Formulae
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Relative Isotopic Mass Mass of 1 atom of an isotope of an element / 1/12 the mass of 1 atom of carbon-12 isotope
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Relative Atomic Mass Avg mass of 1 atom of an element / 1/12 the mass of 1 atom of carbon-12 isotope
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Relative Molecular/Formula Mass Avg mass of 1 molecule/formula unit of a substance / 1/12 the mass of 1 atom of carbon-12 isotope
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Mr Sum of Ar of atoms in the molecular formula
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Empirical Formula Simplest formula which shows ratio of atoms of different elements in the compound
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Molecular Formula Formula which shows actual number of atoms of each element in one molecule of the compound
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Relative formula mass is used for ionic compounds
Relative masses have no units as they are ratios of 2 masses
Calculations using Volume of Gases
Avogadro's Law:
Equal volume of all gases, under the same temperature and pressure, contain the same number of particles (atoms or molecules)
Gases in a balanced equation: Volume ratio = Mole ratio
Molar Volume, Vm:
Volume occupied by 1 mole of the gas at a specific T&P
Standard T&P : 273K (0 degree celsius), 1 bar (100 kPa), 22.7dm^3/mol
Room T&P: 293K (20 degree celsius), 1 atm (101 kPa), 24 dm^3/mol |
Volumes of gases are dependent on T&P hence these conditions must be specified
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Stoichiometry
Stoichiometry: Quantitative aspects of chemical formulae & reactions
Limiting reactants are completely consumed in the reaction and limit how much products can form.
Percentage Yield =
Actual yield/mass or amount of product formed /
Theoretical yield/mass or amount of product formed
x 100% |
Types of Reactions
Precipitation Reaction |
Reactions which involve formation of insoluble solid (ppt) from reaction of 2 solutions |
Types of Reactions
Precipitation Reaction |
Reactions which involve formation of insoluble solid (ppt) from reaction of 2 solutions, Separation by filtration or decanting |
Thermal Decomposition |
Chemical reaction caused by heat, Compounds break down into 2 or more substances |
Acid-Base |
Elaboration in a later segment |
Redox |
Elaboration in a later segment |
Calculations using Concentrations
When a solute is dissolved in a solvent, a solution is formed
If the solvent is water, an aqueous solution is formed
The concentration of a solution (mol dm^-3) shows the amt of solute dissolved in a given volume of solution
Standard solution: Solution whose concentration is accurately known
[X] - Amt of X (mol) / V of solution (dm^3)
No of moles of solute, n:
- [solute] (mol dm-3) X Volume (dm3)
- Mass of X (g) / Molar mass of X (g/mol)
When a solution is diluted (by adding more solvent), the concentration of the solution decreases but no. of moles of solute in the diluted solution remains unchanged |
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Acid-Base Reactions
Arrhenius Theory of Acids & Bases
- An acid is a substance that dissociates in water to produce H3O+(aq)
- A base is a substance that dissociates in water to produce OH- (aq)
Neutralisation: H+ (aq) + OH-(aq) -> H2O (l)
Limitation: Aqueous solutions only
Bronsted-Lowry Theory of Acids & Bases
- An acid is defined as any species which donates a proton, H+. It must thus contain Hi n its formula
- A base is defined as any species which accepts a proton, H+. It must contain a lone pair of electrons to bind the H+ ions
Bronsted-Lowry acid-base reaction involves the transfer of a proton from an acid to a base. They do no occur only in aq solutions but also between gases and non-aq systems.
Limitation: Does not address why substances such as BF3 or AlCl3 do not contain any H atom but are known to behave as acids
Lewis Theory of Acid & Bases
- An acid is a species that accepts an electron pair, e.g. BF3
- A base is a species that donates an electron pair, e.g. NH3
Lewis acid-base reaction can be viewed as a transfer of a pair of electrons from the base to the acid
Limitation: Too general
The 3 models can be used to interpret different acid-base systems
BL and L theories - Describe specific acid-base reactions
Arr theory - Whether isolated substances are acids, bases, or neither |
In aqueous solution, H+ does not exist on its own. It forms a dative bond with a water molecule to form H3O+, called hydronium or hydroxonium ion. Chemists often use H+ and H3O+ interchangeably o refer to the elevated H+ ion.
Best to use Bronsted-Lowry theory wherever possible for an acid-base reaction, and apply Lewis theory only when reaction does not involve proton transfer
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Redox Reactions
Redox Reaction |
Reaction that involves reduction and oxidation simultaneously |
Reduction |
Process whereby a substance gains electrons, resulting in a decrease in OSN |
Oxidation |
Process whereby a substance loses electrons, resulting in an increase in OSN |
Reducing agent (reductant) |
Substance that gives electrons to another, itself being oxidised in the process |
Oxidising agent (oxidant) |
Substance that takes in electrons from another, itself being reduced in the process |
Disproportionation |
Redox reaction in which the same substance is both oxidised and reduced |
Oxidation Number (OSN) |
Number of electrons to be added or subtracted from an atom in a combined state to convert it to elemental form |
Acronym: OIL RIG
When writing the OSN, +/- signs must be stated before the number
Balancing Redox Reactions
Method 1
1. Balance elements that were oxidised or reduced
2. Balance O with H2O
3. Balance H with H+
4. Balance charges with electrons
Method 2
1. Balance elements that were oxidised or reduced
2. Add electrons (OSN x No of that element)
3. Balance O with H2O
4. Balance H with H+
Method 3
1. Balance elements that were oxidised or reduced
2. Electrons gained = Electrons lost
- a x 7e = b x 2 x 1e
- Same on LHS and RHS, figure out what a and b are, multiply the relevant coefficients
3. Balance O with H2O
4. Balance H with H+ |
Balancing Redox Reactions
Method 1
1. Balance elements that were oxidised or reduced
2. Balance O with H2O
3. Balance H with H+
4. Balance charges with electrons
Method 2
1. Balance elements that were oxidised or reduced
2. Add electrons (OSN x No of that element)
3. Balance O with H2O
4. Balance H with H+
Method 3
1. Balance elements that were oxidised or reduced
2. Electrons gained = Electrons lost
- a x 7e = b x 2 x 1e
- Same on LHS and RHS, figure out what a and b are, multiply the relevant coefficients
3. Balance O with H2O
4. Balance H with H+ |
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