Is there safe chemicals for making voice pitch or bass?
Assuming that helium and sulfur hexafluoride (as shown in the video) will give you the correct sounding "pitch" and "base", it would be fine if done correctly and safely. 

Helium is incredibly inert and so will not cause any sort of toxicity. It is also a very light gas, so it will exit your lungs quickly. Just do not breath only helium, or for a long time or you could suffocate. Make sure to get lots of normal air.

Sulfur Hexafluoride is also rather unreactive, but more dangerous. This is because it is heavy and will tend to stay in your lungs. Only use it for a short period of time, or you can asphyxiate. While the same goes for helium, it tends to exit your lungs more easily.

The actual mechanism that causes them to work is based of how dense they are. It does not change the pitch, however. Instead, it changes something called timbre. This is basically the fact the helium allows sound to travel much faster through it, so it is a similar affect to playing a video at a faster speed. 

Sulfur hexafluoride does the exact same thing, except it is much denser and does not allow sound to travel through it very quickly. 

If you want to do this, be careful! You can suffocate, especially with sulfur hexafluoride.