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How to calculate the mass fraction

how to calculate the mass fraction

Mass fraction shows a percentage or as a fractioncontent in substances which? a solution or composition of the substance in the element. The ability to calculate the mass fraction is useful not only to chemical classes, but when you want to prepare a solution or a mixture of, for example, for culinary purposes.

Or change the percentage, in your existing team.



Mass fraction is calculated as the ratio of the weight of this component to the total weight of the solution. To obtain the result as a percentage, it is necessary to multiply the resulting quotient by 100.
It looks formula is as follows:
? = M (solute) / m (solution)

?% =? * 100


Consider, for example, direct and inverse problems.
For example, you were dissolved in 100 grams of water, 5grams of salt. What percent solution you got? The solution is very simple. The mass of a substance (salt) you know the weight of the solution is equal to the sum of the masses of water and salt. Thus, it is divided into 5 g to 105 g, and the result of the division is multiplied by 100? it will answer: 4.7% solution you'll get.
Now the inverse problem. You want to cook 200 grams of a 10% aqueous solution of anything. How to take the matter to dissolve? In reverse order, the mass fraction, expressed divide by 100. We get 0.1 percent (10%). Now we compose a simple equation wherein the desired amount of the substance is denoted x, and hence a solution weight of 200 g + x. Our equation will look like this: 0,1 = x / 200g + x. When we decide that we get that x is equal to about 22.2, the decision to check the result of the direct problem.


It is more difficult to know what the number of solutionsknown interest must be taken to obtain a certain amount of solution given new qualities. It is required to compile and solve a system of equations already. In this system, the first equation - the expression of known weight of the resulting mixture in two unknown mass stock solutions. For example, if our goal is to obtain 150 g of the solution, the equation will have the form x + y = 150, the second equation? weight of the solute equated to the amount of the same substance, consisting of two mixed solutions. For example, if you want a 30% solution, and the solutions that you mix 100%, that is a pure substance, and 15%, then the second equation will be: x + 0,15y = '45 Case for small, to solve systems of equations and figure out how much to add substance to a 15% solution, to obtain a 30% solution. Try.

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