The mass of substance is by means of the device which is called scales. It is also possible to calculate body weight if the amount of substance and its molar weight or its density and volume is known. The amount of pure substance is possible find on its mass or quantity of molecules which contains in it.
It is required to you
- - scales;
- - table of density;
- - periodic table of elements.
Instruction
1. To find body weight put it on scales and perform measurements. In lever scales the body weight will need to be counterbalanced with a special counterbalance, and in electronic just put a body on the special platform. Medical determine body weight on lever scales of type by a special scale, and at equal shoulders of the lever (like pharmaceutical), by the mass of a counterbalance.
2. If it is not possible to weigh substance on scales, calculate its weight through density. For this purpose find substance volume. Measure its linear sizes and make calculation. According to the special table find density of this substance. Find its weight m how the work of density? on the volume of V (m=? • V). For example, if in the room of 6х8х3 meters in size there is an air at a temperature of 20? With, find its weight having counted the room volume (gas occupies all volume provided to it) V=6•8•3=144 m?. After that increase result by air density for this temperature it is equal to 1.2 kg/m?, kg m=1.2•144=172.8.
3. For determination of mass of pure substance learn its chemical formula. By means of the periodic table of elements find its molar weight. For this purpose put the mass of all elements entering a formula. The received number will be to equally molar mass of substance in grams on mol. To find the mass of m, increase molar weight M on quantity substances? (m=? • M). Receive weight in grams.
4. If the mass of substance is known, determine molar weight by the periodic table and find amount of substance. For this purpose the mass of substance in m grams, divide M into its molar weight (? =m/M). Receive result in moths. For example, if 108 grams of water are taken, then its amount of substance will be? =108/18 = 6 mol, where 18 g/mol – the molar mass of water.
5. If the number of molecules of substance is known, but find amount of substance, using Avogadro's number of NA=6,022•10^23 1/mol (quantity of molecules of substance in 1 pier). To find amount of substance divide number of molecules N into Avogadro's number of NA (? = N/NA).