In chemical reactions the smallest particles (atoms, molecules), and their number even take part in a small portion of substance it is very big. Therefore for simplification of calculations the special unit of measure of ""amount of substance"" - mol was entered. 1 Mol contains 6.02*1023 atoms or molecules. How to calculate the mass of substance?
It is required to you
- - substance;
- - Internet;
- - Mendeleyev's table.
Instruction
1. Define what type of weight to you it is necessary to calculate: usual, molecular or molar. Find a formula of chemical compound which lot you need to calculate. If it is not in a task, start search in the name on the Internet.
2. Count amount of the chemical elements entering a molecule of the substance interesting you. For example, sulfate aluminum Al2(SO4)3 consists of two atoms of aluminum, three atoms of sulfur and twelve atoms of oxygen.
3. Open Mendeleyev's table. Atomic mass is specified for each element under its alphabetic reference, round exact numbers from the table when calculating to the next whole. So, the atomic mass of aluminum = 27 (26.98154 according to the table), are gray = 32 (32.06 in the table), oxygen = 16 (15.9994). Write down the atomic mass of each of elements. Molecular weight is equal to the sum of atomic masses of all elements of substance, taking into account their quantity in connection.
4. Put atomic masses, multiplying each of them by amount of this chemical element in a formula, you receive the molecular mass of substance: 2Al + 3S+12O = 2*27+3*32+12*16 = 342 Molecular weight have no unit of measure.
5. For determination of usual mass of a number of substance it is necessary to know molar weight (the mass of one of this connection, it is expressed in grams on mol, g/mol, and it is directly connected with molecular weight). For this purpose to the received value of molecular weight just add ""g/mol"". That is the molar mass of sulfate of aluminum is 342 g/mol.
6. Molar and usual masses is interconnected by a formula: m =? * M where m is the usual weight expressed in grams? - amount of substance in moths, M - molar weight in g/mol. Increase molar weight by number of moles and receive the mass of substance. So, 1 mol of sulfate of aluminum weighs 342 grams, 2 asking - 684 grams, etc.
7. If you know amount of substance in moths and its usual weight, then molar weight calculate by formula M = m/?.