Common Misconceptions
There are a number of misconceptions that arise when teaching systems in equilibrium. Listed below are common misconceptions that may be encountered along with suggested activities-and where they are located in the lesson sequence provided if applicable-that may help address these misunderstandings.
1. Students commonly believe nothing is happening at equilibrium.Students learn in previous chemistry classes that reactions go until completion and have difficulty understanding that at equilibrium, forward and reverse reactions are still occurring but at the same rate such that the overall concentration of reactants and products remain constant. In the lesson listed below, students preform an activity using wads of paper to illustrate the movement of products and reactants at equilibrium This activity, when used in conjunction with plots of concentration, helps negate this misconception. Please click below to be redirected to this activity.
2. Students have difficulty understanding Le Chatelier's Principle as a reaction to a disturbance.
Students commonly confuse the disturbance of an outside force on a system as the new reaction conditions and will indicate a shift in equilibrium to accommodate this disturbance instead of a shift to counteract it. In the lesson listed below, students preform a "thought experiment" to have them think in terms of counteracting a disturbance, followed by a simulation to illustrate this concept. These two teaching strategies, when used in conjunction with each other, help to negate this misconception. Please click below to be redirected to this activity.
3. Students commonly believe equilibrium constants are constant under all conditions.
|
Students commonly take the word constant as golden, in the sense that they believe constant means constant, regardless of conditions. In the lesson listed below, students are given the chance to explore changing equilibrium constants with changing reaction conditions through an activity involving computer simulations in order to help negate this misconception. Please click below to be redirected to this activity.
4. Students commonly believe the addition of more solid will increase the concentration of aqueous species.
Students commonly believe that when examining solubility, the addition of more solid will result in more ions in solution. This is due to a misunderstanding of the concept of saturation. In the lesson listed below, students are given an opportunity to examine the effect of the addition of more solid to aqueous solutions through an activity involving computer simulations in order to help negate this misconception. Please click on the link below to be redirected to this activity.
|
5. Students commonly believe substances containing H+ are acidic and substances containing OH- are basic.
Students commonly believe that all solutions containing H+ are acidic and that only substances containing OH- are basic. They often think in terms of the substance rather than its affect on the system solution. This typically occurs due to the fact that they can understand (or validate their understanding) of acids and bases with the Arrhenius theory of acids and bases-commonly introduced first-and cannot integrate the Bronsted-Lowry theory that follows. This misconception can be cleared up relatively easily if addressed during a lesson on salt solutions. In the lesson listed below, students investigate the properties-including the pH-of soluble salts. It can be noted in the lab explanation that not all of these salts contain H+ or OH- ions and then reinforced by noting that it is the resulting effects on the water component of the solution that governs the pH not the components of the salts themselves. Please click below to be redirected to this activity.
6. Students commonly believe that when a `proton donor' acid reacts, the nucleus of an atom loses a proton.
Students have inherent difficulty with the term "proton donor" as it does lend itself to a visual image of a proton being donated. This difficulty is due to the misunderstanding of Bronsted-Lowry definition of acids and bases. Students often have trouble understanding this definition in terms of proton exchange reactions instead of proton "donations". They also commonly have difficulty recognizing the important consequences of this definition-specifically that a substance cannot act as a "donor" without the presence of an "acceptor" and vice versa. It is advised to address this misconception as an integral part of a lesson and highlight that it is an H+ ion being donated from one species to another, not a proton from one nucleus to another. In the lesson given below, students can observe this transfer using through the use of a computer simulation that shows the exchange of H+ ions in solution from one species to another. This can help negate this misconception if highlighted appropriately. Please click below to be redirected to this activity.
|
7. Students commonly believe that a weak acid is a diluted acid or that strength and concentration mean the same thing.
Students commonly assume, based off of previous knowledge of molar concentration and dilution of strong acids in laboratory settings, that a weak acid is nothing more than a strong acid diluted. This is due to a fundamental misunderstanding of the nature of acids and bases and the definition of strong and weak acids. Students are used to thinking of the terms strong and weak in relation to concentration rather than related to dissociation in solution. In the lesson listed below, students are given the opportunity to "view" the difference between strong and weak acid/bases in terms of concentrations of dissociated ions and non-dissociated molecules in solution, which can aid in negating this misconception if highlighted appropriately. Please click below to be redirected to this activity.
8. Students commonly believe that pH is a measurement of the degree of acidity of a solution.
Students commonly have difficulty understanding the relationship between the mathematical measurement of pH and the concentration of H+ or OH- ions in solution. They often assume that because the calculation of pH involves H+ ions that it must only be for acidic solutions. In the lesson listed below, students are given the opportunity to explore the nature of pH using a computer simulation. As they play with the pH of a variety of solutions they are able to see both the resulting H+ concentration but also the OH- concentration, for both "acidic" and "basic" solutions-which can help negate this misconception if highlighted appropriately. Please click on the link below to be redirected to this activity.
|
9. Students commonly believe that an acid eats material away and only an acid can burn you.
Given the portrayal of acids in movie and media, students assume that all acids can burn your face off and only acids are dangerous. Students have very little exposure to the properties of bases and as such, commonly assume that bases are "safe". The easiest way to negate this misconception and initiate a discussion as to the properties of acids and bases-ideally as part of the introduction to acids and bases and their properties-would be to show a movie or demonstration of the power of bases. Click below to be redirected to a movie that uses caustic soda (NaOH) to illustrate this concept and can be used to negate this misconception. This could also be done very easily as a demonstration if classroom conditions can warrant it.