What is the main idea of the passage?

Dissolved salt lowers water's freezing point, causing ice to melt and absorb energy so an ice bath can become colder. (The text connects freezing-point change, melting, energy absorption, and the colder brine; that full chain is the passage's central explanation.)

Why does the temperature fall after some of the ice begins to melt?

Melting draws thermal energy from the mixture and nearby material. (The second paragraph says melting requires energy and that this energy comes from the mixture and objects exchanging heat with it.)

In this passage, what is “brine”?

Water containing dissolved salt (The first paragraph says salt dissolves into ions and creates brine, so brine is the resulting saltwater solution.)

How did historic hand-cranked freezers use the ice-and-salt mixture?

They placed colder brine around a separate inner container. (The final paragraph states that an ice-and-salt bath surrounded a separate container and received heat from the mixture inside.)

Why Salt Makes an Ice Bath Colder: Level 4 Reading Comprehension Questions

A bowl containing only ice and liquid water tends toward a balance near water's normal freezing point. Add salt, and that balance changes. The salt dissolves into sodium and chloride ions, creating brine whose freezing point is lower than that of pure water. Liquid can therefore remain beside ice at a temperature below zero degrees Celsius.

Salt first needs a film of water in which to dissolve. As a result, some ice melts to make more brine. Melting requires energy because molecules in liquid water have more freedom of motion than molecules locked in ice. That energy comes from the mixture and anything exchanging heat with it, so the bath becomes colder. Salt does not act as a packet of cold; it changes which phase is favored, and the resulting melting absorbs thermal energy.

Concentration matters. More dissolved particles can lower the freezing point across a useful range, but the effect is not unlimited. Eventually no more salt dissolves, while incoming heat and melting ice keep changing the mixture. Hand-cranked freezers used this behavior by placing an ice-and-salt bath around a separate container. Heat moved from the inner mixture into the colder brine as the crank turned it. The device did not make winter from salt alone. It arranged dissolution, melting, and heat transfer so that an ice bath could settle at a colder equilibrium.

Comprehension questions