Some multiple choice questions...

So the first one assign oxidation states to the metal before and after although if you give them all a cursory glance you should be able to spot the one with an increase in oxidation state pretty quickly. The second one is just a remembering metal ion tests one- two metal make the same coloured participate (white) with ammonia and you differentiate between them by adding excess ammonia and one redissolves (I remember this from edexcel c3). Third one I haven't done a2 yet but I think it's 2. Last one is a comparing increasing strength of id-id intermolecular forces as Mr increases vs hydrogen bonded in terms of strength.

One of the questions didnt attach:


For the first one its D but i dont really know why. The oxidation state of Mg = 2+ on both sides.

No idea what youre saying for the second one :/

I thought it was 2 too but the answer is B

Why is the last one not D - F is more electronegative than N right?

So a couple misunderstandings which is what they do with multiple choice, place feasible incorrect answers. Remember that the oxidation state of an element is 0 so Mg goes from 0 to +2 in the first one. For the last one, the greater mr making stronger instantaneous diope- induced dipole bonds is actually more significant than slightly stronger hydrogen bonds. For the second one, it should be in the textbook in the bit about ion tests.

Ohh yeah i forgot about that rule. For diatomic molecules like Cl2 is the oxidation state also 0?

Wait dont they both have permanent dipole? Do you mean the CH3NH2 has stronger van der waals as both have H bonding and permanent dipole?

Ohh yeah i forgot about that rule. For diatomic molecules like Cl2 is the oxidation state also 0?

Wait dont they both have permanent dipole? Do you mean the CH3NH2 has stronger van der waals as both have H bonding and permanent dipole?

Out of that list only methylamine has hydrogen bonding. Don't forget that hydrogen bonding not only only requires the presence of N,O,F, but it must be connected to an H. Fluoromethane does not have hydrogen bonding.

Hydrogen bonding is the strongest IM force, with the caveat that Van der Waals becomes stronger as molecules increase in weight. Obviously C12H26 has a higher boiling point than methylamine.

From strongest to weakest forces is it:

Ionic/covalent ---> H bonding ----> dipole-dipole ----> van der waals

It is not quite as straightforward as that as I was trying to point out with the C12H26 example. This has a much higher boiling point than smaller molecules with hydrogen bonding.

If the Mr is roughly the same, then you are right H bonding is stronger than dipole-dipole which is stronger than Van der Waals.

As Mr increases, VDWs becomes very significant.

Many covalent bonds are exceptionally strong and stronger than ionic bonds. Most molecular covalent elements and compounds have low boiling points not because their covalent bonds are weak, but because the intermolecular forces which we are breaking in melting or boiling them are weak.

Ah ok but generally speaking that order is correct?

Perfect.

so does CH3F just have van der waals and permanent dipole?

Yep. People always fall for the examiner's trick here. They see an 'F' and think 'hydrogen bonding' without realizing that there is no H connected to the F!

Permanent dipole is the most significant intermolecular force in this particular molecule.

The white precipitate (AgCl) dissolves in excess ammonia to produce a colourless solution.