Many people add salt to a pan of water when they are cooking, and disagree as to

Question

Many people add salt to a pan of water when they are cooking, and disagree as to whether the salt is only there for flavor or if it speeds up the cooking process. Which is correct? (In other words, how much salt would you need to add to significantly increase the temperature of the boiling water?)

Make the following assumptions to answer this question:

1.   We are heating one liter of water (approximately one quart), the density of water is 1.00 g/mL, the density of salt is 2.165 g/cm3, and 1 cm3 = 0.0676 Tbs.

2.   An increase in the boiling point of 5 °C (nearly 10 °F) would decrease cooking time significantly.

3.   The boiling point elevation constant for water is 0.5121 °C/m.

4.   Assume that the van’t Hoff factor, i, for NaCl is 1.85.

To help put this into perspective, 6 g of NaCl is equal to 1 tsp and a canister of Morton’s Salt contains 737 g of NaCl.

Explanation / Answer

Elevation in boiling Point = i(vont hoff factor) * Kb * molality

5 = 1.85 * 0.5121 * molality

molality =5.2776 m

Molality = Number of moles of solute/mass of solvent in Kg

Mass of solvent = Volume of solvent * Density of solvent

=> 1000 mL * 1 gm/mL

=> 1 kg

Number of moles of solute NaCl = 5.2776 moles

Molar mass of NaCl = 23 + 35.5 = 58.5 gm/mol

Mass of NaCl required = number of moles of NaCl * molar mass

=> 5.2776 mol * 58.5 gm/mol

=> 308.744 grams

Mass in terms of tsp = 308.744/6 = 51.457 tsp = 51.5 tsp

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