What is the mass of the solution when 1 pound of salt is dissolved in 20 pounds of water?

The dissolution of salt in water is basically a physical process and the law of conservation of mass which states that mass can neither be created nor destroyed applies. The mass of each component before dissolution will be same after dissolution.

When one pound of salt is dissolved in 20 pounds of water, the resulting solution will weigh 1+20 pounds.

mass of solution = mass of salt + mass of water

= 1+20

mass of solution = 21 pounds

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