CSEC Chemistry Paper 2
Acids, Bases & Salts-Salt Preparation (Teaser??)
Since we know that when an acid and a base react, a salt and water is formed, we automatically know how to make at least one salt, provided we know an acid and a base.
In preparing a salt, any salt, the type of salt being made has a lot to do with the method employed. Type here could be anhydrous or hydrated, soluble or insoluble or described based on type of cation present in the salt.
If the salt is an anhydrous chloride like iron (II) chloride, for example, we would go the route of direct combination where the metal would be heated in dry chlorine in a tube (all theoretical as I’ve never prepared this one, nor is it popularly prepared in your school lab. A little theory doesn’t hurt though)
Fe(s) + Cl2(g) –>FeCl2(s)
The next step in what we would learn depends on what we think comes first, the chicken or the egg. (I say the chicken)
If it is not an anhydrous salt, then the matter of solubility comes into play. Before asking if the salt is soluble or not, we would need to know the rules or guidelines to follow where *solubility of salts is concerned.
They are (and are not exhaustive but will cover most of the salts we will cover in the CSEC syllabus)
• All sodium, potassium and ammonium salts are soluble.
• All nitrates are soluble
• All chlorides are soluble except lead and silver (lead chloride is soluble in hot water)
• All sulphates are soluble expect calcium, barium and lead (many texts will cite calcium sulphate as being “sparingly” or “moderately” soluble.
• All carbonates are insoluble (with exception of potassium, sodium and ammonium)
Though not salts, the following makes the learning complete:
• The hydroxides of sodium, potassium, and ammonium are very soluble in water. The hydroxides of calcium and barium are moderately soluble. The oxides and hydroxides of all other metals are insoluble.
* Solubility can be taken as the measure or extent to which a substance will dissolve in water (under standard conditions.)
Come up with a simple mnemonic to assist with remembering the rules given above.
Today is a light day. We will make things more “solid” when we review how to make an insoluble salt.
Contributed by: Kemil Walford