3. quantitative chemistry

• Compounds have a relative formula mass, M, which is the sum of the relative atomic masses of all the atoms in the molecular formula.
• The relative atomic masses of all the elements in the compound can be found on the periodic table.
• The relative formula mass of MgCl, for example, is 95, which is calculated by adding up the relative atomic masses of Mg and Cl.
• There are two chlorine atoms in MgCl, so the relative atomic mass of chlorine needs to be multiplied by 2.
• The percentage mass of an element in a compound can be calculated by finding the number of atoms of that element in the compound and multiplying it by the relative atomic mass of the element.
• The percentage mass of sodium in sodium carbonate, Na,CO3, for example, is 43%, calculated by finding the number of atoms of sodium, carbon, and oxygen in the compound and multiplying it by their relative atomic masses.
• The mass of iron in a mixture containing 20% iron ions by mass can be found by subtracting the percentage mass of iron in iron chloride from 100%.
• The percentage mass of iron in iron chloride is calculated by finding the mass of iron in the mixture and dividing it by the mass of iron chloride.
• The mass of iron chloride that contains 10 g of iron can be found by subtracting the percentage mass of iron in iron chloride from 100%.