Exams actually looking ok for me

.
But right now, I cannot possibly seem to find this piece of music stuck in my head, despite the fact that everyone knows it. I've googled search out anything and everything on mozart (I think it's him, but then again it doesn't look like Magic Flute or Don Giovanni or anything I found so maybe it's not) but don't know the name of the music so I can't find it.
It's that very dramatic, opera piece that plays all the time in commercials too! Really, everyone knows it and I'm so angry I can't remember. Never even memorized it for quizbowl, I should know the name but I don't!! Something like this:
*very high pitched strings/women sing, then gets lower (
high pitch,
low pitch*
ding DING ding ding
ding DING ding ding
ding DING ding dah dah DAAH dah
DUH DUH
ding DING ding ding
ding DING ding ding
ding DING ding dah dah DAAH dah
DUH DUH
I don't know the words to this, I am quite sure it's latin but maybe an outside shot at Italian, but it might have something like "sanctus" in it, then again if you recognize it by this point this would sound really stupid of me, but anything that helps, y'know.