FOR - TO (purpose or reason)

It is sometimes not clear what structure to use to talk about the use of an object (for cleaning) as opposed to the reason for which the object is used (to clean).

• Use or purpose of things/objects
  
  To explain the use of an object, what it is used for, we use for following by -ing
  • What is this sponge for? = For what purpose is it used?
    It is for cleaning the sink.
• Reason or purpose of actions
  
  To explain why we do something, the reason for which it is done,
  we use the infinitive (ex: to do)
• What do you use this sponge for? =  Why do you use it?
  I use it to clean the sink.
• Why did you turn on the radio?
  I turned on the radio to listen to the news.