Phase Notation
Dr. MJ Patterson
The phase (solid, liquid, gas, aqueous solution) of a chemical plays a
significant role in its reactivity. Chemists have developed a shorthand to indicate phases by placing an abbreviation in
parentheses as a subscript following the formula for the chemical.
|
Phase |
Symbol |
|
solid |
s |
|
liquid |
l |
|
gas |
g |
|
aqueous solution |
aq |
(An aqueous solution is one in which the solvent is water.)
Example 1:
How would you indicate ethyl alcohol C2H6O as a solid,
liquid, gas and aqueous solution?
Solution 1:
Use the phase symbol in parentheses and as a subscript following the compound's
formula:
solid = C2H6O(s)
liquid = C2H6O(l)
gas = C2H6O(g)
aqueous solution = C2H6O(aq)
Example 2:
Write and balance the equation to show pure ethyl alcohol (normally a liquid)
dissolving in water to make an aqueous solution.
Solution 2:
Since ethyl alcohol is a molecular compound (all nonmetals), when it dissolves
in water, it stays intact as molecules.
C2H6O(l)
=>(H2O) C2H6O(aq)
(Chemists frequently write reaction conditions, solvents, catalysts or other important information above the arrow in a reaction. Since it is difficult to do that over the web, I will write any information like this in parentheses immediately after the arrow, such as the water in this example.)
Example 3:
Write and balance the equation to show Epsom''s salt
MgSO4 (normally a solid) dissolving
in water to make an aqueous solution.
Solution 3:
Since magnesium sulfate is an ionic compound (metal + polyatomic ion), when it
dissolves in water, it dissolves as separate ions.
MgSO4(s) =>(H2O) Mg2+(aq) + SO42-(aq)
Review Question:
In the previous two examples, we encountered a difference in the way that
molecular compounds and ionic compounds behave when dissolved in water.
What are the criteria for recognizing an ionic compound versus a molecular
compound?
Review Solution:
An ionic compound is a metal + a nonmetal, or it contains one or more
polyatomic ions. A molecular compound consists of only nonmetals.