Today we continued to study chemical reactions – and looked at two classification schemes. The classification scheme used for Basic Chemistry sorts reactions into Synthesis, Decomposition, Single Replacement, Metathesis (Double Replacement) and Combustion. Our textbook takes a different approach and recognizes Acid-Base reactions, Precipitation reactions and Redox reactions. We will study redox reactions in more detail later in the course.
Helpful facts:
- Not all reactions are redox reactions – atoms (at least two) have to undergo changes in oxidation state for a reaction to be classified this way. Having said this – all single replacement reactions are redox reactions. Metals are oxidized to ions, and in the case of chlorine reacting with hydrogen bromide – the chlorine is reduced to chlorine ion (1-).
- Metathesis (Double displacement) reactions are NOT redox reactions. Sometimes they are precipitation reactions – if a precipitate is formed. Sometimes they are acid/base reactions and water if formed.
- Most decomposition reactions and synthesis reactions will be redox reactions.
We learned about total molecular reactions, total ionic reactions and net ionic reactions. These terms related to the analysis of a precipitation reaction. To correctly predict precipitates you must know the solubility rules (Table 4.1).
A variety of demonstration reactions were carried out today.
- 95% denatured ethyl alcohol is combusted in a Blaster Ball Canon
- 3M H2SO4 is added dropwise to pieces of mossy zinc
- Barium nitrate is combined with sulfuric acid to produce barium sulfate, an insoluble white precipitate used to coat tissues for diagnostic purposes.
- Milk of Magnesia is diluted with water, universal indicator is added to the mixture, 6M HCl is added in small portions and the solid is dissolved as it neutralizes the acid.
- Yellow chromate and orange dichromate can be interconverted by adjusting the pH using HCl and NaOH.
Reminder:Quiz tomorrow covers reactions and stoichiometry. There are practice quizzes posted.
>Reminder: Lab tomorrow – please don’t wear sandals. Come prepared.
Did I forget any?