Chemistry — the exact science therefore when mixing various substances it is just necessary to know their accurate proportions. For this purpose it is necessary to be able to find the mass of substance. It is possible to make it in various ways, depending on what sizes are known to you.
Instruction
1. With the known values of volume and density of the available substance use the simplest way for finding of weight — increase substance volume by its density (m(x) = V*p).
2. If values of molar mass of substance and its quantity are known to you, apply other formula to determination of mass of substance, having increased value of amount of substance by its molar weight (m(x) = n*M). If the amount of substance is unknown, but the number of molecules in it is given, then use Avogadro's number. Find amount of substance, having divided number of molecules of substance (N) into Avogadro's (NA=6.022x1023) number: n=N/NA, also substitute in a formula above.
3. To find the molar mass of complex substance, put atomic masses of all simple substances which are its part. Take atomic masses from D.I. Mendeleyev's table in designations of the corresponding elements (for convenience round atomic masses to the first figure after a comma). Then act in a formula, having substituted value of molar weight there. Do not forget about indexes: what index of an element in a chemical formula (i.e. how many atoms in substance), on it is necessary to increase atomic mass so many.
4. If it is necessary to deal with solution, and the mass fraction of the necessary substance is known to you, for determination of mass of this substance increase a mass fraction of substance by the mass of all solution and divide result into 100% (m(x) = % w*m/100).
5. Work out the substance reaction equation, from it calculate amount of the received or spent substance, and substitute the amount of substance then received in the formula given you.
6. Apply a product yield formula: exit of =mp*100%/m (x). Then, depending on the weight which is required to be calculated you find mp or m. If the product yield is not given, then it is possible to accept it equal 100% (in real processes meets extremely seldom).
7. Calculate weight on Mendeleyev-Clapeyron's equation for gases: PV=m(x)RT/M if in a statement of the problem the volume and pressure are specified.