[susan53]

Hi Peter,
You've got five questions here - always put them in separate threads with their own topic heading. This makes them much easier for other people to find if they're interested in the same thing. Also, to answer all your questions in one reply would take ages and result in a very long answer look how long this answer to just your first question is! Split the questions to make it easier for us.

Here's a reply to your first question :

All four sentences are grammatically correct. The use of the preposition in a sentence like this is optional. Each version stems from a different proposition, which either does or doesn't contain the preposition. It may be :


1a) You use a bottle opener to open a bottle. So : I need something to open this bottle.
1b) You open a bottle with a bottle opener - So : I need something to open this bottle with

2a) You use money to buy food. So : They gave us some money to buy food.
2b) You buy food with money. So : They gave us some money to buy food with.

It depends which underlying proposition the speaker has (unconsciously of course) in mind when s/he formulates the sentence. Another nice example of the fact that grammar is choice - the grammar you use is dependent on the meaning that you wish to express.

A caveat however. Proposition 2b is much less likely to be used (and therefore to be present in the mind of the speaker) than 2b. The version ...to buy food with therefore sounds unusual. This is not because it is impossible or ungrammatical, but because it is much less likely to be used. Language use is about frequency as well as about grammaticality.