Summary Chemistry vwo 3 “chemical calculations”

Summary ‘chemical calculations’

1.1 How much of a substance do you have?
 When you want to indicate how much you have of a substance use quantities
 How heavy -> weight or mass -> kg
 How big -> volume -> L
 How many -> number -> 20

1.2 mass
 We use weight to indicate how heavy something is
 Weight is determined by gravity
 Mass will stay the same therefore in science we use mass which is measured with a balance
 The standard unit for mass is kg




1.3 volume
 Volume -> amount of space taken up by a substance
 We often use litre (L) and millilitre (mL)
 The standard unit for volume is m³




1.4 density
 A substance can have any mass or volume they are not characteristic properties
 But Density is a characteristic property
 It doesn’t change with the amount of a substance you have




 Unit for density is kg/m3 and sometimes g/L

1.5 calculations with density
 When you need to convert mass to volume or vice versa:

,  Density of iron is 7870 which becomes 7.87 x 10³ kg/m³
 1 Ml = 1 cm³-> dm³ -> m³ (-6 steps)
 12 ml = 12 x 10(-6)
 M = 12 x 7.87 = ³– 10(6) = 10-³
 M = 94 x 10-³
 Mg – cg – dg – g – dag – hg – kg
 94 x 10-³ kg = 94 x 10³ mg (kg -> mg = +6 steps)

2.1 atomic mass
 Kg is the standard unit of mass
 The mass of one atom is very small so a different unit is used
 The atomic and molecular mass unit is used -> u




 The symbol of atomic mass is A
 ^ atomic mass of aluminium

2.2 molecular mass
 Molecular mass -> the mass of a molecule expressed in u
 The mass can be calculated by adding up the masses of all atoms in the molecule using the
atomic masses
 Symbol for molecular mass is M




2.3 mass percentage in compounds
 Mass percentage -> mass of the element as a percentage of the total mass of the compound