# Advice 1: How to find the mass of the substance

The mass of the substance is required in many tasks. This can be done by using special formulas. Usually the problem is present in the reaction, which are some of the values. Instruction
1
If this the problem the volume and density calculate the mass as follows: m = V*p, where m – mass, V – volume, p – density.
2
In other cases calculate the mass: m = n*M, where m is the mass, n is amount of substance, M is the molar mass. The molar mass is not difficult to calculate for this you need to add up all the atomic masses of simple substances into the complex (atomic mass listed in the table of D. I. Mendeleev on the designation of the element).
3
Express the mass value from the formula the mass fraction of the substance: w = m(x)*100%/m, where w is the mass fraction of the substance, m(x) is the mass of the substance, m is the mass of the solution, in which dissolved the substance. To find the mass of the substance is required: m(x) = w*m/100%.
4
From the formula of the product yield calculates the desired weight yield of product = mp(x)*100%/m(x), where mp(x) is the mass of the product x, obtained in the process, m(x) is the calculated mass of the substance x. Output: mp(x ) = product yield* m(x)/100% or m(x) = mp(x)*100%/ the output of the product. When given in the problem statement yield this formula will be needed. If the output of the product is not given, assume that it is equal to 100%.
5
If the condition is present in the reaction equation, then solve the problem on it. To do this, first make the reaction equation, then calculate from it the amount of substance received or expended for this reaction and already is the amount of substance put in the right formula. For example, Na2SO4 + BaCl2 = BaSO4 + 2NaCl. It is known that the mass of BaCl2 is equal to 10.4 g, you need to find the mass of NaCl. Calculate the amount of substance of chloride of barium, n = m/M. M (BaCl2) = 208 g/mol. n(BaCl2) = 10,4/208 = 0.05 mol. From the reaction equations, it follows that 1 mole of BaCl2 was formed 2 mol NaCl. Calculate what quantity of matter is formed from 0.05 mol BaCl2. n(NaCl) = 0,05*2/1 = 0.1 mol. In the task they needed to find the mass of sodium chloride, find pre-calculating the molar mass of sodium chloride. M(NaCl) = 23+35,5 = 58,5 g/mol. m(NaCl) = 0,1*58,5 = 5,85 g. the Problem is solved.
Note
Units of mass can be milligrams, grams, kilograms.

# Advice 2 : How to find mass if the volume and density

The mass of a body is its most important physical characteristic. In modern physical science, there is a distinction between the concepts of "mass" gravitational mass (as the degree of impact of a body on the earth's gravity) and inertial mass (how much effort will be required in order to bring the body from a state of inertia). In any case, to find the mass very easily, if you know the density and volume of the body. Instruction
1
In that case, if the body is known to such indicators as the volume (V) and density (p) for calculating the body mass will need to use the formula: m = p*V.
2
For clarity, you can give an example. You want to find the mass of a concrete slab whose volume is 15 m3.
Solution: for finding the mass of the concrete slab is required to know only its density. In order to learn this information, you need to use a table of densities of various substances.
3
According to this table the density of concrete is 2300 kg/m3. Then to find the mass of the concrete slab, you will need to perform simple algebraic action: m = 15*2300 = 34500 kg, or 34.5 tons. Answer: the mass of the concrete slab is 34.5 tons
4
Mass measurement in the traditional way using one of the oldest instruments of mankind - with the help of weights. This is due to the comparison of body weight with the reference weight of cargo weights.
Note
Compute by the above formula, you must realize that in this way is known the rest mass of the body. An interesting fact that many elementary particles have an oscillating mass, which depends on the speed of their movement. If an elementary particle moving with the speed of the body, this particle is massless (e.g. photon). If the speed of motion of the particle below the speed of light, such a particle is called massive.