This is the relationship between words like casa house and casita little house. Yet much of the time I was looking to put in roughly equal numbers of molecules. Solution— the mole! It was a snap to weigh each chemical I placed inside my reaction mixture. If you only remember one thing about the mole, let it be this: The mole is a bridge between the life-size stuff we experience every day and the universe of the very small.
This is a BETA experience. You may opt-out by clicking here. More From Forbes. Jul 23, , am EDT. Jul 15, , am EDT. Some current textbooks are examined for how they teach about the mole in order to compare the official definition to current educational practice. In order to put the likely effects of the proposed change into historical perspective, a comparison is made to effects from an earlier major change in SI for chemists, namely, the inclusion of the mole as an SI base unit in The Mole in Current Textbooks.
The mole is key content in every introductory chemistry textbook, and teaching the mole is a perennial subject in chemistry education. The current official definition of the mole reads 5 The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0. Here is the definition given in the draft of the new SI: 2 The mole, symbol mol, is the SI unit of amount of substance of a specified elementary entity, which may be an atom, molecule, ion, electron, any other particle or a specified group of such particles; its magnitude is set by fixing the numerical value of the Avogadro constant to be exactly 6.
The treatment within the body of a textbook includes examples, and relates the mole to mass as well as number of entities. The next paragraph says 8 The second, and more fundamental, thing to understand about the mole is how it gets its specific value.
Comparing the draft definition of the mole to current textbook treatments suggests two implications: 1.
The expectation that textbooks of the future will not change their definitions of the mole very much in response to the change in the SI definition is based partly on the fact that the draft SI is in some respects closer than the current definition to what many textbooks have already.
But it is also based on the fact that textbooks did not greatly change how they introduced the mole over the years. Consider textbook definitions from before the inclusion of the mole into the SI.
The term and unit mole had been in use in chemistry since roughly the start of the 20th century; 11 however, it was incorporated into the SI as a base unit, along with the base quantity amount of substance only in Mortimer happens to be the last example selected from this time period, but I do not want to imply that eventually textbook authors followed his example and adopted the official SI definition; examining recent textbooks as done above shows that this is not the case.
Indeed, this glimpse at how the mole has been described in textbooks over the past 50 years or so suggests that textbook authors have emphasized throughout that a mole contains a definite number of entities. Of Official Definitions and Textbooks. It may be that textbooks will not adapt to or reflect changes in official definitions of the SI. That would not necessarily be an unfortunate development. Let us look more closely at these assertions in the light of current practices and a few examples from the pedagogical literature.
Having concentrated above on the mole, what follows will focus on the quantity of which the mole is the unit, amount of substance. Let us begin our examination of official definitions with the SI Brochure. We have already seen the current and draft definitions of the mole.
Both the current and draft definitions say that the mole is an amount of substance. Thus, the current definition is implicitly an operational one: finding out the number of atoms of 12 C in 0. It does give the number of elementary entities in a mole, albeit in a way that no instructor of introductory chemistry would use that is, by giving the numerical value of the Avogadro constant. The definitions of units in the new SI are all explicit-constant formulations, which means that the units are defined indirectly by giving the value of a physical constant.
Thus, the draft SI Brochure does not say transparently that a mole contains exactly 6. The point to notice here is that these definitions are primarily concerned with formal relationships—of the mole to a standard mass of a standard material in the current SI , to a physical constant in the new SI , and to the physical quantity amount of substance in both.
The observation that educators tend to use other language, by the way, is not in itself a criticism either of the official definitions or of textbook formulations, but a reminder that using a text for one purpose when it was written for another may not produce optimal results. The SI Brochure is concerned with defining base units, and is less concerned about defining base quantities.
For example, it does not define either intuitive quantities such as length or more complex quantities such as thermodynamic temperature. Still, looking at a the entries for a few SI units and quantities shows that they are intended not primarily to teach concepts but to illustrate formal relationships. Here are the entries for mass and kilogram: mass , m : Base quantity in the system of quantities upon which SI is based.
Clearly, this is not the place to go to learn about the nature of mass. Let us examine the entry for amount of substance in some detail. The name of the quantity of which the mole is a unit serves as an example of the assertion that SI definitions do not necessarily represent the consensus of scientists.
It is clearly desirable to have a special term for the quantity of which the mole is a unit—a term that does not contain the word mole. At the same time, it is obvious that use of the official term for this quantity does not represent the consensus of practicing chemists. After all, the data set for this query was research papers published relatively recently—more than a generation after the introduction of amount of substance as an SI base unit—in peer-reviewed ACS journals.
How do you calculate the moles of a substance? How can I calculate the moles of a solute? What is an example a practice problem with moles? See all questions in The Mole. Impact of this question views around the world. My name is Avogadro, but all my friends call me Avi. You may have seen my adventures with my friends in Celebrating Chemistry. When we are not exploring, we go to Mole Hill Elementary School. He recently taught us what a mole is. A mole of something means you have ,,,,,,, of that thing!
Because this is a very big number, scientists shorten it to 6. How cool is that?! You may be wondering how chemists came up with a number like 6. Think of all the omelets you could make! They measure things that are really, really small like atoms, molecules, and other particles. Atoms are the building blocks of matter, and atoms can be connected to make molecules. Keep in mind that not everything weighs the same if you have a mole of it.
A mole refers to the number of particles you have, not the mass.
0コメント