)
    Isn't it 0.43 % :confused:
    Initial and final reading therefore total uncertainty is 2 times the uncertainty


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