Question

how is a mixture of salt and ice helpful in the making of ice cream​

Answer 1

ᴡʜᴇɴ ʏᴏᴜ ᴀᴅᴅ ᴊᴜsᴛ ɪᴄᴇ ᴛᴏ ᴛʜᴇ ɪᴄᴇ ᴄʀᴇᴀᴍ ᴍᴀᴋᴇʀ, ᴛʜᴇ ɪᴄᴇ ᴀʙsᴏʀʙs ʜᴇᴀᴛ ғʀᴏᴍ ᴛʜᴇ sᴜʀʀᴏᴜɴᴅɪɴɢ ᴀɴᴅ sᴛᴀʀᴛs ᴍᴇʟᴛɪɴɢ. ᴀᴛ 0ᴄ ᴇϙᴜɪʟɪʙʀɪᴜᴍ ɪs ʀᴇᴀᴄʜᴇᴅ ᴀɴᴅ ᴛʜᴇ ᴛᴇᴍᴘᴇʀᴀᴛᴜʀᴇ ᴄᴀɴɴᴏᴛ ɢᴏ ᴀɴʏ ʟᴏᴡᴇʀ.

ʙᴜᴛ ʙᴇᴄᴀᴜsᴇ ᴏғ ᴛʜᴇ ᴘʀᴇsᴇɴᴄᴇ ᴏғ sᴀʟᴛ ᴛʜɪs ᴍɪxᴛᴜʀᴇ ᴡɪʟʟ ʀᴇ-ғʀᴇᴇᴢᴇ ᴀᴛ ʟᴏᴡᴇʀ ᴛᴇᴍᴘᴇʀᴀᴛᴜʀᴇs ᴛʜᴀɴ 0ᴄ.

ʜᴏᴘᴇ ɪᴛ ʜᴇʟᴘs ʏᴏᴜ ᴍᴀᴛᴇ! :)

Answer 2

Answer:

In both cases, the answer is based on the fact that adding salt to an ice water mixture in equilibrium, lowers the freezing point (or melting point)  of the equilibrium. When you add just ice  to the ice cream maker, the ice absorbs heat from the surrounding and starts melting. At 0C  equilibrium is reached and the temperature cannot go any lower. This is not cold enough for making ice cream. When salt is added, the equilibrium will be reached, and kept at the lower temperatures required. But when salt comes into contact with the ice on the road some heat is released because of the solvation process. This melts the ice yielding once again an ice water equilibrium. But because of the presence of salt this mixture will re-freeze  at lower temperatures than 0C. In both  cases the lowering of the freezing point will depend on the concentration of salt in the mixture.  

Explanation: