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Module 1: Análisis volumétrico

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XSIQ
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Chemistry - Standard solutions

Standard solutions

Volumetric analysis via titration requires that the concentration of one
of the solutions used be accurately known. Such a solution is known as a
standard solution.

Standard solutions can be prepared from solids known as primary standards.

Anhydrous Na2CO3 qualifies as a primary standard because it:

* is readily available in a highly purified form

* has a known formula

* will not react with the atmosphere

* is inexpensive

* has a relatively high molar mass (106 g mol), thus minimising the
effect of minor weighing errors

Sodium hydroxide is not a primary standard because:

* it absorbs water from the atmosphere

* it reacts with atmospheric CO2

* it has a low molar mass (40)

Consequently the concentration of an aqueous solution of NaOH cannot be
accurately determined from the m(NaOH) used to produce the solution. Its
concentration must be determined, ie the solution standardised by titration
with an acid of known concentration.

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