Guide
1
With this in the problem and the amount of mass density is calculated as follows: m = V * p, where m - mass, V - volume, p - density.
2
In other cases, so expect a lot: m = n * M, where m - mass, n - quantity of substance, M - molar mass.The molar mass is not difficult to calculate, it needs to add up all the atomic weights of simple substances that make up the composite (atomic weights given in the table of Mendeleev on the designation of the element).
3
expresses the meaning of the mass from the formula of the mass fraction of substance: w = m (x) * 100% / m, where w - mass fraction of material, m (x) - weight substances, m - mass of the solution,wherein the substance is dissolved.To find the mass of the substance necessary: ​​m (x) = w * m / 100%.
4
The formula yield Compute your des
ired weight: yield = mp (x) * 100% / m (x), where mp (x) - weight of the product x, resulting in the actual process, m(x) - Calculate the weight of the substance x.Expose: mp (x) = yield * m (x) / 100% or m (x) = mp (x) * 100% / yield.With this in the problem of the product output, this formula will be required.If the yield is not given, then we must assume that it is equal to 100%.
5
If the present condition of the reaction equation, then solve the problem on it.To do this, first make a reaction equation, and then calculate the amount of a substance received or expended for the reaction and the amount of the substance is already in the desired formula substitute.For example, Na2SO4 + BaCl2 = BaSO4 + 2NaCl.It is known that the mass of BaCl2 is 10.4 g, you find a lot of NaCl.Calculate the amount of substance of barium chloride: n = m / M.M (BaCl2) = 208 g / mol.n (BaCl2) = 10,4 / 208 = 0,05 mole.From the reaction equation implies that 1 mole of BaCl2 formed 2 moles of NaCl.Calculate how much of the substance is formed from 0.05 mol BaCl2.n (NaCl) = 0.05 * 2/1 = 0.1 mol.The problem also needed to find a lot of sodium chloride, find pre-calculated molar mass of sodium chloride.M (NaCl) = 35.5 + 23 = 58.5 g / mol.m (NaCl) = 0,1 * 58,5 = 5,85, the problem is solved.