How do impurities affect the melting and boiling points of water?

Answer 1

What happens

When a substance is pure, its melting and boiling points obviously stay the same as there are no changes to the actual substance. When a substance is impure, it causes its melting and boiling points to change and lie within a certain range. Whether the melting point increases or decreases depends on the bonding of the substance and the impurities, which gets quite complicated. For example, pure water has a boiling point of 100 degrees Celsius while water with impurities with have a boiling point in range of 100 degrees. Many factors make this so.

Why does it happen

One is the basic fact that there are more particles so the heat energy takes longer to travel through the solution (this is, if you consider particle theory, kinetic energy.)

Another factor has to do with bonding and some other chemical properties. If you want to read about this other factor, read the paragraph below. Otherwise, just skip it.

To continue with the simple example of a salt and water solution salt, I will talk about intermolecular forces. These are forces between molecules in the solution (the forces between the sodium chloride molecules and the water molecules). Sodium and chlorine are bonded with ionic bonds in sodium chloride. In case you don't know what ionic bonding is, read the paragraph below, otherwise, skip the paragraph.

Ionic bonding is a type of bonding between mostly metals and non - metals and you need to have a solid grasp of atomic structure to be able to comprehend this. Usually, a metal will have one electron on its outer shell. A non-metal, however, has an outer shell that is missing one electron. Both atoms 'want' to have a full outer shell (it actually has to do with electrostatic forces but this is a nice way to think of it). In order for both atoms, the metal one and the non-metal one to have a full outer shell, the metal atom loses its one electron on its outer shell and gives it to the non-metal, which now gains one electron on its outer shell to give it a full outer shell. Because the metal has lost an electron, it has now lost one unit of charge and has become positive, as it now has more protons than electrons, and the non-metal has gained one electron to become negatively charged. Any atom that has an imbalance of protons and electrons and its electric charge is therefore not balanced, is called an ion and this is called ionic bonding. The water molecule is covalently bonded. It has a hydrogen bond and this is because of electrostatic forces; oxygen has a chemical property called electronegativity, which sounds hard to understand but actually isn't. All it means is that oxygen has a tendency to attract electrons. Hydrogen atoms are the opposite; they have the property electro positivity, meaning they do the opposite of oxygen atoms. This means that they can form a perfect hydrogen bond. Boiling actually works by particles escaping the solution by escaping from the surface, which means that the particles at the bottom need more energy. When salt is added, the electronegative oxygen atoms go to the Na+ atoms and the oxygen atoms are attracted to them (intermolecular forces). This means that more heat is required to make them leave and get enough energy so the overall boiling point of the solution will increase.

There are some other factors that you have to consider but they require a really strong grasp of chemistry to understand.

Answer 2

the presence of impurities decrease the melting or freezing point of water but the nonvolatile impurities increase the boiling point and volatile impurities decrease the boiling point of water

Answer 3

impurities lower the magnitude of melting point of as substance.

And it increases the magnitude of boiling point.