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Add 1.5g potassium nitrate and 4.5g water into 20% potassium nitrate solution, and the solute mass fraction of the solution obtained after dissolution is greater than or less than 20%?

Solution:

This problem can be equivalent to mixing 1.5g potassium nitrate and 4.5g water into a solution, and then mixing with 20% solution.

1.5g of potassium nitrate and 4.5g of water:1.5/(1.5+4.5) *100% = 25% >: 20%.

Therefore, the mass fraction of the mixed solution is more than 20%.