chemistry unit 2 aqa thread

Define electrolysis (2 marks)

-Separation of an ionic compound into its comprising elements
-Using electricity

You may be given copper carbonate - copper has a +2 charge and carbonate ion has a -2 charge, this is depicted on the reactivity series handout.

The Copper carbonate needs to be in a solution form in order for electrolysis to occur as ions can move
Metals are generally melted into molten form so that ions can move and a flow of charge can transpire

the positive ions form at the negative electrode
the negative ions - carbonate (-2) form at the positive

think like charges attract,

this is because the negative electrode wants to give the positive ion an electron so that it becomes the original Cu - copper metal from the copper ion by gaining 2 electrons. it becomes reduced.
the positive electrode wants to take away electrons from the negative ion, the negative ion becomes oxidised

at the negative electrode the metal will be produced if it is less reactive than hydrogen hydrogen will be produced if the metal is more reactive than hydrogen, you can see this by looking at the reactivity series

as copper is less reactive than hydrogen , copper is formed

the equations are easy to balance and complete, they will ask you to complete ___O^2- → O₂ + ____
it would need to be 2 O^2- this is beacuse there is 2 oxygens on the other side so there needs to be 2 oxygens on this side

on the right i would need to be e- to represent the electrons lost by the oxygen ion, the number would need to be "4e-" due to the fact that there are 2 electons needed to be lost by each oxygen oxygen ion so it becomes O, there are 2 Oxygens due to "2O^2-" which means that there are 4 electrons as 2x2 = 4

btw, with cryolite,

Cryolite is used in the electrolysis of aluminium because

-it reduces the melting point of aluminium
-meaning that less temperature is required to melt it so it is molten and the ions can move
-less energy required as less temperature is needed to melt aluminium
-reducing energy costs

if the electrodes are carbon just remember that carbon electrodes react with oxygen, if oxygen is being formed at an electrode that is fabricated with carbon then the oxygen will react with the carbon and it will form CO2 and the electrode will slowly vanish c;

Sorry, but can you please further explain the formula where you had the answer of 4e-.

Thanks

yeah i found that hard. are you ok with empirical formula or working out the highest theoretical mass gain of a substance?

ok.

so if something is + then it must gain an electron because electrons are negative 1+ (-1) = 0 , so it can become the original metal.

2H⁺ + 2e^- → H₂

think of it as
H⁺ + e^- → H

hydrogen ion which is positive plus an electron goes to normal hydrogen "H", but because they have given you "H₂ " instead which is 2 hydrogens you must balance the equation so that there is an equal amount of hydrogen on each side

H⁺ + e^- → H_{2 -} you cant just leave it like this as the ratio is unbalanced
1 : 2
so you need to put a 2 infront of the hydrogen ion so that it becomes

2H⁺ + e^- → H₂
2 : 2

but as each hydrogen ion gains one electron and you have now made it 2H⁺ so that there are now 2 hydrogen ions it means that 2 hydrogen ions take 2 electrons as one hydrogen ion takes one electron etc

so you make it

2H⁺ + 2e^- → H₂

yeah, i sat down at a desk and did all 10 past papers today, back to 2008 :> chaos. Every time the question comes up:

which of these questions cannot be answered by science alone, explain why

*tick the appropriate box*

why: it is based on opinion
it is an economic/ethical/environmental issue

also a question on why CO2 has a low boiling point:

-it is simple molecular
-there are weak intermolecular forces between the molecules
-little energy is required to break the bonds
-meaning that a low temperature will cause it to boil

or on the structure of graphite

-made of layers
-layers have weak bonds between them
-meaning that the layers can slide over each-other.
-meaning that graphite is soft or malleable.

or on diamond

-strongly covalently bonded to 4 other carbon atoms
-it is a giant covalent structure
-the structure is very rigid as there are no layers that can slide over each-other
-high melting point

or on thermosoftening / setting polymers

-thermosoftening polymers do not have crosslinks between the chains of monomers
-meaning that they can melt and the structure warps

or why to close the lid on chromatography

-prevent solvent from vaporating

or why not to use pen to mark the chromatography paper

-ink dissolves into solvent
-smudges and runs up the page
-affecting experiment

-

I literally am sat here staring at the 'salts,acids and base' revision page. I literally don't get it. Hope the 6 mark isn't on this or I'm dead

I think the unit 3 paper will be based upon the advantages and disadvantages of Hard water for the 6 mark

yeah, i sat down at a desk and did all 10 past papers today, back to 2008 :> chaos. Every time the question comes up:

which of these questions cannot be answered by science alone, explain why

*tick the appropriate box*

why: it is based on opinion
it is an economic/ethical/environmental issue

also a question on why CO2 has a low boiling point:

-it is simple molecular
-there are weak intermolecular forces between the molecules
-little energy is required to break the bonds
-meaning that a low temperature will cause it to boil

or on the structure of graphite

-made of layers
-layers have weak bonds between them
-meaning that the layers can slide over each-other.
-meaning that graphite is soft or malleable.

or on diamond

-strongly covalently bonded to 4 other carbon atoms
-it is a giant covalent structure
-the structure is very rigid as there are no layers that can slide over each-other
-high melting point

or on thermosoftening / setting polymers

-thermosoftening polymers do not have crosslinks between the chains of monomers
-meaning that they can melt and the structure warps

or why to close the lid on chromatography

-prevent solvent from vaporating

or why not to use pen to mark the chromatography paper

-ink dissolves into solvent
-smudges and runs up the page
-affecting experiment

-

Hope so! There's easily enough to say about that:

Advantages
– Stronger teeth/bones
– May reduce risks of heart disease
– Some people say it tastes better

Disadvantages
- forms scale + explain how - this reduces efficiency of electrical appliances such as kettles
- forms soap scum + explain how - wastes soap

Anything else anyone can think of??

Can someone explain reacting mass equations for me? im finding it so difficult to understand

Hope so! There's easily enough to say about that:

Advantages
– Stronger teeth/bones
– May reduce risks of heart disease
– Some people say it tastes better

Disadvantages
- forms scale + explain how - this reduces efficiency of electrical appliances such as kettles
- forms soap scum + explain how - wastes soap

Anything else anyone can think of??

Thank you so much for that and good luck for tomorrow.

This is super helpful!! Thanks

also a question on why CO2 has a low boiling point:

-it is simple molecular
-there are weak intermolecular forces between the molecules
-little energy is required to break the bonds
-meaning that a low temperature will cause it to boil


-

does anyone have any easy tips to remember how to make salts? I can remember that most chlorides, sulfates and nitrates are soluble, and most oxides and hydroxides are insoluble. But can someone help with the ways you make soluble and insoluble salts? e.g. precipitation, using alkalis, using metals