Mergulhar vs. molhar
While both mergulhar and molhar can correspond to the English verb "to dip", they describe different physical actions. Mergulhar focuses on the action of submerging or plunging something into a liquid, while molhar focuses on the result of making something wet or lightly touching the surface.
Mergulhar
B1This verb is related to dive or submerge. You use mergulhar when you put an object deep into a liquid or completely under the surface. It implies a sense of volume and immersion, such as dunking a cookie or plunging your hand underwater.
Eu gosto de mergulhar o biscoito no leite quente.
(I like to dip the biscuit in the hot milk.)
O pintor precisa mergulhar o pincel na tinta.
(The painter needs to dip the brush in the paint.)
Mergulhe os pratos na água com sabão para limpá-los.
(Dip the dishes in the soapy water to clean them.)
Ela mergulhou a mão no balde para pegar a esponja.
(She dipped her hand in the bucket to grab the sponge.)
Cuidado para não mergulhar a manga da camisa na sopa.
(Be careful not to dip your shirt sleeve in the soup.)
Molhar
A2The primary meaning of this verb is to wet. When used to mean dip, it suggests lightly touching a liquid, coating something in a sauce, or moistening an object. It focuses on contact and getting the object wet rather than deep immersion.
Vou molhar a batata frita no ketchup.
(I am going to dip the french fry in the ketchup.)
Ele molhou o dedo na água para ver a temperatura.
(He dipped his finger in the water to see the temperature.)
Gosto de molhar o pão no azeite.
(I like to dip the bread in olive oil.)
Ela apenas molhou os lábios na bebida.
(She just dipped her lips in the drink.)
Não esqueça de molhar o sushi no molho de soja.
(Don't forget to dip the sushi in the soy sauce.)
Summary
Use mergulhar when you are dunking or submerging something deep into a liquid volume (complete immersion). Use molhar when you are dipping food into sauces, testing a liquid's temperature, or simply getting an object wet (surface contact).