To find amount of atoms in substance, define what substance is. Then find its weight and molar weight. Then increase the relation of weight and molar weight by Avogadro's number which is equal to 6.022*1023.
It is required to you
- For determination of amount of atoms in substance take exact scales (lever or electronic), Mendeleyev's table, the manometer, the thermometer.
Instruction
1. Determination of amount of atoms in pure substance Weigh a sample of the studied substance on exact scales, receive result in grams. Make sure that it consists of one-atomic molecules. Then, using Mendeleyev's table, find the molar mass of the studied substance expressed in grams on mol. For this purpose find the element corresponding to substance of which the body consists and write down its molecular weight. It will also be equal to the molar weight expressed in grams on mol. For example, for iron (Fe) it is 55.845 g/mol. If isotope, for example iron 55 is precisely known, then it is possible to take an integer, however, pure isotopes often are radioactive. Then divide the mass of substance into its molar weight, and increase result on 6.022*10^23. It will also be amount of atoms in this mass of substance.
2. The amount of atoms in complex substance If substance consists of polyatomic molecules, for example, water which molecule consists of one atom of oxygen and two atoms of hydrogen, make the following sequence of actions. By means of scales find the mass of a sample. Then write down its chemical formula, and by means of Mendeleyev's table find the molar mass of each of atoms of which the molecule consists. In a case with water it will be hydrogen – 1 gram on mol, and oxygen – 16 grams on mol. As hydrogen 2 atoms, increase molar weight by this number, as a result receive the general molar weight of 18 grams on mol. Then we divide weight in grams into molar weight in grams on mol and we multiply on 6.022*10^23. The quantity of molecules in substance will be result, increase this number by amount of atoms in one molecule (for water it equally to 3).
3. The amount of atoms in mixes and splavakhesl substance represents mix of several substances with the known mass fractions, measure its lump. Then find the mass of pure substances, having increased weight by respective shares. For example, if bronze contains 70% of copper and 30% of tin, but for obtaining mass of copper increase the mass of a sample by 0.7, and for obtaining mass of tin you will increase the mass of a sample by 0.3. Further act as it is described in the previous points.
4. The amount of atoms in gas If gas is in normal conditions (pressure of 760 mm Hg. and temperature 00C), determine the volume of this gas by geometrical methods (for example to find gas volume in the room representing a parallelepiped multiply length, width and height), having expressed it in cubic meters. Divide the received number into 0.0224 and increase on 6.022*10^23. If a gas molecule diatomic, increase result by 2. If pressure, volume and temperature of gas (pressure is measured by the manometer, and temperature the thermometer), then find the work of pressure in Pascals upon volume in cubic meters are known, divide into value of temperature in Kelvins, and number 8.31. Increase the received result on 6.022*10^23 and amount of atoms in a gas molecule.