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Kenneth Kang

Thurday, February 27, 1997


Molality and NaCl Solution's Boiling Point

Molality is proportional to the change in the boiling point of a pure solution versus a solution (T=Kmi, m is molality and i is the particles per a formula unit). Our investigation involved H2O and NaCl. We were supposed to determine how many dissolved particles came from the measured mass of NaCl. We found that i was .


Various methods are used to quantify the concentration of a solution. There is molarity and percent solutions. Molality is useful for predicting the change in boiling and freezing points for a given solvent. Once the constant K is found for the solvent, it is constant for all solutes. Our experiment used water (K = 0.512 C°/molal). We measured the mass of NaCl, volume of water, and the temperature. Using these values, one can find the i, the number of dissolved particles per formula unit, for NaCl.


  1. Add some quantity (200mL) of distilled water to a 250mL beaker.
  2. Measure the boiling point making sure to shield the thermometer from the steam with a piece of cardboard.
  3. Add a measured quantity (60g) of NaCl and stir to dissolve.
  4. Measure the boiling point.


  • Water - 200mL 0.2 kg
  • NaCl - 60g 1.027 mol
  • H2O Boiling - 100° C
  • H2O + NaCl Boiling - 106° C
  • T 6° C
  • I 2.283
  • Analysis

    Our errors included the measurement errors in temperature (to the nearest degree C) and procedural errors like measuring the water (nearest mL) and NaCl (0.01 g). This results in an error in i of 0.196. The remaining 0.086 difference from the real value can be accounted for by the error in determining exactly when the thing is boiling, and there is also the error induced by the evaporating water.


    Our results reaffirmed the theory that i is 2 for NaCl. This theory could be used to design better anti-freeze that will prevent overheating. However, the sedimentation and the evaporation of the water, leaving the salt must be resolved.