Intention

Performing nafl salaah with the intention of qadha for any salaah one may have missed

Q: Is it possible to make intention during nafl salaah that the nafl salaah be accepted for any qadha salaahs that one may have - specifically qadha salaahs that one may not be knowing of e.g. when ghusl after menstruation has been delayed or when a salaah may not have been performed in a state of wudhu unintentionally or one's ankles/hair may have been exposed, thus rendering salaah invalid?

Intention when making qadha of many salaahs

Q: I have qadha salaah from a certain year. I have read salaah in between but I'm not sure when my haiz fell during the year as well as which salaahs I read.

My question is, my intention for the qadha should be made from a specific date that my salaah became obligatory and each date so on till the current date, or should my intention be that, from the first of all the qadha I have right up until a number I assume I missed. 

Intention when making qadha salaah

Q: Regarding qadha salaah (missed prayers):

What is the full intention to make before one performs a qadha salaah (Note: the intention for ample salaah missed not just a single salaah). I am fearful that if my intention is incorrect my qadha salaah wont be accepted. Many books have the intention for only missing one prayer. 

To my knowledge the intention is "O Allah, I am reading the 1st fajr of those that I have missed" but I am unsure if it is correct.

Qadha for missed Salaahs

Q: Around ten years ago I had performed umrah. At the time I was negligent regarding my discharge and reading salaah with a fresh wudhu. I wish to repeat all of my salaah. What should my intention be before performing each salaah. It is 6 weeks of salaah.