The answer is yes.
Having said that, you probably is asking what is actually ‘mortal sin’.
Put simply, it is grave matter, committed wilfully. If one dies without repenting, then one is separated from God or falls from grace.
In reality and because of the definition of mortal sin itself, there is no knowing whether the sin one commits really fall into its category.
In Catholicism, even though we may commit mortal sin, usually it is mitigated in some ways before we go for Confession by our desire to confess it.
With so many mitigating factors, like ignorance, plus the mercy of God, we can never be certain that we will go to hell. Unlike saints who are in heaven, the Church will never declare that a person is in hell, simply because we do not know their hearts and the distance the mercy of God that covers them.