SAT Subject Test Chemistry
PART 2
REVIEW OF MAJOR TOPICS
CHAPTER 4
Chemical Formulas
WRITING IONIC EQUATIONS
At times, chemists choose to show only the substances that react in the chemical action. These equations are called ionic equations because they stress the reaction and production of ions. If we look at the preceding equation, we see the complete cast of “actors”:
Reactants
2HCl(aq) releases → 2H+ (aq) + 2Cl−(aq) in solution
Zn(s) stay as → Zn(s) particles
Products
ZnCl2(aq) releases → Zn2+(aq) + 2Cl−(aq) in solution
H2(g) stay as → H2(g) molecules
Writing the complete reaction using these results, we have:
2H+(aq) + 2Cl−(aq) + Zn(s) → Zn2+(aq) + 2Cl−(aq) + H2(g)
Notice that nothing happened to the chloride ion. It appears the same on both sides of the equation. It is referred to as a spectator ion. In writing the net ionic equation, spectator ions are omitted, so the net ionic equation is:
2H+(aq) + Zn(s) → Zn2−(aq) + H2(g)
TIP
In net ionic equations, do not show “spectator” ions that do not change.