This is an irregular verb. It follows the conjugation pattern of the verb parecer.
Present 1st Person: blanquezco
PresentPresente
La nieve blanquece las montañas en invierno.
The snow whitens the mountains in winter.
FutureFuturo
Este producto blanquecerá la ropa vieja.
This product will whiten the old clothes.
ConditionalCondicional
El sol blanquecería las cortinas poco a poco.
The sun would whiten the curtains little by little.