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acids & bases

would it be correct to say that:

alkalis dissociate in acids AND water
bases dissociate in acids only
Original post by medhelp
would it be correct to say that:

alkalis dissociate in acids AND water
bases dissociate in acids only


no, they both react with acids.
Alkalis are soluble bases. Bases react with acids to neutralise them
Reply 3
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medhelp
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Original post by charco
no, they both react with acids.


so why do we make the distinction of alkalis being soluble

surely to react with an acid they have to dissociate in the acid then the ions react?
Original post by medhelp
so why do we make the distinction of alkalis being soluble

surely to react with an acid they have to dissociate in the acid then the ions react?


Not so.

Metal oxides are classified as bases, but most are totally insoluble. Copper(II) oxide reacts with acids forming salts and water, but it is insoluble in water.

The distinction is pretty meaningless, but you can consider a soluble base to be an alkali.
Reply 5
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medhelp
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Original post by charco
Not so.

Metal oxides are classified as bases, but most are totally insoluble. Copper(II) oxide reacts with acids forming salts and water, but it is insoluble in water.

The distinction is pretty meaningless, but you can consider a soluble base to be an alkali.



could you help me with another question as well, please?


the answer is c - 3 but i don't get how, I keep getting either 1 or 5 as my answer?

Spoiler

(edited 6 years ago)
Reply 6
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alow
19
Original post by medhelp


method 1:

cobalt has 27 electrons
1s2 2s2 2p6 3s2 3p6 4s2 3d7
therefore cobalt 2+ is 3d5 which is a half filled shell so all 5 are unpaired?


There's your mistake.
To add to Alow's post, it is always the 4s electrons that are lost first ...
Reply 8
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medhelp
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Original post by charco
To add to Alow's post, it is always the 4s electrons that are lost first ...


why are 4s lost first, I thought 3d was a higher energy level?
Original post by medhelp
why are 4s lost first, I thought 3d was a higher energy level?


OK, the real reason why is complex and the domain of university level treatment of orbitals. (Alow can do the honours if he so chooses - I won't)

The "accepted A' level" reason is that the 4s and 3d levels are very close in energy, but the occupation of the 3d level lowers its energy wrt the occupied 4s level.

So, when filling up, the 4s fill before the 3d and when losing electrons the 4s are removed before the 3d.

Chromium, d5, and copper, d10, are however, exceptions as the 4s only singly occupies while the 3d is half-full and full respectively.

When you get the the second and third row TMs the whole thing is thrown into a cocked hat, so just consider yourself fortunate that you only have to deal with 1st row TMs.

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