1.2 Amounts of Substance Flashcards
Relative atomic mass (Ar)
The weighted average mass of all the isotopes of an element relative to 1/12th the mass of an atom of carbon-12
Relative molecular mass (Mr)
The mass of a molecule of the compound relative to 1/12th the mass of an atom of carbon-12
What is relative formula mass used for?
Ionic compounds
What is relative molecular mass used for?
Covalent substances
Relative formula mass (Mr)
The mass of one formula unit of an ionic compound relative to 1/12th the mass of an atom of carbon-12
A mole
The amount of substance that contains as many particles as there are in exactly 12g of carbon-12
What is the symbol for the Avagadro Constant?
L
What are the units of the Avagadro constant?
Mol⁻¹
What is the mass of one mole of a substance?
It’s Mr in grams.
E.g. 1 mole of carbon = 12.0g
Conversion of mg to g
×10⁻³
Conversion of kg to g
×10³
Conversion of tonnes to g
×10⁶
Conversion of cm³ to dm³
×10⁻³
Equation for number of moles
Mass (in g) / Mr
Equation for number of atoms
n (moles) x L (Avogadro’s constant)
Equation for concentration
n (moles) / volume (dm³)
Ideal gas equation
PV = nRT
Units used for the ideal gas equation
P = Pa
V = m³
n = mol
R = JK⁻¹mol⁻¹
T = Kelvin
Empirical formula
The simplest whole number ratio of atoms of each element in a compound
Molecular formula
The actual number of atoms of each element present in a molecule
Conversion from degrees C to Kelvin
+273
What are the units of molar mass?
g mol⁻¹
What 2 assumptions are made when using the ideal gas equation?
- No intermolecular forces between molecules
- Volume occupied by molecules in negligible relative to the volume of the container
What are two acid-base indicators?
Methyl orange
Phenolphthalein
Percentage error
(Uncertainty / value) ×100
Methyl orange colour in acid
Red
Methyl orange colour in base
Yellow
Phenolphthalein colour in acid
Colourless
Phenolphthalein colour in base
Pink
Atom econemy
(Molecular mass (Mr) of desired product/sum of molecular masses of all products) ×100
Reasons for low percentage yeild
- Incompleate/reversible reactions
- Side reactions
- Mechanical losses
- Impurities in the reactants
What is a back titration?
A titration used for substances that are insoluble in water. They are instead reacted with acid to form a solution.
Water of crystallisation
The water molecules that form an essential part of the crystalline structure of a hydrated salt
