Dear Gabi,

Karpas is done with a vegetable dipped into either vinegar or salt water. (Shulchan Aruch Orach Chaim 473:6). The unusual dipping before the meal is to encourage children to ask questions.

There are many customs concerning which vegetables to use. Some use parsley, others use onions, radishes, potatoes or celery. Other vegetables can also be used but should have the Brachah of Borei Peri ha'Adamah. Types of Maror should not be used.

Concerning the dipping, the Shulchan Aruch mentions vinegar. The Mishnah Brurah 473:54 adds that wine and salt water is also permitted, but Charoses should not be used. Less than an olive-size is preferable.

The vegetable need not be totally submerged in the liquid. Even if the hand will not come in contact with the liquid, washing hands is required. However, according to the Mishnah Brurah using a spoon or fork with a wetted food, which is not normally eaten by hand, does not require washing the hands before its eating (Mishnah Brurah 158:19,21). Such vegetables should be held by hand. (All actual Halachah questions should be directed to your Rabbi.)

All the best,

Reuven Weiner