ELECTROLYSIS OF IMPURE Cu........
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Q.1 The eletrolysis of impure copper is carried out using CuSO4 as electrolyte, copper being pure Cu, while anode as Impure Cu.
The three observations are :
A) Anode dissolves
B) The mass of cathode increases
C) the blue color of solution fades.
Is the third observation correct??
Q.2 What impurities are present in impure Copper?
Q.3 What if the electrolyte is Copper nitrate?
Q.4 What will be the products left after this electrolysis is carried out? I mean the salts which are left behind.
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Incorrect. Any changes to [Cu2+] are negligible, as far as 'O' and 'A' levels are concerned.
Other metal ions, both more electropositive and less electropositive, than copper.
No difference, as sulfate(VI) and nitrate(V) anions both have their heteroatoms already in their most positive OS possible, and cannot be oxidized further at the anode (to which they are electrostatically attracted).
Depends on the specific impurities present. Less electropositive metal ions are reduced at the cathode, while more electropositive metal ions remained in the aqueous oxidized state.
Originally posted by hoay:Q.1 The eletrolysis of impure copper is carried out using CuSO4 as electrolyte, copper being pure Cu, while anode as Impure Cu.
The three observations are :
A) Anode dissolves
B) The mass of cathode increases
C) the blue color of solution fades.
Is the third observation correct??
Q.2 What impurities are present in impure Copper?
Q.3 What if the electrolyte is Copper nitrate?
Q.4 What will be the products left after this electrolysis is carried out? I mean the salts which are left behind.
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How this observation is incorrect, since as electrolysis progresses the [Cu2+] decreases and the concentration of impurities [the metal ions increaese] so the blue color should fade. Can you explain your answer Sir?
Secondly, is their any book or past paper where you have found this written?
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How this observation is incorrect, since as electrolysis progresses the [Cu2+] decreases and the concentration of impurities [the metal ions increaese] so the blue color should fade. Can you explain your answer Sir?
Secondly, is their any book or past paper where you have found this written?
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How this observation is incorrect, since as electrolysis progresses the [Cu2+] decreases and the concentration of impurities [the metal ions increaese] so the blue color should fade. Can you explain your answer Sir?
Secondly, is their any book or past paper where you have found this written?
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How this observation is incorrect, since as electrolysis progresses the [Cu2+] decreases and the concentration of impurities [the metal ions increaese] so the blue color should fade. Can you explain your answer Sir?
Secondly, is their any book or past paper where you have found this written?
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Impurities are essentially :
other metals which are less electropositive than Cu
and
other metals which are more electropositive than Cu
The former are mostly already in their reduced state (eg. Ag, Au, etc), and simply drop to the bottom as anodic sludge.
The latter are mostly already in their oxidized state (eg. Fe2+, Al3+, etc), and simply dissolve into the electrolyte solution.
Notice that both groups do not take part in any redox reaction at the anode, and therefore do not deprive the Cu (at the impure anode) from being oxidized at the anode.
Hence, at the anode, Cu is being oxidized to Cu2+, for every 2 moles of electrons transferred.
At the cathode, only Cu2+ is being reduced to Cu (as more electropositive metals, eg. Fe2+, Al3+, etc) prefer to remain in their oxidized, aqueous state.
Hence, at the cathode, Cu2+ is being reduced to Cu, for every 2 moles of electrons transferred.
Therefore, the [Cu2+] in the electrolyte solution remains almost unchanged (barring negligible factors such as evaporation of solvent, negligible oxidation of impurities closely similar to Cu in electropositivity, etc; all of which are not the concern of the 'O' or 'A' levels).
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Energy is the capacity of doing work. Enthalpy is the total heat content of a system. What is the difference between energy and enthalpy??
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Originally posted by hoay:
Energy is the capacity of doing work. Enthalpy is the total heat content of a system. What is the difference between energy and enthalpy??
For 'A' level Chemistry purposes, there is no difference, and Cambridge will accept either term.Eg.
"bond dissociation enthalpy" = "bond dissociation energy",
"bond formation enthalpy" = "bond formation energy",
"lattice dissociation enthalpy" = "lattice dissociation energy",
"lattice formation enthalpy" = "lattice formation energy",
etc.
FYI, at higher levels, although there are several different ways to define the technical difference between enthalpy and energy, but for 'A' level Chemistry purposes, it'll more than suffice for the interested student to take it that :
Energy change is heat change under constant volume.
Enthalpy change is heat change under constant pressure.
For most chemical reactions, to 3 significant figures, there is negligible difference between the enthalpy change and energy change values, and thus Cambridge accepts either term used interchangeably.
Ideally when applying Hess Law, it's still good practice (though not compulsory) to standardize all processes in the cycle, in either "enthalpy" or "energy" values, rather than a mixture of both.
(Similarly, "Oxidation Number" versus "Oxidation State"; there is a technical difference at higher levels, but not for 'A' level Chemistry purposes).
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But what do you eman by the statement that "enathalpy is the total heat content of a system."Does this mean all type of energies contained by a system viz. Potentilalenergy, Kinetic energy, vibrational energy, rotational energy?
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Originally posted by hoay:
But what do you eman by the statement that "enathalpy is the total heat content of a system."Does this mean all type of energies contained by a system viz. Potentilalenergy, Kinetic energy, vibrational energy, rotational energy?
All the energies you've mentioned, are included in both "enthalpy" and "energy", but "enthalpy" also measures the system's volume and pressure.If you need to discuss this further, please visit a dedicated physics or chemistry forum, because anything beyond what's required for A level Chemistry (specifically the Singapore H2 syllabus) is not within my personal interest to discuss.
Of course, anyone else reading this thread (whether you be of physics or chemistry background), feel free to continue this discussion with Hoay if you wish.
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Thank you very much sir.
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Originally posted by hoay:
Thank you very much sir.
You're totally welcome, Hoay.
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When considering the electron pairs repulsion in a molecule why does a lone pair of elctrons repel more strongly than a bonding pair??
Is it due to that a lone pair in controlled by one atom..
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Originally posted by hoay:
When considering the electron pairs repulsion in a molecule why does a lone pair of elctrons repel more strongly than a bonding pair??
Is it due to that a lone pair in controlled by one atom..
Hi again Hoay, in future, pls try to start a new thread when asking an old qn, instead of using an old thread whose title is unrelated to ur new qn, thanks.For A level purposes, it should be regarded and imagined that a lone pair of electrons is positioned 'horizontally' (ie. both electrons equally close to the atom's nucleus) and thus occupies more space that is in closer proximity to the nucleus, and hence experiences greater repulsions with the other electron pairs around the atom, compared to bond pairs which are positioned 'vertically' away from the nucleus (ie. the dot closer to one atom, and the cross nearer to the other atom bonded with; in fact, this is how Cambridge prefers A level students to draw their dot-and-cross diagrams, as opposed to how some schools erroneously teach), and thus the bond pair's repulsion is 'shared' between (repelling) electrons of both atoms, and hence lesser in magnitude, compared to the repulsion that occurs between lone pairs and other electron pairs of the atom.
As an illustrative analogy, imagine you're on the MRT train.
The passengers standing upright holding onto (ie. bonded to) the overhead support handles represent the bond pairs, while the passengers lying down on the floor, not bonded to the overhead support handles, represent the lone pairs.
Obviously, the passengers lying down on the train floor (ie. the lone pairs), would occupy more floor space, annoying and repelling other passengers to a greater extent, compared to the passengers standing upright (ie. the bond pairs).