Question 18 from 2008 exam (1 Viewer)

[Dunnybrush]

Analyse the relationship between the position of elements in the Periodic Table, and the acid-base behaviour of their oxides.

4 mark question... and all i could get was that oxides get more acidic going from group 1 to group 7...

 

[tommykins]

回复: Question 18 from 2008 exam

I'll give you a brief outline, and you can write an answer and I'll critique it.

Left side = metals, metal oxides are basic in solution and accept protons.
Right side = non-metals, non-metal oxides are acidic in solution, donate protons.
Middle = amphiprotic oxides which can act as a base or acid in solution.
Refer to the effect of acidity/basicity as you go down the periodic table.

provide formulas if you wish, though i don't think it is necessary

 

[minijumbuk]

Which exam is this?

 

[Dunnybrush]

Which exam is this?

Err 2008 hsc chem exam? I thought that was a given

Left side = metals, metal oxides are basic in solution and accept protons.
Right side = non-metals, non-metal oxides are acidic in solution, donate protons.
Middle = amphiprotic oxides which can act as a base or acid in solution.
Refer to the effect of acidity/basicity as you go down the periodic table.

provide formulas if you wish, though i don't think it is necessary

Actually it was the acidity and basicity going down the periodic table going down i was wondering about... Would it be the higher up the group it is the more acidic/basic it is?

 

[tommykins]

回复: Re: Question 18 from 2008 exam

Lol how can it be the 2008 exam when we haven't even done our exam?

And I'm not sure about going up/down the periodic table, i'm not too worried about this dot point cause you can't say that much on it.

try google or something.

 

[minijumbuk]

Re: 回复: Re: Question 18 from 2008 exam

lol that's why I asked what exam is this from... I don't like this question at all.

Why would they allocate 4 marks on this question? There's not so many things to talk about =O

And dude...Did you mean your school trial or something?

 

[henry08]

Re: 回复: Re: Question 18 from 2008 exam

I think this may be the Independet trial.

Lol maybe it is the 2008 exam and the Op is an informant helping us out.

 

[appletooth]

Actually it was the acidity and basicity going down the periodic table going down i was wondering about... Would it be the higher up the group it is the more acidic/basic it is?

From memory, I think the more metallic an element is, the more basic its oxide. And elements get more metallic going down groups. Therefore, the going down a group, the oxides of elements should get more basic. Same theory applies for acidic oxides.

I'd also mention the fact that the elements of group VIII (noble gases) don't form oxides, too.

 

[tommykins]

回复: Re: Question 18 from 2008 exam

then i think its metal, middle area, and non-metal oxides that need to be referred with equations giving the 4th mark.

 

[Dunnybrush]

Woah yeh i just read what i wrote... My bad sorry minijumbuk!

It was the 2004 hsc exam! I think its quite obvious that im thinking about these exams to much now lol...

Soo higher up the group more acidic, lower down more basic relative within the group! It all makes sense now! Thankyou!

I just had a thought just now to check the marking guidlines and...

I'd also mention the fact that the elements of group VIII (noble gases) don't form oxides, too.

Thats apparantly wrong...
Marking guidlines say: "Very few candidates provided accurate, up-to-date chemistry as in the oxides of
some of the noble gases."

 

[danz90]

Re: 回复: Re: Question 18 from 2008 exam

Just remember, all metal oxides are basic in solution, all transition metal oxides (except ZnO, which is amphoteric) are basic also.
Al2O3 and BeO are also amphoteric.

All non-metallic oxides (ie right hand side of periodic table) are acidic in solution. The inert gases do not produce acidic OR basic oxides.. except for Xeon, XeO3 is an acidic oxide.

Not sure about the lanthanides and actinides, though.

Just one question:

What is the difference between the meaning of AMPHOTERIC and AMPHIPROTIC?

I always thought they essentially mean the same thing.. that substances can react both as bases and acids, but I thought that amphiprotic was a bit more specific in saying that an amphiprotic substance can behave as both a proton acceptor and donor.

 

[Dunnybrush]

Amphiprotic means it likes water im pretty sure...

Amphoteric is the acid or the base.. the really annoying one if i remember well enough from six months ago or whenever it was i was meant to learnt it...

 

[Dunnybrush]

Wait forget that as well that, what i said was wrong (bad day today for me)

But yahoo answers seems to know what they are talking about http://answers.yahoo.com/question/index?qid=20080310220643AAVyPyh

 

[crammy90]

what makes an element more metallic?
i.e. what makes the element Sodium more metallic than lithium and potassium more metallic than sodium?
and how does this affect their oxide's nature?

 

[danz90]

what makes an element more metallic?
i.e. what makes the element Sodium more metallic than lithium and potassium more metallic than sodium?
and how does this affect their oxide's nature?

Perhaps the mobility of delocalised electrons? This could be explained by the lower ionisation energy for elements as you go down the periodic table.. ie Group I metals become more 'metallic' and reactive as you go down the group.

However... this isn't part of the HSC syllabus, and i've never seen such a question in past HSC papers.

 

[appletooth]

No, it's not in the HSC course. I think we did this in year 11 - when we were learning something to do with trends in the periodic table?

Anyway:

"Down a group, the metallic character increases, due to the lesser attraction from the nucleus to the valence electrons (in turn due to the atomic radius), thereby allowing easier loss of the outer electrons or protons."

Source: http://en.wikipedia.org/wiki/Periodic_trends#Metallic_character

 

[crammy90]

ok yeh i get that thanks heaps
so metallic character is just their ability to loose electrons i.e. the less electronegative the higher the metallic character??? or is it just their ability to hold onto their own electrons, not necessarily attract other atoms'

EDIT:
metallic character is just their ability to have characteristics of metals i.e.
a) conduct electricity and heat (dont know why)
b) solid at room temp (except heavy metal mercury)

Non-metals have least metallic character (dont exhibit those characteristics that define a metal): so i guess that means they:
a) dont conduct electricity or heat (i dont know why they dont conduct?)
b) gases at room temp/liquids

i thinkt thats right
any1 know why metals conduct and non-metals dont and why they are different states at room temp?