Adding salt to water does not decrease the time needed to reach boiling point; rather, it raises the boiling point of water, resulting in a longer time to boil. The ebullioscopic constant (Kb) for water indicates that adding salt increases the boiling point by a negligible amount—approximately 0.25°C for 0.5 moles of salt per liter. While cooking in saltwater can enhance flavor and prevent sticking, it does not significantly reduce cooking time. Empirical evidence suggests that the time to boil is longer with salt added, contradicting common cooking myths.
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It's nice to see that you are willing to explore the scientific method with her. Many adults are not so willing and go down the "everybody knows" route, which is counter-productive with kids. Kudos!kwinb said:just helped my niece test her hypothesis that salt added to water would decrease the time needed to reach boiling (100 C) using a candy thermometer
she used the 2 cups of water and did 3 tests each with 0, 1, 2, 3, and 4 tablespoons of salt
pot was identical, and was cooled to same starting temperature each time
she let the salt dissolve first, before initiating boiling. She found that the time to boiling point was nearly identical for 0 and 1 tablespoons, but the time to boiling decreased for each of the next sets of tests by about 1 to 1.5 minutes.
She is full of questions, and possible next steps
It is so nice to see her excited about it