Sunday, 11 September 2011

Misconceptions about the Mole

  • Students confused about whether to treat a mole as a number or a quantity of matter
  • Students unable to visualize, work with such large numbers
  • A 2-mm-long line of atoms contains 6x10^23 atoms
(Horton, C. (2004). Student alternative conceptions in Chemistry. Arizona State University. Retrieved from

To promote conceptual change in learning the mole concept, conceptual change texts were prepared by the instructor and used with the experimental group in five steps. Some exemplary parts of the conceptual change texts are as follows:\

Step 1: Students were asked to define the term mole. Some of the student answers are given below:
--The atomic or molecular mass of a substance expressed in grams is 1 mole.
--Mass/molar mass or n = m/M (the ratio of mass to molar mass) is 1 mole.
--As many pencils as Avogadro's number (NA) is 1 mole.
--16 gram of oxygen atoms are 1 mole.

All of the statements above are correct, but none of them is the correct definition of the mole. The instructor made the correct definition of mole after receiving these answers from students. "A mole is an amount of substance that contains the same number of elementary units as there are [sup.12]C atoms in 12.00000 g [sup.12]C."

Step 2: In this step, the students were asked to define the atomic mass unit (amu). The following are some of the answers received from the students.
--The mass of any single atom is 1 amu or 1 amu = m/M.
--1 amu=1/NA (correct but not the definition of amu).
--1 amu=NA.

All of the statements above are correct, but none of them is the correct definition. The instructor gave the correct definition after receiving these answers from students. "1 amu is 1/12th of the mass of one [sup.12]C atom. According to this definition, the mass of one [sup.12]C atom is 12.00000 amu".

Step 3: The relationship between Avogadro's number, atomic mass unit and mass was explained in the following way: It was determined experimentally that there are as many [sup.12]C atoms as Avogadro's number in 12.00000 gram [sup.12]C, and the mass of one [sup.12]C atom was accepted as 12 amu according to the definition of amu. Given that 12 gram [sup.12]C is 1 mole (according to the definition of mole), the number of [sup.12]C atoms in 12 gram [sup.12]C is 6.02x[10.sup.23] (experimentally calculated). Then,

How many gram is 1 amu? (1 amu = ? gram)

12(gram)=(12x6.02x[10.sup.23]) amu (when both sides are divided by 12), l(gram)=6.02x[10.sup.23] amu, and hence, 1 amu=(1/6.02x[10.sup.23]) gram = 1.66x[10.sup.-24] gram.

Step 4: Relationship between molar mass and relative atomic mass was [sup.12]C Why is the number standing for molar mass in grams for any atom the same with the number standing for the relative mass in atomic mass units for a single atom?

Let us consider an argon atom. The true mass of an argon atom is 10/3 times the true mass of [sup.12]C atom. Namely, the relative mass of an argon atom is 40 amu (12 amu x 10/3=40 amu). According to the definition of mole, 6.02x[10.sup.23] Ar atoms is 1 mol. Hence, the mass of 1 tool Ar atom is equal to 40 x NA amu. Because 1 gram=NA amu, 1 mol of Ar atom is 40 gram. As a result, relative mass of 1 Ar atom is 40 amu and mass of 1 mol Ar atom is 40 gram.

(Uce, M. (2009). Teaching the mole concept using a conceptual change method at college level. BNET Australian edition. Retrieved from;col1)


  1. Hi girls,
    I taught this at my first prac. I found that using analogies was good eg, that one mole of feathers eg would weigh much less than a mole of bricks- yet both have the same number of 'particles'. It took some questions, lots of examples, and discussions , but by the end , most of the class 'got it'

  2. Leigh, that is exactly how I recall being taught the concept when I was in high school - an analogy such as that one makes it much easier for students to visualize and comprehend. I was lucky and was able to grasp the mole concept easily at the time, but I think that was because I am quite mathematical minded. From what I recall, the majority of my peers struggled with the concept in Chemistry, and the same students who struggled also did not study mathematics. I think this is something that you have to consider when teaching this concept. The approach to teaching this will change from class to class, depending on the backgrounds of the students. For those classes that might not be too fond of mathematics, an analaogy such as that one may be the best way to go about it.
    Did you start with the fun question of “What is heavier… a kilogram of feathers, or a kilogram of bricks?” Because some of the answers and explanations that people give for that question can be quite entertaining!
    - Scott Swindle

  3. I never learned the mole concept with the use of analogies and I think it would have been good if the teacher did use some because then I wouldn't have had so much difficulties in understanding. It wasn't until I did my first prac and had to teach the mole concept, that I used alot of analogies and it worked well. So I completely agree with the use if analogies. Thanks Neelam

  4. Thank you, thank you! I am not chemistry minded in the slighest,thus, I have struggled immensely with the concept of moles & molarity . I too was taught this concept in the traditional, purely logical/mathematical way(formulas & symbols only) and would have significantly benefited from the use of analogies, or anything that could make such an abstract concept more relevant to me! From my readings, I can associate my own/other students' inability to comprehend key chemistry concepts i.e molarity, bonding, structure of molecules etc to the inability to visualise or 'make sense' of what is occuring.

    When it comes time for me to teach these concepts, I will endeavour to make the tasks as relevant, visual and accessible to all students (as I possibly can). Hopefully I can make learning these concepts that little bit easier. Here's hoping anyway!

  5. It was quite fun and exiting way to teach the concept of moles. I was wondering as to how important it is to know the molecular weight of the chemicals taking part in the reaction?


  6. When I did my prac last semester, the teacher had just taught moles to her year 11 students, and the students were having great difficulties with the calculations. The teacher also used analogies to explain the concept, but the problem was that most of the students were doing general math, or no math at all. I think she spent a good 6 lessons and the students (approx 20) and they still didnt do that well in the class test. I think it is important that students understand that maths plays an important part in chemistry, and that it is hard work and very abstract, because the teacher tried everything including lunch tutorials, extra work for students who wanted it etc.

    I guess you'd have to inform the year 10's when they're choosing their subjects as well as the parents, because some students get forced to do subjects they are not able to comprehend.

    Madena Siddiqi

  7. You brought up a very good point Madena.
    In the previous school that i went to, the teacher had lots of difficulty teaching the mole concept, basically because the students did not have basic mathematical understanding or chemistry for that matter. It's very hard when they don't grasp simple concepts form year 7-10 and then do Chemistry in 11 and 12 just beacuse they don't have a choice or don't know what subjects to take.

    The teacher took many lessons to teach the class the concept and yet the students were not able to understand the concept, even though it was put very simply.
    -Neelam and Ponni

  8. Hi Sunny,
    molecular weight is very important because without it you would not be able to calculate the number of moles. and without the number of moles, you will not be able to calculate the mass.
    Therefore, it is also important to tecah students how to calculate molecular weight of compounds or molecules.
    -Neelam and Ponni

  9. Alana,chemistry can be difficult, especially with concepts like moles and molarity, like you mentioned so I think using different type of learning aids such as internet, visuals, models will be helpful. Also because as Madena mentioned, maths is involved and many students don't realise the importance of it when balancing equations and calculations, etc. We need to make sure students realise that chemistry isn't just mixing chemicals but much more. Neelam and Ponni

  10. I have a mathematical mind, and so I found formulae to be quite easy to understand. I did like how you elaborated that a mole is a way of describing a quantity.
    Some of the students I have taught (and assist in classrooms now) have difficulty explaining how 1 moles of two different substances (so 2 moles) could form 1 mole of something else.
    Alot of the students I have talked to, don't understand how 1 mole of oxygen atoms doesn't represent one mole of water molecules.
    What strategies would you use visually to address this misconception?

  11. I don't recall being taught the mole concept using anlaogies either, however, I do remember it being made very clear that 1 mole of a substance is not the same as 1 mole of another substance. I think this definitely the basis of some misconceptions. I believe that my teacher helped dispel this misconception by getting us to refer to the Periodic table when making calculations.

    Understanding what the components in the formaula n = m/M is crucial as is an appreciation of their relationship.

    I also think that further misconceptions creep in when c = n/v and/or c1v1 = c2v2 are introduced.