Chemistryyy (3 Viewers)

[Shuuya]

Thnx

No worries

 

[drsabz101]

So for writing the net ionoc equation for oxygen + calcium, I got everything right except at the end of the equation on the products side it is Ca2+(aq) + O2-(s)

Why is it O^2- and not just O2

 

[Shuuya]

The reaction is:

2Ca + O2 ---> 2CaO

So net ionic equation is:

Ca + O2 ---> 2Ca2+ + 2O2-

What was your original equation?

 

[leehuan]

I do not remember doing any of this in the metals topic, what syllabus point is this

 

[drsabz101]

ohh , I have been writing the half equations out and then adding them. Can u post what the half equations should look like?

 

[Shuuya]

I do not remember doing any of this in the metals topic, what syllabus point is this

I think we touched on some of this, but not in much detail

 

[leehuan]

I think we touched on some of this, but not in much detail

We did do metal displacement in prelim but not oxidation states. That was taught to us in PoM

 

[drsabz101]

I do not remember doing any of this in the metals topic, what syllabus point is this


Here is a pic of the dot point:

 

[leehuan]

I do not remember doing any of this in the metals topic, what syllabus point is this


Here is a pic of the dot point:
View attachment 32822

It just says "transfer of electrons" without any specific mention to oxidation states and the fact it is a redox reaction

 

[drsabz101]

I guess its good for practice anyways. People in the same yr as me know this stuff as well. Their school has already taught them all of this

 

[leehuan]

Either top school or weird teachers. No harm knowing extra stuff though

 

[Shuuya]

Either top school or weird teachers. No harm knowing extra stuff though

Our year 10 teacher went through redox reactions using the standard potentials table but no one knew what was going on

 

[leehuan]

Yr 10 is way too early to make sense out of it.

 

[drsabz101]

That's true . A top school . Not selective tho

 

[blackbird_14]

That's true . A top school . Not selective tho

Figures. Most people in (my) year 11 (class) when its first taught don't get it immediately, so it's great it looks like you've got your head wrapped around the concept

 

[drsabz101]

Can someone write out how the half equations for oxygen + calcium, should look like. Thankyou^^

 

[DatAtarLyfe]

Oxidation:
Ca ----> Ca2+ + 2e-
Or 2Ca -----> 2Ca2+ + 4e-

Reduction:
O2 + 4e- -----> 2O2-

If you dont know which one oxidises or reduces, use the periodic table. As i said yesterday, metals oxidise and non-metals reduce

 

[drsabz101]

So for oxygen wouldn't the reduction equation just be:

O2+ + 2e- -> O2-

Why do u multiply everything again by 2

 

[leehuan]

Combustion of calcium metal:

2 Ca(s) + O2(g) -> 2 CaO(s)
with oxidation states:
(0) (0) -> (Ca 2+), (O 2-)

Hence, oxidation:
2 Ca(s) -> 2 Ca(2+) + 4 electrons
Because we write in simplest mole ratios:
Ca(s) -> Ca(2+) + 2 electrons

Reduction
O2(g) + 4 electrons -> 2 O(2-)

Note that in the case of oxygen, because O2 is a diatomic gas element molecule we can't dismantle that apart in our reduction half-equation.

The oxidation state of the oxide ion is also specifically 2-. This can be easily inferred from the periodic table. (If we had fluorine being reduced into the fluoride ion then the oxidation state of the fluoride ion is 1-.)

 

[drsabz101]

Why does oxygen gain 4 electrons though (sorry I still don't get it)