Learn Portuguese (Portugal): A instituição de caridade ajudou todas quantas pediram uma doação. - The charity helped all the women who asked for a donation.

The phrase todos quantos is a relative pronoun of quantity meaning 'all those who' or 'as many as'. Here, it takes the feminine plural form todas quantas, which implies the unstated noun is feminine, like mulheres (women) or pessoas (people). It acts as a slightly more formal alternative to saying todas as mulheres que.

Could I use tudo quanto in this sentence instead?

No. The phrase tudo quanto is invariable and means 'everything that' or 'all that', referring to uncountable objects or abstract ideas. Because the charity is helping countable individuals, you must use the plural, variable form todos quantos, which shifts to todas quantas to match the gender of the people involved.

Why isn't there a Portuguese word for 'for' after pediram?

The verb pedir translates directly to 'to ask for' or 'to request'. The English preposition 'for' is already built into the verb's meaning, so it connects directly to the object being requested (uma doação) without needing an extra preposition like por.

What dictates the conjugation of the verb pediram here?

The relative pronoun quantas acts as the subject of the relative clause. Since it is a third-person plural pronoun referring to the women, the verb must match it, resulting in the plural conjugation pediram.