September 19th - The Classification of Matter

We kicked off today’s class by reviewing chemical equations and balancing. During this time we encountered an interesting chemical reaction:

            MgSO₄^.6H₂O --> MgSO₄ + 6H₂O

This is called a hydrated compound or a hydrate. This is a compound that contains water molecules in their solid structure. The vertical ^. represents a weak bond between the water and the rest of the compound and is written in the vertical center of the line. The coefficient before water indicates the number of water molecules attached.

Shortly after, we moved on to the classification of matter. Nearly all matter can be classified as either a homogeneous substance or a heterogeneous substance. 

Homogeneous substances consist of only one visible component. Examples include:

• distilled water
• oxygen
• graphite
• air
• salt water

No matter how close we look at a homogeneous substance, there will be only one visible component.

On the other hand, heterogeneous substances contain more than one visible component. Examples include: 

• granite
• sand 
• cloudy water 
• blood

This flow chart can give you a better understanding of the classification of matter:

As shown in the diagram, there are two types of pure substances: elements and compounds. Elements are substances that cannot be broken down into simpler substances by chemical reactions. Examples include oxygen, iron, and magnesium. Compounds, on the other hand, are substances that are made up of two or more elements and can be changed into elements (or other compounds) by chemical reactions. This includes water and sucrose. In general, acids and bases are pure substances.

Determining whether something is an element or compound is not an easy task. The distinction is usually only visible at the atomic level. However, there are certain methods that we can use to find out the composition of a substance. 

In class, we witnessed an electric current pass through a bowl with a few pickles in it. When the electric current passed through the pickles, we saw sparks. When the current flowed through the water, electrolysis took place. Electrolysis split the compound, water, into its constituent elements.

Afterwards, we discussed what we knew about solutions. We learned that a solution is a homogeneous mixture of two or more substances. Solutions usually involve liquids, but don’t have to. We also learned about solvents and solutes. In a solution, the solvent is the component present in the great amount that does the dissolving. The solute is the component present in the smaller amount.

Our next topic was mixtures. Many mixtures are easy to identify, but some can be easily confused as pure substances. In heterogeneous mixtures, the different parts are clearly visible. In homogeneous mixtures, they are not (such as salt water, air, and brass).

There are many ways to separate mixtures, and they include:

• manually (by hand)
• filtration (heterogeneous mixture only)
• distillation
• crystallization
• chromatography 

All of the above methods are physical changes. 

Posted by Andrew.