Most of the time during the day I have white coating on my tongue unless I clean it by brushing it with tooth powder. I'm not sure when I do wudu if this coating is a barrier and is stopping the water to touch the tongue. Even if i do brush some of it off there is still some left at the back of the tongue which is hard for me to brush, as it makes me feel like I want to vomit. Do I need to brush the tongue everytime I do wudu?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The view that we adopt here in Islamweb is that rinsing the mouth and nose is a Sunnah (recommended).

Even according to the view that this is an obligation, the presence of the coating you mentioned on the tongue or on other parts of the mouth does not affect the validity of rinsing the mouth, as this is achieved by the slightest movement of water in the mouth, even according to those who are of the view that this is an obligation, namely the Hanbali School. The Hanbali scholar Al-Buhooti said: “The obligation of rinsing the mouth is achieved by the slightest movement of water around inside the mouth.” [End of quote]

Based on this, you should know that just putting the water in the mouth and moving it around is sufficient even according to those who are of the view that rinsing the mouth is an obligation. Therefore, you should not burden yourself with what you mentioned in the question whether at the front of your tongue or at the back of it, or in any part of your mouth.

Allaah Knows best.