HSC 2012-2015 Chemistry Marathon (archive) (1 Viewer)

[psyc1011]

re: HSC Chemistry Marathon Archive

Does the water molecule only have hydrogen bonding intermolecular forces or does it also have dipole dipole forces - some websites say it does and some say it doesn't so I'm a bit confused. I originally though water doesnt have dipole dipole forces because its a symmetrical molecule...

I read on the interwebs that hydrogen bonding is a specific version of dipole-dipole force. That is, hydrogen bonding is a dipole-dipole force but with interaction of specified atoms (H, F, O, N). Whereas, a normal dipole-dipole is associated with any atoms.

And water has a net dipole so there exists dipole-dipole forces (diagrams everywhere on the net.)

I might just read more on chem (extra general knowledge)... can anyone confirm this?

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

You don't need to know it so no point

 

[Study_like_a_nerd]

re: HSC Chemistry Marathon Archive

You don't need to know it so no point

Yes you do...
You don't pick and choose what they put in HSC

 

[Ekman]

re: HSC Chemistry Marathon Archive

You don't need to know it so no point

Yes you do...
You don't pick and choose what they put in HSC

Well I think what drsoccerball is trying to say is that it would highly improbable that the HSC will ask about hydrogen bonding or dipole-dipole forces directly. However, you will most definitely need to know these types of bonding in order to answer other questions.

 

[Study_like_a_nerd]

re: HSC Chemistry Marathon Archive

Well yeah.. thats why I asked it - it was part of a question - comparing the bonds between ethanol and water

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Well yeah.. thats why I asked it - it was part of a question - comparing the bonds between ethanol and water

Just mention polar vs non polar...

 

[Gabriel Moussa]

re: HSC Chemistry Marathon Archive

Just mention polar vs non polar...

But if it asked in relation to structure you'd need to mention the elecronegativity of water which gives it its polarity etc

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Just mention polar vs non polar...

You could also mention hydrogen bonds and/or dipole-dipole forces.

 

[psyc1011]

re: HSC Chemistry Marathon Archive

I read on the interwebs that hydrogen bonding is a specific version of dipole-dipole force. That is, hydrogen bonding is a dipole-dipole force but with interaction of specified atoms (H, F, O, N). Whereas, a normal dipole-dipole is associated with any atoms.

And water has a net dipole so there exists dipole-dipole forces (diagrams everywhere on the net.)

I might just read more on chem (extra general knowledge)... can anyone confirm this?

Is this right???

 

[Study_like_a_nerd]

re: HSC Chemistry Marathon Archive

Is this right???

I really think that water does not form dipole-dipole bonds and only forms hydrogen bonds because in dipole-dipole, the electronegativity is uneven, so the molecule is not symmetrical, whereas water is a symmetrical molecule so it wont form dipole dipole bonds... I'm not 100% sure about this but that's what I remember

 

[Librah]

re: HSC Chemistry Marathon Archive

Questions

1. What is electronegativity and what causes it

2. What are dipoles

3. How do lone pairs interact with positive charge

If ceebs answering these, yeah hydrogen bonding is essentially just very strong dipole-dipole forces, and they're slightly directional like covalent bonds, but still much weaker than covalent bonds.

 

[psyc1011]

re: HSC Chemistry Marathon Archive

I really think that water does not form dipole-dipole bonds and only forms hydrogen bonds because in dipole-dipole, the electronegativity is uneven, so the molecule is not symmetrical, whereas water is a symmetrical molecule so it wont form dipole dipole bonds... I'm not 100% sure about this but that's what I remember

Symmetricity of a molecule does not mean the molecule is non-polar (no net-dipole). In one part of your response, you are right about the asymmetrical electronegativities of a molecule but on the next part, you argue molecular symmetry (not the same) or possibly have misunderstood the electronegativity spreads for water.

Dipole-dipole arise when a partially positive part of a molecule nears a partially negative part of a molecule. These partially positive/negative parts are the result of differences in eletronegativity 'clouds' within the molecule.

"A hydrogen bond is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge. The hydrogen then has the partial positive charge." We can deduce that hydrogen bonds are a subset of dipole-dipole forces.

I hope that clears some stuff, and correct me if I'm wrong.

Another thing is that you shouldn't rely on memory due to it's incredible unreliability

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Quick question, what's the difference between amphiprotic and amphiteric?

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Quick question, what's the difference between amphiprotic and amphiteric?

Amphiprotic means it has the ability to both gain a proton (or hydrogen) or lose a proton. This means it can either act as an acid or a base.
Amphiteric is an oxide which acts as both an acid and a base.(If iirc)

 

[Study_like_a_nerd]

re: HSC Chemistry Marathon Archive

Symmetricity of a molecule does not mean the molecule is non-polar (no net-dipole). In one part of your response, you are right about the asymmetrical electronegativities of a molecule but on the next part, you argue molecular symmetry (not the same) or possibly have misunderstood the electronegativity spreads for water.

Dipole-dipole arise when a partially positive part of a molecule nears a partially negative part of a molecule. These partially positive/negative parts are the result of differences in eletronegativity 'clouds' within the molecule.

"A hydrogen bond is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge. The hydrogen then has the partial positive charge." We can deduce that hydrogen bonds are a subset of dipole-dipole forces.

I hope that clears some stuff, and correct me if I'm wrong.

Another thing is that you shouldn't rely on memory due to it's incredible unreliability

Hmm yeah I see thx!

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Really urgent question, what's a simple method/procedure to write when performing a titration?

 

[Ekman]

re: HSC Chemistry Marathon Archive

Amphiprotic means it has the ability to both gain a proton (or hydrogen) or lose a proton. This means it can either act as an acid or a base.
Amphiteric is an oxide which acts as both an acid and a base.(If iirc)

Its Amphoteric first of all. Also all amphoteric substances don't have to be oxides, amphiprotic substances such as Hydrogen Carbonate (HCO3-) are also amphoteric as well, because by definition, amphoteric substances are substances that can react with both acids and bases. They don't 'act' like an acid or base, rather they react with them

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Its Amphoteric first of all. Also all amphoteric substances don't have to be oxides, amphiprotic substances such as Hydrogen Carbonate (HCO3-) are also amphoteric as well, because by definition, amphoteric substances are substances that can react with both acids and bases. They don't 'act' like an acid or base, rather they react with them

So would would you define an Amphoteric substance and an Amphiprotic substance?

 

[Ekman]

re: HSC Chemistry Marathon Archive

So would would you define an Amphoteric substance and an Amphiprotic substance?

Its just:
Amphiprotic: Substances that can either donate or accept a 'proton'
Amphoteric: Substances that can react with both acids and bases.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Its just:
Amphiprotic: Substances that can either donate or accept a 'proton'
Amphoteric: Substances that can react with both acids and bases.

So basically that meaning of amphiprotic also applies for amphoteric and vice versa? Because if a substance reacts with an acid/base it's basically donating/accept a proton?