In the process of a chemical reaction, what is theoretically planned is not always obtained, at least quantitatively. This is usually due to difficult reaction conditions - non-ideal temperature, insufficient contact with the catalyst, and simply chemical impurity of the reagents. In this case, chemists use the phrase "mass fraction of the yield."
This concept includes a specific value - the percentage of practically obtained in relation to what should have been chemically obtained. Denoted by the letter "omega". This value must be taken into account, often students forget to recalculate a small percentage. It is especially disappointing in various kinds of testing - the train 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 trifles that they “catch”. They even give options for the answer, taking into account such an error. It's easy to get caught. So before solving the problem, check if there is a “mass fraction of the output” parameter.
There are others, it seemssound concepts. The term "mass fraction" itself can be combined with other terms. And then it turns out, for example, the proportion of the substance in the ore. That is, you have a piece of material in which only a certain part can react. And this must be taken into account in the calculations, otherwise you risk falling into a trap, as with the concept of "mass fraction of the output." Also catch successfully and many. Watch out!
Is there a mass fraction of the element in the compound in the condition? This means that its atoms make up a certain percentage by mass in matter. In principle, for chemists and lovers of complex solutions, the mass fraction can be useful for calculations using reaction equations. This information can also be of practical value if you need to establish the formula of a substance. Just be careful - there are isomer substances and substances with a similar proportional formula. You will need chemical reactions to establish the exact formula. But this is not a school level, but a Chemistry Olympiad.
In reality, usually all tasks are much simpler, schoolchildren are tested on the knowledge of an elementary formula and on the ability to perform simple mathematical operations, not forgetting the number of atoms per molecule. How is the mass fraction of an element calculated? Using the table, find the atomic weight of the element you are looking for, multiply by the exact number of atoms in the molecule. This is the numerator. And the denominator should contain the molecular weight of a unit of the substance of the entire formula, that is, your element with the necessary factors and all other masses of the elements multiplied by their number in the molecule. For example, the molecular weight of a water molecule is 16(oxygen), add two hydrogen atoms (1+1). Total 18. The mass fraction of the hydrogen element is simply: divide 2 by 18. If necessary, multiply by one hundred percent, but in fractions of a unit it is also possible. By analogy, do it in more complex formulas when there are three or more elements.
Mass fraction as a concept is also used for solutions. The numerator is the mass of the solution, the denominator is the mass of the solvent plus the mass of the solution.
If you are careful and understand each of the possible cases, you will not be caught in elementary. And it will not be a shame because of a low score, when everything seems to be decided, but the result is not encouraging. Just keep these terms in mind. Learn and practice on specific tasks. Once you get your hands on it, all the troubles will be in the past.
