Chemistry: Post your doubts here!

[Namehere]

Can anyone explain me if fluoromethane (CH3F) can hydrogen bond with water (H2O)? Here is my thinking... Water can form a hydrogen bond simply because it has a hydrogen attached to an oxygen, but this has to come into contact with a lone pair from a second electronegative atom, in this case F in fluromethane. So, in theory, shouldn´t there be a hydrogen bond? Though, CH3F is insoluble in H2O...

 

[Namehere]

Can anyone explain me if fluoromethane (CH3F) can hydrogen bond with water (H2O)? Here is my thinking... Water can form a hydrogen bond simply because it has a hydrogen attached to an oxygen, but this has to come into contact with a lone pair from a second electronegative atom, in this case F in fluromethane. So, in theory, shouldn´t there be a hydrogen bond? Though, CH3F is insoluble in H2O...

And if the cause that it doesn´t dissolve in water is because CH3F is a gas and you have to decrease the pressure blablabla... would CH3F dissolve due to hydrogen bonding with water if it were a liquid at rtp?

 

[AnujaK]

Hi I'm just in the AS so I havnt solved A2 papers yet. Sorry :/ I'll see if I can get some of my friends to send me their papers though

When are u gonna do the same for A2 papers!it would be awesome if u take the same initiative for A2 soon,cuz we have papers next week!As students gonna get a great help from your work!

 

[A star]

And if the cause that it doesn´t dissolve in water is because CH3F is a gas and you have to decrease the pressure blablabla... would CH3F dissolve due to hydrogen bonding with water if it were a liquid at rtp?

isnt hte hydrogen suppose to be directly attached to NOF ?

 

[Namehere]

isnt hte hydrogen suppose to be directly attached to NOF ?

Yep, it is in the water. You need to have a hydrogen attached to O,N or F which comes into close proximity to another electronegative atom with a lone pair, as is the case of CH3F and H2O. Am i right? Anyone knows if there is H bond there? And why is it insoluble in H2O?

 

[A star]

a complex ion defination is " a central TRANSITION metal ion surrounded by ions or molecules called ligands" do we have too add transition or only metal ion?

 

[Farez]

Yep, it is in the water. You need to have a hydrogen attached to O,N or F which comes into close proximity to another electronegative atom with a lone pair, as is the case of CH3F and H2O. Am i right? Anyone knows if there is H bond there? And why is it insoluble in H2O?

In order for a halogenoalkane to dissolve in water you have to break attractions between the halogenoalkane molecules (van der Waals dispersion and dipole-dipole interactions) and break the hydrogen bonds between water molecules. Both of these cost energy. Energy is released when new attractions are set up between the halogenoalkane and the water molecules. These will only be dispersion forces and dipole-dipole interactions. These aren't as strong as the original hydrogen bonds in the water, and so not as much energy is released as was used to separate the water molecules.

CH3F, or any other flourine containing hydrocarbons, don't form hydrogen bonds with water. The reason behind that is beyond our syllabus and they won't ask a question on it unless they give appropriate information.

 

[Namehere]

In order for a halogenoalkane to dissolve in water you have to break attractions between the halogenoalkane molecules (van der Waals dispersion and dipole-dipole interactions) and break the hydrogen bonds between water molecules. Both of these cost energy. Energy is released when new attractions are set up between the halogenoalkane and the water molecules. These will only be dispersion forces and dipole-dipole interactions. These aren't as strong as the original hydrogen bonds in the water, and so not as much energy is released as was used to separate the water molecules.

CH3F, or any other flourine containing hydrocarbons, don't form hydrogen bonds with water. The reason behind that is beyond our syllabus and they won't ask a question on it unless they give appropriate information.

Well, I´ve researched and apparently there are hydrogen bonds between CH3F and H2O molecules... So how do you get to know that "CH3F, or any other flourine containing hydrocarbons, don't form hydrogen bonds with water" ?

Here is one of the sites it does say it forms H-bonds: http://pubs.acs.org/doi/abs/10.1021/jp308533b

In case this is asked in an exam, should I say CH3F does not form H-bonds WITH H2O? (since obv they don´t form between CH3F molecules...)

 

[unique111]

Somebody help!
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_43.pdf

Question 7c i

 

[Namehere]

Somebody help!
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_43.pdf

Question 7c i

You need to take into account the 79Br, 81Br, 35Cl and 37Cl isotopes, together with propene. If you add the Mr of propene with an isotope of Br and an isotope of Cl you get the answers.

 

[itallion stallion]

You need to take into account the 79Br, 81Br, 35Cl and 37Cl isotopes, together with propene. If you add the Mr of propene with an isotope of Br and an isotope of Cl you get the answers.

Can u plz clear my confusion stated on the previous page?thanks!

 

[unique111]

You need to take into account the 79Br, 81Br, 35Cl and 37Cl isotopes, together with propene. If you add the Mr of propene with an isotope of Br and an isotope of Cl you get the answers.

Thanks! Laina

 

[Namehere]

Can someone clear my confusion,when we have to calculate solubility of Ag2CO3 we divide the Ksp by 4'and take the cube root.now if we have to calculate solubility of Al2O3,by which no are,we gonna divide the Ksp with and which root are we gonna take!

For Ag2CO3 the solubility is just the cube root of the Ksp, nothing divided by 4, I think... For Al2O3 u take the fifth root, but they wouldn´t ask that, I think... WRONG

Ag2CO3 --> 2Ag + CO3 2-, Ksp = [Ag+] [CO3 2-], let conc (solubility) of Ag2CO3 = x

Therefore, (2x)^2 (x) = Ksp
4x^3 = Ksp
x = cube root (Ksp/4)

 

[Farez]

Well, I´ve researched and apparently there are hydrogen bonds between CH3F and H2O molecules... So how do you get to know that "CH3F, or any other flourine containing hydrocarbons, don't form hydrogen bonds with water" ?

Here is one of the sites it does say it forms H-bonds: http://pubs.acs.org/doi/abs/10.1021/jp308533b

In case this is asked in an exam, should I say CH3F does not form H-bonds WITH H2O? (since obv they don´t form between CH3F molecules...)

Flourocarbons are hydrophobic.

http://en.wikipedia.org/wiki/Fluorine

"Also, adding fluorine to organics increases their lipophilicity (ability to dissolve in fats) because the carbon–fluorine bond is even more hydrophobic than the carbon–hydrogen bond."

http://en.wikipedia.org/wiki/Fluorocarbon

"They have very low solubility in water, and water has a very low solubility in them (on the order of 10 ppm)"

"As a result, fluorocarbons have low intermolecular attractive forces and are lipophobic in addition to being hydrophobic/non-polar."

http://en.wikipedia.org/wiki/Organofluorine_chemistry

"Fluorine has the highest electronegativity of all elements: 3.98.[1] This causes the high dipole moment of C-F bond (1.41 D[1]).

Fluorine has the lowest polarizability of all atoms: 0.56 10−24 cm3.[1] This causes very weak dispersion forces between polyfluorinated molecules and is the reason for the often-observed boiling point reduction on fluorination as well as for the simultaneous hydrophobicity and lipophobicity of polyfluorinated compounds whereas other perhalogenated compounds are more lipophilic."

This obviously means they are insoluble in water, and that they don't form hydrogen bonds.

This is why they are used in sorbents to absorb oil from oil spills, and not the water (page 137 of the application booklet).

 

[LeoMessi]

Have you read the chapter on partition coefficients? This page does a great job in explaining the concept and how to do the calculations. http://www.chemguide.co.uk/CIE/section112/learningf.html

Read that page and try to figure out how to solve the question yourself. It's mostly math anyway.



No need to memorize colours of complexes, other than Cu2+ complexes, and iron (ii)/(iii) ones. Make sure you know the reason behind the colours as that is a very common question.

As for your second question, it's rather subjective. The colour of the Fe2+ solution really depends on the concentration of the ions. If it's dilute, the colour would be harder to notice than the very prominent purple of the KMnO4 solution. This is what I think to make the most sense. I have no idea what the examiner had in mind lol.

Thanks alot!!!

 

[Namehere]

Flourocarbons are hydrophobic.

http://en.wikipedia.org/wiki/Fluorine

"Also, adding fluorine to organics increases their lipophilicity (ability to dissolve in fats) because the carbon–fluorine bond is even more hydrophobic than the carbon–hydrogen bond."

http://en.wikipedia.org/wiki/Fluorocarbon

"They have very low solubility in water, and water has a very low solubility in them (on the order of 10 ppm)"

"As a result, fluorocarbons have low intermolecular attractive forces and are lipophobic in addition to being hydrophobic/non-polar."

http://en.wikipedia.org/wiki/Organofluorine_chemistry

"Fluorine has the highest electronegativity of all elements: 3.98.[1] This causes the high dipole moment of C-F bond (1.41 D[1]).

Fluorine has the lowest polarizability of all atoms: 0.56 10−24 cm3.[1] This causes very weak dispersion forces between polyfluorinated molecules and is the reason for the often-observed boiling point reduction on fluorination as well as for the simultaneous hydrophobicity and lipophobicity of polyfluorinated compounds whereas other perhalogenated compounds are more lipophilic."

This obviously means they are insoluble in water, and that they don't form hydrogen bonds.

This is why they are used in sorbents to absorb oil from oil spills, and not the water (page 137 of the application booklet).

Ok, I need explanations... "the carbon–fluorine bond is even more hydrophobic than the carbon–hydrogen bond." "Fluorine has the highest electronegativity of all elements: 3.98.[1] This causes the high dipole moment of C-F bond" - Isn´t this contradictory? If the bond is polar, shouldn´t it be hydrophilic?

Plus, I still don´t get why it doesn´t form H-bonds with water. Can you explain me clearly why it doesn´t, please? I also don´t get why its hydrophobic, if you could explain that too..

Thank you sooo much!

 

[Farez]

Ok, I need explanations... "the carbon–fluorine bond is even more hydrophobic than the carbon–hydrogen bond." "Fluorine has the highest electronegativity of all elements: 3.98.[1] This causes the high dipole moment of C-F bond" - Isn´t this contradictory? If the bond is polar, shouldn´t it be hydrophilic?

Plus, I still don´t get why it doesn´t form H-bonds with water. Can you explain me clearly why it doesn´t, please? I also don´t get why its hydrophobic, if you could explain that too..

Thank you sooo much!

It feels contradictory to me as well, but this is what makes sense to me:

Fluorine has the lowest polarizability of all atoms. From this statement, we can say that the C-F bond isn't polarized enough to form the strong hydrogen bonds i.e. the δ- of the F isn't negative enough to form a strong hydrogen bond with the H's δ+.

It's hydrophobic because of the organic part - the CH3 group for example. And if the molecule has a lot of carbons, the hydrophobic property increases. So increasing carbon number will make it more insoluble.

 

[A star]

Ok, I need explanations... "the carbon–fluorine bond is even more hydrophobic than the carbon–hydrogen bond." "Fluorine has the highest electronegativity of all elements: 3.98.[1] This causes the high dipole moment of C-F bond" - Isn´t this contradictory? If the bond is polar, shouldn´t it be hydrophilic?

Plus, I still don´t get why it doesn´t form H-bonds with water. Can you explain me clearly why it doesn´t, please? I also don´t get why its hydrophobic, if you could explain that too..

Thank you sooo much!

look here is the deal flourine has a different chemistry i have a feeling that its explaination lies in concepts we avent studied yet so its bettter 2 days before the exam to leave it then ask your respective sir teacher about it

 

[hope4thebest]

Why amides give pH=7 while amines are basic in nature? Logic?

 

[A star]

Why amides give pH=7 while amines are basic in nature? Logic?

they are neutaral compounds, the nitrogen cannot use ts lone pair