Mass fraction? And which one?

In the process of a chemical reaction , what is theoretically planned, at least quantitatively, is not always obtained. Usually this is due to the difficult reaction conditions - non-ideal temperature, insufficient contact with the catalyst and just chemical impurities of the reagents. In this case, chemists use the phrase "mass output share".

This concept includes a specific value - the percentage of practically obtained in relation to what would have been chemically produced. Denoted by the letter "omega". This value should be taken into account, often students forget to recalculate a small percentage. Particularly offensive is on all sorts of tests - the course of thought is correct, and a standard exam would allow most of the score for the task to be counted - and in testing it is on such little things that they "catch". Even give the answer options given this error. It's easy to get caught. So before you solve the problem, check whether there is a parameter "Mass fraction of output".

There are other, similar sounding concepts. The term "mass fraction" itself can be combined with other terms. And then, for example, the proportion of the substance in the ore is obtained. That is, you have a piece of material in which only some part can react. And this need to be taken into account in the calculations, otherwise you risk falling into the trap, as with the notion of "mass share exit." Also catch successfully and many. Caution!

Is there a mass fraction of the element in the compound? This means that its atoms make up a certain fraction of the mass in the substance. In principle, the chemists and lovers of complex solutions can use the mass fraction for calculations on the reaction equations. Another practical value this information can have, if you need to establish a formula for the substance. Just be careful - there are substance-isomers and substances with a similar proportional formula. You will need chemical reactions to establish the exact formula. But this level is not a school, but an olympiad in chemistry.

In reality, usually, all tasks are much simpler, students are checked for knowledge of the elementary formula and the ability to perform simple mathematical operations, not forgetting the number of atoms per molecule. How is the mass fraction of the element calculated? From the table, find the atomic weight of the desired element, multiply by the exact number of atoms in the molecule. This is the numerator. And in the denominator there should be a molecular weight of a unit of substance of the whole formula, that is, your element with the necessary factors and all other masses of elements multiplied by their number in the molecule. For example, the molecular weight of the water molecule is 16 (oxygen), add two hydrogen atoms (1 + 1). Total 18. The mass fraction of the hydrogen element is simple: divide 2 by 18. If necessary, multiply by one hundred percent, but in fractions of a unit, you can also. By analogy, do also in more complex formulas, when the elements are three or more.

The mass fraction as a concept is also used for solutions. The numerator is the mass of the dissolved, the denominator is the mass of the solvent plus the mass of the dissolved.

If you are attentive and understand each of the possible cases, you will not be slapped on the elementary one. And will not be offended because of a low score, when everything seems to be decided, but the result is not happy. Just do not miss these terms out of sight. Learn and practice on specific tasks. When you type your hand, all the difficulties will be in the past.