Impurities can significantly affect the boiling and melting points of substances. Here are some examples of how impurities can influence these properties, along with resources providing evidence for each example:
1. Presence of impurities in a solid increases its melting point:
Impurities can disrupt the regular arrangement of particles in a solid, making it more difficult for the solid to change into its liquid state. An example of this can be seen in the effect of impurities on the melting point of ice. Impure ice melts at a lower temperature than pure ice because the impurities interfere with the normal crystal lattice structure of ice. This is why salt can be used to lower the melting point of ice on sidewalks and streets during winter.
Resource: The Journal of Chemical Physics (1949) -
https://doi.org/10.1063/1.1748774
2. Presence of impurities in a liquid decreases its boiling point:
This is due to the phenomenon called "Raoult's Law," which states that the vapor pressure of a solution is proportional to the mole fraction of solvent. An example of this behavior can be seen with alcohol mixed with water. The boiling point of the mixture is less than the boiling point of water because the alcohol reduces the vapor pressure of the water, allowing it to boil at a lower temperature.
Resource: P. Atkins and J. de Paula, “Physical Chemistry,” W. H. Freeman and Company, 8th ed., 2006 -
https://www.amazon.com/Atkins-Physical-Chemistry-Peter-Paula/dp/0716787598
3. Presence of impurities in a liquid increases its boiling point:
This is called "boiling point elevation," which occurs when a nonvolatile solute is added to a solvent. The addition of a solute reduces the vapor pressure of the solvent, and as a result, the temperature at which the solvent boils is raised. For instance, adding salt to water increases its boiling point. This is why it's recommended to add salt to the water when cooking pasta, as it increases the boiling point of water, making the cooking process more effective.
Resource: Chapter 13.5 Colligative Properties of Solutions, Chemistry 2e, OpenStax -
https://openstax.org/books/chemistry-2e/pages/13-5-colligative-properties-of-solutions
In conclusion, the presence of impurities can either increase or decrease the boiling or melting points of substances, depending on the nature of the impurities, their concentration, and the substance being considered. Different factors, such as vapor pressure changes, interference in crystal lattice structures, and solute molecule interactions, can all contribute to these changes in boiling or melting points.
what impurties affect boling or melitng point with what substances
Give me evidence with resources
1 answer
1 answer