Chem help- water topic.. (1 Viewer)

[VuongstER_boi]

Heyy ppls. I need some help with chem, any of you ppls could gimme some help? lol.

Alrights, i've been going throuhg some of my past chem quizes and can't understand why i got some of them wrong. My chem teacher is like not even qualified so like..I can't ask her-_-.

The question is : Identify the forces between the following molecules.

(b) oxygen and water:
My answer: Hydrogen Bonding. ( cos of the oxygen from oxygen(lol) and the hydrogenfrom water)
Correct Answer: Dispersion.(??)

(d) Hydrogen chloride and water:
My answer: Hydrogen Bonding ( the reason i think is cos the hydrogen in hcl can combine with the oxygen in water) .
Correct Answer: Dipole-Dipole. (??-_-)

 

[Martyno1]

The first one is definitely dispersion forces because two differently-natured molecules (O2 and H2O) have forces, and they can only be dispersion if they're of a different nature (I'm pretty sure).

Get it?

 

[VuongstER_boi]

hmm..so then, when can they be hydrogen bonds then? if they're both of the same nature?.... hmm... *thinks*. btw, thanks for posting =]

 

[undalay]

Oxygen or O2 is nonpolar. The forces between O2 molecules are dispersion forces.
Water or H2O is polar. The forces between H2O molecules are hydrogen bonds.

However since the O2 has no dipole ( and thus basically no charge) there is no electrostatic attraction between the slightly positive hydrogen and the oxygen in the O2 molecule, and thus the only intermolecular forces between them must be caused by the temporary dipoles: the disperson forces.

My Suggestion to you: revise over intermolecular forces, how and why they occur, and maybe read over electronegativities.

It's similar for HCL, only it's a bit dodgy because HCL basically instantly ionises and forms different substances with the water.

 

[sle3pe3bumz]

Oxygen or O2 is nonpolar. The forces between O2 molecules are dispersion forces.
Water or H2O is polar. The forces between H2O molecules are hydrogen bonds.

However since the O2 has no dipole ( and thus basically no charge) there is no electrostatic attraction between the slightly positive hydrogen and the oxygen in the O2 molecule, and thus the only intermolecular forces between them must be caused by the temporary dipoles: the disperson forces.

My Suggestion to you: revise over intermolecular forces, how and why they occur, and maybe read over electronegativities.

It's similar for HCL, only it's a bit dodgy because HCL basically instantly ionises and forms different substances with the water.

hm you know your stuff !

and I think the reason why HCl does not ionise is due to the fact that when you get get the electronegativities of hydrogen and chlorine it's equal to 0.96. To be an ionic compound, the bond different must be >1.55. Therefore it is a covalent molecular compound. This being said, I think that it can't ionise and therefore results in two polar molecules forming dipole-dipole forces between each other.

That's just my guess. I just realised I wrote than HCl ionises in my assignment. Dammit. ><"

 

[VuongstER_boi]

Oxygen or O2 is nonpolar. The forces between O2 molecules are dispersion forces.
Water or H2O is polar. The forces between H2O molecules are hydrogen bonds.

However since the O2 has no dipole ( and thus basically no charge) there is no electrostatic attraction between the slightly positive hydrogen and the oxygen in the O2 molecule, and thus the only intermolecular forces between them must be caused by the temporary dipoles: the disperson forces.

My Suggestion to you: revise over intermolecular forces, how and why they occur, and maybe read over electronegativities.

It's similar for HCL, only it's a bit dodgy because HCL basically instantly ionises and forms different substances with the water.

Ohh!!! I think I get it now. thanks Undalay!! Yea..cos for the first questions ( oxygen and water), oxygen doesn't have any dipole forces. So there's no way it can be attracted to they hydrogen of water. In order for hydrogen bonding to occur, there must be a dipole for both of the compounds. It's not just any compound containg nitrogen, oxyygen and fluorine that can under hydrogen bonding with a hydrogen from another compund. Same goes for the 2nd question. thanks!! Ohh yeah, thanks to all other ppls who helped as well !!

 

[Danger]

Hydrogen bonds only form between a hydogen atom and a highly electronegative atom (ie. nitrogen, oxygen and fluorine).