Originally posted by Flying grenade:HCO3- is both amphoteric and amphiprotic right?
Originally posted by Flying grenade:I understand this :
By Hess law,
🔺Hsoln = 🔺Hhyd + 🔺LEdissociation
Can help me check where i've gone wrong thinking in this way?? :
🔺Hsoln = energy released on hydration by hydrated ions Minus Energy absorbed by Ionic solid to dissociate
So 🔺Hsoln = (-ve enthalpy change) minus (positive enthalpy change )
If i put modulus on the RHS terms, then it becomes all +ve
Help please thanks!
Hence, without worrying about which magnitude outweighs which, you should simply add up the endothermic lattice dissociation enthalpy change (ie. positive value) with the exothermic hydration enthalpy change (ie. negative value) to obtain solution enthalpy change, which could be either endothermic or exothermic (ie. positive or negative value).
Okay got it, thanks !!
Hi, I need help for this question. Adopted from MJC tutorial.
"Graphite is one of the allotropes of carbon. The graphite structure consists of hexagonal layers. Each carbon atom has one electron that can be delocalized parallel to the layers to make graphite a good electrical conductor.
Different atoms can be fitted in between the layers of carbon atoms to produce an usual set of “graphite compounds”. When the graphite lattice contains atoms of alkali metal such as caesium, then a bronze-coloured solid is formed which has a greater conductivity than pure graphite.
In hexagonal boron nitride , the structure is composed of layers of hexagonal B3N3 ring. The boron atom utilizes all the three valence electrons to form covalent bonds with three neighbouring nitrogen atoms. Each nitrogen atom still has a lone pair of electrons which it utilizes to form a dative bond with an adjacent boron atom. Although graphite and hexagonal boron nitride have similar structures, they differ in electrical conductivity. Unlike graphite, boron nitride is an insulator.
When heated under pressure, this form of boron nitride is converted into another form which is an extremely hard solid .
(g)(i) Suggest and describe the structure adopted by the new material formed"
Originally posted by MightyBiscuits:Hi, I need help for this question. Adopted from MJC tutorial.
"Graphite is one of the allotropes of carbon. The graphite structure consists of hexagonal layers. Each carbon atom has one electron that can be delocalized parallel to the layers to make graphite a good electrical conductor.
Different atoms can be fitted in between the layers of carbon atoms to produce an usual set of “graphite compounds�. When the graphite lattice contains atoms of alkali metal such as caesium, then a bronze-coloured solid is formed which has a greater conductivity than pure graphite.
In hexagonal boron nitride , the structure is composed of layers of hexagonal B3N3 ring. The boron atom utilizes all the three valence electrons to form covalent bonds with three neighbouring nitrogen atoms. Each nitrogen atom still has a lone pair of electrons which it utilizes to form a dative bond with an adjacent boron atom. Although graphite and hexagonal boron nitride have similar structures, they differ in electrical conductivity. Unlike graphite, boron nitride is an insulator.
When heated under pressure, this form of boron nitride is converted into another form which is an extremely hard solid .
(g)(i) Suggest and describe the structure adopted by the new material formed"
Hi Ultima, i have some queries
Page 97 cs toh advanced guide
Btm of the page "C=O bond energy in CO2 is significantly stronger than average bond energies given in data booklet"
My initial thought was , all C=O bonds, all C-H bonds are the same? Apparently not
I thought, the average bond energies arises from page 96 top of the page , because bond energies can be derived from 🔺Hformation and 🔺H atomisation
Is the reason that why not all C-H or C=O bonds are the same, because the C or O atom might be attached to another (different) atoms in different compounds?
Thanks for helping
https://www.dropbox.com/s/81xap6m34negx3m/20160508_154845.jpg?dl=0
Pretentious packaging? Is the common person suppose to infer, an amino acid that is branched, is very good?
Anyway, what's so good about branched chain amino acid (BCAA)?
Originally posted by Flying grenade:Hi Ultima, i have some queries
Page 97 cs toh advanced guide
Btm of the page "C=O bond energy in CO2 is significantly stronger than average bond energies given in data booklet"
Is the reason that why not all C-H or C=O bonds are the same, because the C or O atom might be attached to another (different) atoms in different compounds?
Thanks for helping
Originally posted by Flying grenade:https://www.dropbox.com/s/81xap6m34negx3m/20160508_154845.jpg?dl=0
Pretentious packaging? Is the common person suppose to infer, an amino acid that is branched, is very good?
Anyway, what's so good about branched chain amino acid (BCAA)?
https://en.wikipedia.org/wiki/Branched-chain_amino_acid#Claims_in_Bodybuilding
May I ask a general qns? My school tutor claimed that for energy lvl diagram when the 3d and 4s orbital is filled, 3d orbital will have a higher energy than 4s orbital but when unfilled, the 4s orbital will have a higher energy than 3d orbital. Is that true?
Originally posted by MightyBiscuits:May I ask a general qns? My school tutor claimed that for energy lvl diagram when the 3d and 4s orbital is filled, 3d orbital will have a higher energy than 4s orbital but when unfilled, the 4s orbital will have a higher energy than 3d orbital. Is that true?
https://www.dropbox.com/s/fr20pd8kwayzf4f/Screenshot_2016-05-08-21-25-25-1.png?dl=0
Energy level of orbitals when unfilled : 3d > 4s
When filled , energy of 4s orbital > 3d
@mightybiscuits Looks like your teacher taught wrong. Or you typed wrongly. Or u copied wrongly. Or u misinterpreted. Regardless of the case, rectify the mistake, and make sure you internalise and learn the correct chemistry info. Cheers !
Hi ultima,
I read cs toh book page 108 and understood *why* O2(g) is a *better choice* than F2(g) as an oxidiser.
But i thought of comparing oxidising strength between F2(g) and O2(g)
I know F2(g) is the strongest oxidising agent of all known chemical compounds (or is it just the strongest, common oxidising agent?)
Question : how to determine oxidising power of O2? In the data booklet, there isn't any equation for O atom , e.g. O2 + 4e- -> 2O2- , unlike F, which has a eqn F2 + 2e- -> 2F- , with a given E°value.
Is oxidising power related/affected to electronegativity? Are there other factors?
2. Came across this "Why is F2 a stronger oxidising agent than Cl2 even though F2 has a less exothermic E.A than Cl2? "
https://www.quora.com/Why-is-F2-the-most-oxidising-agent-instead-of-Cl2-even-though-F2-has-less-electron-affinity-than-Cl2
But don't really understand fully
Originally posted by Flying grenade:Hi ultima,
I read cs toh book page 108 and understood *why* O2(g) is a *better choice* than F2(g) as an oxidiser.
But i thought of comparing oxidising strength between F2(g) and O2(g)
I know F2(g) is the strongest oxidising agent of all known chemical compounds (or is it just the strongest, common oxidising agent?)
Question : how to determine oxidising power of O2? In the data booklet, there isn't any equation for O atom , e.g. O2 + 4e- -> 2O2- , unlike F, which has a eqn F2 + 2e- -> 2F- , with a given E°value.
Is oxidising power related/affected to electronegativity? Are there other factors?
2. Came across this "Why is F2 a stronger oxidising agent than Cl2 even though F2 has a less exothermic E.A than Cl2? "
https://www.quora.com/Why-is-F2-the-most-oxidising-agent-instead-of-Cl2-even-though-F2-has-less-electron-affinity-than-Cl2
But don't really understand fully
I'll explain the following just once. For further discussion (eg. in case you still don't fully understand), go ask your school teacher or private tutor.
Oxidizing strength is primarily related to electronegativity, but secondarily to hydration enthalpy, because in the natural world, redox reactions occur mostly in the aqueous environments (ie. water being the solvent that brings the reactants together and allowing chemical reactions to occur), hence the redox potentials that are relevant are in the aqueous state.
Yes, F2 a stronger oxidizing agent than Cl2 even though F2 has a less exothermic EA compared to Cl2. First, understand why Cl2 has a more exothermic EA compared to F2 : it's because even though F is more electronegative than Cl, but the charge density of F- is too high due to small ionic radius, concordantly the inter-electron repulsions within the small F- ion are highly destabilizing. Consequently, the EA for F isnt as exothermic, as F- isn't as stable as might be imagined solely due to electronegativity (as would be the case with Cl to Cl-), as there is also a destabilizing (ie. endothermic) component to the EA process for F (but not for Cl), ie. the inter-electron repulsions of the high anionic charge density F- ion.
Next, if the EA of Cl is more exothermic compared to that of F, shouldn't Cl2 be a stronger oxidizing agent (ie. more positive reduction potential) compared to F2? Yet the Data Booklet clearly shows F2 having a more positive reduction potential compared to Cl2, and F2 is thus the stronger oxidizing agent. This is because as I mentioned earlier, we're interested in redox reactions occurring in the aqueous solvent or phase, and thus concordantly by Hess Law, reduction enthalpy = electron affinity enthalpy + hydration enthalpy ; and likewise oxidation enthalpy = ionization enthalpy + hydration enthalpy.
Because F- has a much higher anionic charge density compared to Cl-, it's hydration enthalpy is also that much more exothermic (ie. much stronger ion - permanent dipole interactions formed). And after Hess Law is applied, the overall reduction potential of F2 to F-, is still more positive compared to the reduction potential of Cl2 to Cl-, and thus in aqueous environments, F2 is still a much stronger oxidizing agent compared to Cl2.
I told you before : in the natural world, these redox reactions occur mostly in aqueous environments / solvents / phases. Do you think the highly unstable O2- ion is able to exist in aqueous environment? Of course not! It will kena immediately hydrolyzed to OH-, and (depending on pH) can be further protonated to H2O.
So for the oxidizing power of O2, look in the Data Booklet for the reduction potential of O2 to either OH- or H2O (depending on pH). (Ignore obscure & rare reduction products like peroxides, super oxides, ozonides, etc, unless otherwise specified by the question).
F- (aq) can exist in aqueous environment ?
Rephrase qn : is F- more stable than O2- ?
Is it cos O2- has dinegative charge so it's very unstable?
Polyatomic ions with dinegative charge e.g. SO42- , S2O32- , S4O62- , S2O82- , can exist* due to resonance stabilisation?
Update: Can exist in aqueous form*
O2- does exist, but not in aqueous form
Originally posted by Flying grenade:F- (aq) can exist in aqueous environment ?
Rephrase qn : is F- more stable than O2- ?
Is it cos O2- has dinegative charge so it's very unstable?
Polyatomic ions with dinegative charge e.g. SO42- , S2O32- , S4O62- , S2O82- , can exist* due to resonance stabilisation?
Update: Can exist in aqueous form*
O2- does exist, but not in aqueous form
Why is the d(x2-y2) and d(z2) at a higher energy level than the other three d orbitals again? The two aforementioned d orbitals lie on the axes or something??
Originally posted by Flying grenade:Why is the d(x2-y2) and d(z2) at a higher energy level than the other three d orbitals again? The two aforementioned d orbitals lie on the axes or something??
Originally posted by UltimaOnline:
Oi. There are hundreds of websites on the internet which explain (with diagrams too!) basic A level Chemistry concepts such as these. Don't be lazy.
I know repulsion
My school wrote this : *drew carbocation intermediate* carbocation formed is more substituted (2 alkyl groups). Alkyl groups are e- donating, thus dispersing positive charge on carbocation
Is this explanation incomplete/wrong, and/or cannot get full marks when Cambridge mark?
Need write this
To get full marks, you need to draw both mechanisms (or at the very least, both the carbocation intermediates) for both products, then specify which carbocation is the more stable carbocation (ie. benzylic carbocation > allylic carbocation > tertiary carbocation > secondary carbocation > primary carbocation), then explain "The more stable the intermediate, the lower the Ea required, hence the faster the rate of reaction, hence we get more of the product, which we label as the major product." ?
The plasma state of matter and blood plasma is diff plasma hor??
Originally posted by Flying grenade:The plasma state of matter and blood plasma is diff plasma hor??
A classmate of mine asked a qn in class in which the tcher was stumped and unsure how to answer : why electron shell closer to nucleus, has lower energy level?