General Chemistry 1 Section 1.3: Properties of Matter
Hello internet, and welcome to the Science of Life General Chemistry lecture series. In this session, I'll cover some of the properties of the materials in which chemists are interested.
Properties
There are two types of properties which we deal with in General Chemistry. There are more types, but there are specifically two that are important for this course. There are physical properties (properties which do not describe the chemistry of the substance, such as the phase) and chemical properties (which do describe the chemistry of the substance, such as whether or not it's an acid). Properties can also be classed as either extrinsic (depends on the quantity of the substance, such as the mass) or intrinsic (does not depend on the quantity, such as melting point). Boiling point is an intrinsic physical property; it doesn't describe the chemistry of the substance (alas the physical part) and the boiling point at that pressure doesn't change with quantity of substance (alas the intrinsic part). Being an acid is an intrinsic chemical property since it does describe the chemistry and it doesn't depend on the amount of the substance. Volume is an extrinsic physical property since it doesn't describe the chemistry and it does depend on the quantity.
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| Flow Chart of Properties and Changes. |
Changes
A physical change is a change of only the physical properties of a substance, but not its composition. A good example of this is the boiling of water. The water is changing from liquid to a gas (changing it's state, a change in its physical properties). A chemical change (also called a chemical reaction) is one where the composition of a substance is changed, regardless of how that change occurs and regardless of whether or not a physical change occurs.
A great example is the electrolysis of water converting H2 to H2 and O2 making two molecules of H2 and one molecule of O2 for every two molecules of H2O, which also happens to change the physical properties as well. In this case, the physical changes are caused by the presence of compounds which are now different than all compounds which were there before. The reaction itself did not cause the physical properties to change, but the difference in chemical properties does cause the differences in physical changes.
Another example is the reaction of NaOH with HCl to produce H2O and NaCl, where there is no apparent change of physical properties (except possibly density). There may not be any apparent changes in physical properties, but any which may be apparent would be caused by the differences in chemical properties.
Since each component of a mixture retains its own physical properties (as mentioned last time), we can separate the components of a mixture using these physical differences. This could mean a difference in solubility. After all, sand is insoluble in water, but salt is not. what we could do if sand and sugar were mixed together is to pour in some water, stir it about, and filter it. We could use differences in magneticism to use a magnet to lift iron filling from gold fillings. Another good separation technique is taking advantage of the differences in boiling point, which is the process of distillation.
A great example is the electrolysis of water converting H2 to H2 and O2 making two molecules of H2 and one molecule of O2 for every two molecules of H2O, which also happens to change the physical properties as well. In this case, the physical changes are caused by the presence of compounds which are now different than all compounds which were there before. The reaction itself did not cause the physical properties to change, but the difference in chemical properties does cause the differences in physical changes.
Another example is the reaction of NaOH with HCl to produce H2O and NaCl, where there is no apparent change of physical properties (except possibly density). There may not be any apparent changes in physical properties, but any which may be apparent would be caused by the differences in chemical properties.
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| They may be different concepts, but they're still equally skillful at messing up your life. |
Separation
One vital aspect of chemistry is the concept of separation. After all, in the practical application of chemistry, we would like absolute control of the atoms and molecules we are using. We want to make sure that when we are putting an ounce of salt into water in order to make a mouth rinse, the ounce of white stuff is pure salt as opposed to sugar or a mixture of sugar and salt.Since each component of a mixture retains its own physical properties (as mentioned last time), we can separate the components of a mixture using these physical differences. This could mean a difference in solubility. After all, sand is insoluble in water, but salt is not. what we could do if sand and sugar were mixed together is to pour in some water, stir it about, and filter it. We could use differences in magneticism to use a magnet to lift iron filling from gold fillings. Another good separation technique is taking advantage of the differences in boiling point, which is the process of distillation.
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