Chapter 15.3, Problem 8RQ

Interpretation Introduction

Interpretation: The reason for salt to be added to water while cooking pasta other than the reason to make it tasty needs to be explained.

Concept introduction: Colligative properties are those which depend entirely upon the number of particles of the solute dissolved in a known volume of the solvent and not on the nature of the solute.

When solute is added to a solvent then boiling point of the solution is greater than the pure solvent

Answer to Problem 8RQ

Addition of salt increases the boiling point of the solution and hence pasta cooks better.

Explanation of Solution

Addition of non-volatile solute in water decreases the vapor pressure of the solution. Hence, it should be heated to a higher temperature so that its vapor pressure becomes equal to that of the atmospheric pressure ( $1atm$ ).

Since, addition of salt in water raises the boiling point of the solution salt water is hotter than pure water and pasta cooks better in less time.

Conclusion

Addition of salt increases the boiling point of the solution and hence pasta cooks better.