Greenenvironmental's Blog

Chemical Properties
All chemicals have unique properties that allow us to tell them apart.  These properties include color, density, solubility (oil and water don’t mix), boiling point, melting point, conductivity, and many others.

Some properties are unique, and make it easy to identify that particular chemical, like the density of gold.  Other chemicals are so similar that only very sophisticated means can be used tell them apart.  It is similar to telling different people apart: black and white people are easy tell apart, but identical twins take more effort.  Many similar chemicals are grouped together, like PCBs and dioxins, which are names given to similar groups of chemicals, not individual chemicals.  Gasoline, for example, is a mixture of thousands of different individual chemicals, ranging from alkanes (like octane) to polycyclic aromatic hydrocarbons (PAHs), but we tend to think of gasoline as one chemical.

Properties can be measured, or ‘quantified’ (given a quantity).  This gives us more specific information than ‘qualities’ like heavy, or dark.  For example, gold has a quantified density; so that while lead is ‘heavy’, it is not as heavy as gold, and we can measure the difference.  This originated with the need to distinguish counterfeit coins from real ones, someone came up with the concept of density.

In the end, there are only seven different ways we can measure something:

Length(m)
Mass(kg)
Time(s)
Temperature(K)
Amount of substance (mole)
Luminous intensity (candela)
Electric current(ampere).

We can then put these seven basic measurements together in an almost infinite variety of ways, and these are called derived units:  Speed is length per time, acceleration is length per time squared, Concentration is moles per volume (length cubed), Density is mass per volume, and Force is mass times acceleration.

States of matter
All chemicals come in a certain ‘state’ under normal conditions; it is one of their identifying properties.  Matter can be liquid, solid, gas, or plasma.  For example, mercury is in a liquid state under normal conditions, while almost all the other metals are in a solid state.  Pure ‘oxygen’ and ‘nitrogen’ are in a gas state, while water is in an in-between state; sometimes in all three states at once.  Snow, for instance, is the solid form of water, while ‘wet snow’, or slush, is part liquid.  Additionally, snow can ‘sublimate’, (solid evaporates right into a gas without becoming a liquid first), so, all three states can be present in a patch of snow at the same time.

Chemists often use ‘phase diagrams’ to determine what state a chemical will be in under certain temperatures and pressures.  For example, water will boil at very low temperatures if the pressure is low enough, or, it will boil at higher temperatures if the pressure is higher; Pressure Cookers utilize this property.  Phase diagrams also help engineers design materials for various applications, like which materials will make the best ‘heat shields’ for space craft.

Solutions
Most of the chemicals we use are in the form of a solution.  Orange juice is a good example of a solution, it consists of water, plus a whole lot of other stuff like pulp, vitamins, and minerals.  Our bodies are big bags of solution, and according to aliens on Star Trek, we are ‘ugly bags of mostly water’.

The stuff mixed in water is said to be dissolved in the water, like dissolving sugar into coffee.  Water is called the universal solvent because it will dissolve anything.  Further, water dissolves different amounts of different substances, and how much it dissolves often depends on what the temperature is.  For example, Rock candy is made by pouring sugar into boiling water, and then letting the water cool.  As the water cools, it cannot hold as much of the sugar any longer, so the sugar must come out of the solution.  It does this by forming crystals, and we can evaporate off the water to leave the crystals.  On the other hand, oxygen dissolves to the maximum amount when water is near freezing,  less can be dissolved as the temperature is raised.

This is how stalagtites and stalagmites are formed in caves. The water seeping through the earth dissolves the most ‘soluble’ mineral parts of the bedrock, and leaves the rest. This solution can  enter a cave where the minerals crystalize out of solution as the water evaporates away inside the cave.

Solubility: Oil and water don’t mix

The use of this property is a good way to identify compounds like gasoline: if we put some gasoline in a glass of water it will float on top of the water.  It does not appear that the ‘oil-like’ gasoline and the water mix, they ‘separate’.  Technically, water will dissolve even oil, but it does not dissolve enough to matter for Identification; a tiny amount of gasoline will dissolve into water,  not enough to fuel a fire, but it will make the water taste like crap (our senses are very sensitive to compounds like gasoline), and kill fish.  Similarly, compounds like ‘dry-cleaning’ solvents don’t mix with water either, however, they sink to the bottom of a glass of water instead of floating on top.   Another ‘sinker’, is the heavy part of petroleum, called DNAPL, or Dense Non-Aqueous Phase Liquid.

This is why if you step in tar at the beach, washing it off with water will not help.  What is needed is a substance that allows oil and water to mix, like soap or alcohol.  ‘Like dissolves Like’ is a concept chemists use, and is similar to saying oil and water don’t mix.   Soap, and alcohol, are chemicals that act like a bridge; they have a water like end(hydrophilic), and an oil like end(lipophilic).  The oil like end dissolves oil-like compounds(like dirt and tar), while the other end dissolves in water allowing the substance to be ‘washed out’.  This is the principal behind washing clothes, with no soap you only get the clothes wet.

Reactions
There are two  types of reactions chemicals can undergo.  A physical reaction leaves the chemical unchanged, like evaporation.  A chemical reaction leads to new chemicals, like burning meat versus cooking it.

Another way we can tell chemicals apart is by how they react with (or interact with) other chemicals: Gasoline will react with air and a spark to create fire; Acids will react with bases (but not usually other acids) releasing heat and sometimes hazardous gases;  Sodium metal will react violently with water, and crystals like picric acid can explode with friction (like unscrewing a cap with some crystals in the threads (a major hazard when dealing with old bottles in a chemistry lab).  The DOT ‘hazard classes’ are based on the types of reactions certain chemicals will undergo so that they may be handled more safely.