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Summary Chemistry vwo 3 “chemical calculations”
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Summary Chemistry vwo 3 “chemical calculations”
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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
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