Qualitative Analysis

Sometimes we need to identify what substance we have from its property. That reason makes us have to know the properties of chemical substances around us. Here are some examples of qualitative analysis data from Cambridge International Examination Chemistry A Level.
From the table, we can conclude that there are differences when we react the cations with strong or weak base. For example is: Aluminium.
Al3+(aq) + 3OH-(aq) <--> Al(OH)3(s)
In excess of NaOH, aluminium will form [Al(OH)4]- that reduces the concentration of hydroxide and make the equilibrium shifts to left so that the precipitate soluble in excess.
Meanwhile, in excess of NH3, aluminium won’t form the complex compound. The excess will shift the equilibrium to right so that there are more precipitate formed.

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