Thus, 100 cm 3 of CO 2 are equivalent to 1 2240 × 100 moles of CO 2 Thus, 22400 cm 3 of CO 2 are equivalent to 1 mole of CO 2.Īnd 1 cm 3 of CO 2 is equivalent to 1 22400 moles of CO 2. Use is made of the above definition that at 101.3 kPa and 273 K, 22400 cm 3 of any gas is the volume of 1 mole of the gas. For example, to find the number of moles of carbon dioxide gas which are contained in 100 cm 3 of the gas measured at 273 K and 101.3 kPa.
Using the molar volume definition, if the volume of a gas is known, the number of moles and hence the mass of the gas can be determined. Volumes of gases are easier to measure than masses. When applied to gases, the molar volume of any gas is defined as occupying 22.4 dm 3 at a temperature of 273 K and pressure 101.3 kPa (atmospheric pressure). That is, the mass of sodium hydroxide required is 16 g. Mass of NaOH = number of moles × relative molecular of NaOH mass of NaOH In order to find the mass of sodium hydroxide required to make 200 cm 3 of 2 M solution:Ģ00 cm 3 of a 2 M solution requi× 200 moles.Ġ.4 moles of NaOH has a mass found by the equation: That is, the number of moles of sodium hydroxide is 0.4. Thus, 1 cm 3 of the solution contamoles of NaOH and 200 cm 3 of the solution conta× 200 moles of NaOH. For example, to find how many moles of sodium hydroxide, NaOH, are contained in 200 cm 3 of a 2 M, (2 molar), solution:ġ000 cm 3 of the solution contains 2 moles of NaOH This means that if the concentration of the solution is known in moles per dm 3, the number of moles in any volume of solution can be determined. When applied to solutions, a 1 molar, (1 M), solution is one in which 1 mole of a solute is dissolved in a solvent in order that the volume of the solution is 1000 cm 3 ( 1 dm 3 or 1 litre). For many purposes the relative atomic masses are rounded up to the nearest whole number except for chlorine and copper which are 35.5 and 63.5 respectively. For example, calcium carbonate contains calcium, carbon and oxygen in the ratio 1:1, 3 (i.e. When applied to molecules, one mole of molecules is the relative molecular mass of that molecule, which is the summation of the individual relative atomic masses of the constituent atoms. Thus, one mole of sodium weighs 23.0 g or one tenth of a mole of sodium weighs 2.3 g. Using the chemical formula of the compound and the periodic table of elements, we can add up the atomic weights and calculate molecular weight of the substance.The word ‘mole’ has been adopted to represent the Avogadro number of atoms of an element, that is, the relative atomic mass of an element.
For bulk stoichiometric calculations, we are usually determining molar mass, which may also be called standard atomic weight or average atomic mass. This is not the same as molecular mass, which is the mass of a single molecule of well-defined isotopes.
#Oxygen atomic mass how to#
This is how to calculate molar mass (average molecular weight), which is based on isotropically weighted averages. The atomic weights used on this site come from NIST, the National Institute of Standards and Technology. The percentage by weight of any atom or group of atoms in a compound can be computed by dividing the total weight of the atom (or group of atoms) in the formula by the formula weight and multiplying by 100. If the formula used in calculating molar mass is the molecular formula, the formula weight computed is the molecular weight. This site explains how to find molar mass. The reason is that the molar mass of the substance affects the conversion. To complete this calculation, you have to know what substance you are trying to convert. These relative weights computed from the chemical equation are sometimes called equation weights.Ī common request on this site is to convert grams to moles. The formula weight is simply the weight in atomic mass units of all the atoms in a given formula.įormula weights are especially useful in determining the relative weights of reagents and products in a chemical reaction. When calculating molecular weight of a chemical compound, it tells us how many grams are in one mole of that substance. In chemistry, the formula weight is a quantity computed by multiplying the atomic weight (in atomic mass units) of each element in a chemical formula by the number of atoms of that element present in the formula, then adding all of these products together.įinding molar mass starts with units of grams per mole (g/mol).