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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