By chance & By the way – 2 for 1

By chance – Por acaso

I found your site by chance.
Eu achei o seu site por acaso.

Over at WR, they explain that ‘por acaso‘ has a few other meanings, such as ‘in fact’ and ‘as a matter of fact’. Learn more here.

By the way – A propósito

– You are leaving, right?
– Yeah, I am.
– Oh ok. Are you going to the city, by the way?

– Você está saindo, não está?
– Sim, estou.
– Ah tá. A propósito, você está indo à cidade?

Use ‘a propósito‘ when you wish to say “in addition, but of less importance”.