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TOPIC: STOICHIOMETRY
- S.I. UNIT OF QUANTITIES: LENGTH, MASS VOLUME ETC
- BASIC CONCEPTS: MOLE, MOLAR QUANTITIES, MOLALITY, STANDARD TEMPERATURE AND PRESSURE (S.T.P.)
- CALCULATIONS INVOLVING MASS AND VOLUME
- MORE CALCULATIONS ON MASS AND VOLUME RELATIONSHIP.
PERIOD 1: S.I. UNIT OF QUANTITIES: LENGTH, MASS VOLUME ETC
S.I. UNITS OF QUANTITIES.
S.I. unit means international system [used to describe units of measurements from French ‘system international’] S.I. units
For example
| QUANTITY | SYMBOL | UNITS |
| Length | L | m, cm |
| Mass | M | g or kg |
| Molar mass | M | gmol-1 |
| Volume | V | cm3, dm3 |
| Amount | N | mol |
| Molar concentration | L | mol.dm-3 |
| Mass concentration | P | gdm-3 |
| Avogadro’s law | L | mol-1 |
| Avogadro’s number | N | —— |
| N.B molar mass | M | g.mol-1 |
Relationship between quantities
(a) M = i.e molar mass =
Molar volume =
(b) Molar volume = =
(c) Avogadro’s constant = L = ==
TYPES OF MASS AND VOLUME PROBLEMS
There are two types of mass and volume relationship problems namely:
- Mass- mass problem:
In this type of problem, the reacting mass of substance and its molar mass is usually given and we may be required to determine the mass of another substance produced and its molar mass also given. The reversed form of this is when the mass of another substance product produced is given and one is asked to find the mass of the substance which produced it.
- Mass- gas volume problem:
In this case, you may be given a certain reacting mass of a reactant and required to find the volume of another substance produced at S.T.P. or under any other conditions. The reverse of this type is when you are given the volume of a certain gas liberated at S.T.P or other conditions and the gas produced.
Note: This method is related to simple proportion as in mathematics.
- Gas volume – gas volume problem
In this class of reactions, only the volumes of the reactants and products are involved in the calculations.
- Mass – Liquid volume problem
In this type, the mass I given and the volume of liquid has to be determined.
- Liquid volume – volume problem
In this group of calculations, one volume is given while another is to be found.
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