TOPIC 1; Stoichiometric Relationships
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Kinetic-molecular theory
describes the differences in the properties of solids, liquids, and gases on the basis of the different kinetic energies of the particles.
• The molar mass (M)
• The molar mass (M) is the relative mass expressed in g and has units of g mol–1.
relative atomic mass (Ar)
relative atomic mass (Ar) of an element is the average mass of an atom according to relative abundances of its isotopes, on a scale where the mass of one atom of 6 12C is 12 exactly. It has no units.
relative molecular mass (Mr)
is the sum of the relative atomic masses of the atoms in the molecular formula.
Titration
Titration is a chemical technique in which one solution is used to analyse another solution to find its concentration or amount.
Concentration
Concentration is the amount of solute in a known volume of solution. It can be expressed either in g dm–3 or mol dm–3. Concentration in mol dm−3 is often represented by square brackets around the substance: [solute] (mol dm−3) = nsolute (mol)/Vsolution (dm3)
• Density
mass/volume
A solution
• A solution is a homogeneous mixture of a liquid (the solvent) with another substance (the solute). The solute can be solid, liquid, or gas but the solvent is generally a liquid.
STP
STP for gases is standard temperature (0 °C or 273 K) and pressure (100 kPa).
Number of mol
= volume/molar volume
Avogadro’s law
Avogadro’s law states that equal volumes of different gases contain equal numbers of particles at the same temperature and pressure.
Temperature
Temperature (in K) is a measure of the average kinetic energy of the particles. Particles have minimum kinetic energy at absolute zero (0 K).
The ideal gas equation:
PV = nRT • R = 8.31 J K–1 mol–1, T must be in K. • T in k (C + 273)
Percentage yield
(experimental yield/theoretical yield) × 100%
SL unit of temperature
The kelvin is the SI unit of temperature: T (K) = T (°C) + 273
fixed mass of an ideal gas at constant T
P = k1/V (k1 constant)
Compounds
Compounds contain a fixed ratio of atoms of different elements and have different properties from their component elements.
Mixtures
Mixtures contain more than one element or compound that are not chemically combined.
The molar mass (M)
is the relative mass expressed in g and has units of g mol–1.
Number of mol
= mass/molar mass: n = m/M
Number of particles
Number of particles = number of mol × Avogadro’s constant: N = nL