Which separation method removes water to leave salt behind when treating seawater?

Which separation method removes water to leave salt behind when treating seawater?

• A. Filtration
• B. Distillation
• C. Centrifugation
• D. Evaporation

Answer: (D)

Removing water from a saltwater solution by evaporation relies on what happens to a dissolved substance when the solvent is removed. Salt is dissolved in seawater, so it doesn’t vaporize with the water. If you heat the mixture, the water molecules escape as vapor and leave the dissolved salt behind. As more water leaves, the remaining solution becomes concentrated until the salt can be recovered as a solid. This is the simplest way to separate a dissolved solid from a liquid. Filtration wouldn’t work here because the salt isn’t present as undissolved particles to filter out. Centrifugation relies on differences in density of solid parts, which isn’t the case for dissolved ions. Distillation also removes water, but it’s more involved since it’s aimed at collecting the water as a separate liquid; evaporation achieves the same end—water exits, salt stays behind—in a straightforward way.

Removing water from a saltwater solution by evaporation relies on what happens to a dissolved substance when the solvent is removed. Salt is dissolved in seawater, so it doesn’t vaporize with the water. If you heat the mixture, the water molecules escape as vapor and leave the dissolved salt behind. As more water leaves, the remaining solution becomes concentrated until the salt can be recovered as a solid. This is the simplest way to separate a dissolved solid from a liquid.

Filtration wouldn’t work here because the salt isn’t present as undissolved particles to filter out. Centrifugation relies on differences in density of solid parts, which isn’t the case for dissolved ions. Distillation also removes water, but it’s more involved since it’s aimed at collecting the water as a separate liquid; evaporation achieves the same end—water exits, salt stays behind—in a straightforward way.