(Original post by Edwseymour)
Could anyone please give some guidance on the question 3 of the attached:
I don't know how to reason the products of reacting one solution with another. I am sure that we are not expected to have memorized these specific cases. I have the answers but cannot see how you arrive at them.
On question 9)
a) Can you tell that this is a neutralisation reaction because acid + base usually produces a salt.
As silicon is a metalloid, you would not be able to tell ordinarily if SiO2 is a covalent structure or ionic and is it only because CaO is ionic (Metal + Non Metal) that you can conclude SiO2 is covalently bonded?
b) i) I can tell it is Oxygen from the relative sizes of the atom on the diagram, but am very confused to try and identify which atom is Oxygen and which is Silicon from the bonding in the diagram.
I am happy with the rest of the question.
Can anyone please help?
For question (3), essentially what's going on is that someone is reacting 2 solutions together. These 2 solutions are both of water-soluble salts, so their ions dissociate (dissolve) in the water. When the solutions are mixed together, if a pair of ions that forms an insoluble salt mix, they will come together and form a solid salt, because that ion combination is insoluble in water. This happens throughout the solutions and as a result, a powdery solid precipitate is formed, leaving the ions that don't react in solution.
Now, to answer the question. You need to look at pairs and see if there are any ion combinations that may produce insoluble salts. One that's already done for you: barium chloride and sodium carbonate are mixed together. Here you need to know your solubility rules!
Most carbonates are insoluble, apart from sodium, potassium and ammonium carbonates (because all sodium, potassium and ammonium salts are soluble). But barium carbonate is insoluble, and so it forms a solid precipitate.
You just need to use the solubility rules (which you will need to memorise
) to see if any insoluble salts can be formed from the combinations of ions in the reacting mixture. If no insoluble salts are formed, then there is no reaction: the ions keep minding their own business, floating around the solution as disassociated ions.
For question 9: There are more types of neutralisation reaction than you meet at GCSE. CaO is a base and SiO2 is an acid, so they react in a neutralisation reaction. You are taught this when you do the blast furnace for iron extraction, and you just have to remember that it's a neutralisation reaction between an acid (SiO2) and a base (CaO), to form calcium silicate (and to get rid of the silicon dioxide impurities from the iron). You could work this out from the 'rule' that metal oxides are bases and non-metal* oxides are acids
. I remember learning that at GCSE.
SiO2 is covalently bonded
, I think you should just know that. Even if you don't, you could work it out because the diagram shows lines drawn between the atoms, and by convention, lines between atoms represent covalent bonds (a shared pair of electrons). Though this might not be the best thing to go by. Generally, metalloids + non-metals form covalent bonds
(for GCSE purposes).
Aside: Ionic bonds act in all directions around the ions (they are omnidirectional) as they are just electrostatic attractions between opposite charges, and these attractions can come from any direction. Fun fact: Silicon dioxide is one of the most common components of sand.
You can tell its oxygen because the light grey blobs only form 2 covalent bonds throughout, while elsewhere in the diagram you can see dark grey blobs forming 4 covalent bonds (they have emitted bonds at the ends of the diagram). This means the dark grey must be silicon, hence light grey must be oxygen.
*I'm pretty sure you generally class metalloids as non-metals at GCSE, but it may be different for your spec.