会う and 遭う: meeting people and encountering trouble
Distinguish two spellings of あう for meeting and adverse encounters, comparing に and と for people with に for events.
Meet a person
駅で友達に会いました。 says that someone met a friend at the station. 会う, read あう, describes meeting a person, while で marks the location.
先生と会って、進路について相談しました。 says that someone met the teacher and discussed future plans. と marks the person met, and the discussion also took place.
Planned and chance meetings
明日、担当者に会います。 says that the speaker will meet the person in charge tomorrow. 会う alone does not fully determine whether a meeting is planned or by chance.
道で偶然、昔の友達に会いました。 says that someone unexpectedly met an old friend on the street. 偶然 specifies the chance encounter without requiring the spelling 遭う.
Encounter something adverse
旅行中に盗難に遭いました。 says that someone suffered a theft while traveling. 遭う is used for adverse events, with に marking the event.
ひどい目に遭いました。 describes having a very unpleasant experience. Interpret the expression as a whole rather than reading 目 only as a physical eye.
Must 遭う be used for unexpectedly meeting a friend?
Show the answer and why
No. 偶然友達に会いました is possible. 遭う normally concerns adverse experiences; chance alone does not determine the spelling.