Chemistry
Chemistry
The Basics
1. Moles
Number of moles = mass (molecular covalent compounds)
Molecular mass
Number of moles = mass (ionic compounds)
Formula mass
Number of moles = mass (elements)
AR
2. Concentration
Concentration = number of moles
Volume (litres)
C = n moll-1
V
3. Volumes of Gases
Volume of gas = No of moles x Volume (1 mole of ideal gas)
V = n x V(mol of ideal gas @ SLC or STP)
4. Valencies
The valency of valence of an element or compound is a measure of its combining power when it takes part in a chemical reaction.
In general the valency of an element relates to it Group number in the periodic Table, i.e
- Sodium is in Group 1 and has a valency of +1.
- Magnesium is in-group 2 and has a valency of +2.
- Chlorine is in Group 7 and has a valency of –1.
Exceptions to this rule are the multi-valent elements:
|Element |Valencies |
|Copper |Cu+ ; Cu2+ |
|Iron |Fe2+ ; Fe3+ |
|Lead |Pb2+ ; Pb4+ |
|Tin |Sn2+ ; Sn4+ |
|Mercury |Hg+ ; Hg2+ |
|Silver |Ag+ |
|Zinc |Zn2+ |
Polyatomic Ions
Cations:
Ammonium - NH4+
Anions
|Polyatomic Anion |Formula |
|Sulfate |SO42- |
|Sulfite |SO32- |
|Nitrate |NO3- |
|Nitrite |NO2- |
|Carbonate |CO32- |
|Hydroxide |OH- |
|Phosphate |PO43- |
Note: The ending –ide refers the anion being and element only, (the exception being Hydroxide).
Ionic Compounds:
Ionic compounds are named by putting the cation first, followed by the anion. For example:
Sodium Chloride, NaCl
Magnesium Carbonate, MgCO3
Note: When ionic compounds for they must be electrically neutral.
General Reaction Equations
1. Neutralisation
acid + alkali ( metal salt + water
example
HCl + NaOH ( NaCl + H2O
2. Metal + acid
metal + acid ( metal salt + hydrogen
example
Mg + H2SO4 ( MgSO4 + H2
3. Metal carbonate + acid
metal carbonate + acid ( metal salt + carbon dioxide + water
example
MgCO3 + H2SO4 ( MgSO4 + CO2 + H2O
Enthalpy
q = -mC∆T J
∆H = q x 1 kJmol-1
1000 x n
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