If you say my name, I will no longer exist. What am I?

These types of puzzles are known as charades. What you have to do is find two words that are referred to in the first stanza and the second stanza and put them together to form the third word in the third stanza.

Just for example, if my first refers to 'off' and my second refers to 'ice', then my whole will be office.

My first is present - future's past -
A time in which your lot is cast.

My second is my first of space
Defining people's present place.

My whole describes a lack of site -
A place without length, breadth, or height.

When I go in I might cause pain. I cause you to spit and ask you not to swallow. I can fill your hole. What am I?

What has many keys but can’t open a single lock?

I have an eye but still cannot see.

Who am I?

What is more useful when it is broken?

Two in a corner, one in a room, zero in a house, but one in a shelter. What is it?

My first is in chocolate but not in ham. My second is in cake and also in jam. My third at tea time is easily found. Altogether, this is a friend who is often around. What is it?

Can you find the missing piece of the Porsche?

I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. What am I?