"c" in scented has nothing whatsoever to do with a schwa; it's a silent letter and a schwa is an unstressed vowel sound (like the "a" in "woman"). It could, however, be argued that both scented and vacuum have a schwa; the last vowel in scented is sometimes transcribed with a schwa and sometimes with a short "i" in IPA; the last syllable of vacuum would be transcribed with the IPA symbols "j + short "u" + schwa. This would be much easier to explain if I could use an IPA font . . . hope you get the idea.