COMMON MISCONCEPTIONS
Students may think that the substance that is oxidized is the oxidizing agent and similarly the substance reduced is the reducing agent.
- Students may follow along the logic that because reduction means to lose something, then intuitively it must mean that we lose electrons whereas reduction is actually gain of electrons. The best way to avoid this confusion is to provide students with the following acronyms: OIL RIG (oxidation is losing and reduction is gaining of electrons) or LEO GER (losing electrons is oxidation and gaining electrons is reducing)
A common misunderstanding for students is that the oxidation numbers represent an ionic charge in a polyatomic ion or a covalent molecule. This is not the case. Instead Oxidation numbers are imafinary numbers that were invented for purpose of keeping track of electrons. When chemist assign oxidation number they assume that electrons in a bond spend all their time around a more electronegative element. Additional confusion may arise from the notation that oxidation number is the same as the common charge for some elements (i.e. Cl‑) To help address this area of confusion the teacher should have strict rules which tell studnets wehre to place the charge.
Students may think that oxidizing agent or reducing agent are always just a single atom or ion.
- The ionic charge must always be written following the number (Ca2+)
- The oxidation numbers are always written with the charge in front of the number (Ca+2)
- Oxidation numbers do not always have to be whole number and this can be illustrated via the formation of magnetite (Fe3O4), which is combination of iron (II) and iron (III).
Students may think that oxidizing agent or reducing agent are always just a single atom or ion.
- This is not true. Let students know that if a molecule is oxidized (i.e. CH4), the reducing agent will be CH4.
Students may not be unclear about the difference between voltage and electric current.
- This is an excellent video:
Students may have misunderstanding that the anode is always shown left.
A major student misconception is that free electrons can travel through an electrolyte solution.
The energy comes from the fruits
- Please that this misconception of anode on the left only applies short hand notation when representing galvanic cells. Show students a diagram of a voltaic cell, the anode can appear on left or the right. Remind them that in a laboratory setting the anode can be on any side so do not assume that the left side is the anode.
A major student misconception is that free electrons can travel through an electrolyte solution.
- Free electrons do not flow through the electrolyte in a cell. The flow of electric current in a cell involves the flow of anions and cations and a redox reaction (reduction at the cathode and oxidation at the anode). Please tell students that the diagrams that they see are showing the flow of ions through the electrolyte not the electrons.
The energy comes from the fruits
- The energy comes from the chemical change in the zinc. The energy comes from the chemical change in the zinc when it dissolves into the acid. The zinc is oxidized inside the lemon, exchanging some of its electrons with the acid in order to reach a lower energy state, and the energy released provides the power
Students may think that half cells do not need to be electrically neutral, but that one half cell can be positive with cations and the other half cells can be negative with anions.
- Explain that ions migrate in the internal circuit whereas electrons flow in the external circuit which maintains electrically neutral half cell compartments.
Students may think cell potential can used to deduce the spontaneity of a reaction.
- Spontaneity reaction does not always have to take place because a high amount of activation energy may be required or a more favourable reaction may occur.
Reference Common Misconceptions
- Chemistry 12 Balushi et al. 2012. Omani twelfth grade students’ most common misconceptions in chemistry. Science and Education International. 23:3, 221-240
- http://sch3u-aq.wikispaces.com/Senior+Chemistry+ABQ
- Main header image
- http://upload.wikimedia.org/wikiversity/en/6/6f/Oil_rig.png