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Difficulty: MediumTypes and Preparation Methods of Salts

Complete the following statement regarding laboratory methods of salt preparation and salt classification.

Answer:The preparation of anhydrous iron(III) chloride (FeCl3FeCl_3) by reacting red-hot iron filings directly with dry chlorine gas is an example of 【direct combination】, whereas potash alum, KAl(SO4)2⋅12H2OKAl(SO_4)_2 \cdot 12H_2O, is classified as a 【double】 salt.

Answer

The preparation method is direct combination (or synthesis), and potash alum is classified as a double salt.
Anhydrous binary salts like iron(III) chloride must be synthesized by direct combination of their elements in dry conditions to avoid hydrolysis. Potash alum is formed by equimolar crystallization of potassium sulfate and aluminium sulfate, yielding a double salt.

Step-by-Step Solution

1
Determine the preparation method for anhydrous iron(III) chloride.
Direct combination of elements (2Fe(s)+3Cl2(g)→2FeCl3(s)2Fe_{(s)} + 3Cl_{2(g)} \rightarrow 2FeCl_{3(s)}) is used because aqueous crystallization causes salt hydrolysis.
Reacting two elements directly to form a compound without water is direct combination/synthesis.
2
Classify potash alum based on its chemical formula and ionic behavior.
Potash alum contains two distinct metallic cations (K+K^+ and Al3+Al^{3+}) combined with sulfate anions (SO42−SO_4^{2-}), making it a double salt.
Salts composed of two simple salts crystallized together in equimolar proportions that dissociate completely into constituent ions are double salts.

Key Concept

Salt Preparation Methods and Classifications
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Topics

Types and Preparation Methods of Salts

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