GCSE Chemistry Unit 2.6- Acids, Bases and Salts

What is an insoluble base?

A metal oxide or hydroxide ( these are alkalis)

What is a reversible reaction?

A reversible reaction is exothermic in one direction, and endothermic in the other. The heat transfers are the same.

What is crystallisation?

After you have filtered out either the metal, metal oxide or metal hydroxide, evaporate some of the water ( to make the solution more concentrated) and then leave the rest to evaporate slowly to get pure crystals.

Ammonia

Ammonia dissolves in water to make an alkaline solution. Ammonium salts are important as fertilisers because ammonium nitrate has nitrogen from 2 sources; ammonia and nitric acid, and plants need nitrogen to make proteins.

What is an endothermic reaction? Give examples

An endothermic reaction is where energy is taken in from the surroundings. Examples: Thermal decompositions, sports injury packs ( that take in heat so the pack becomes cold)

What is an exothermic reaction? Give examples

An exothermic reaction is where energy is transferred to the surroundings. Examples: Combustion, oxidation, neutralisation, hand warmers ( through oxidation of iron in air) and self-heating cans.

How can soluble salts be made from acids?

By reacting them with: Metals- although some are too reactive or unreactive Insoluble bases- this is added to the acid until it no longer reacts and the excess solid is filtered off. Alkalis- an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution.

Hydrochloric acid will produce: Sulfuric acid will produce: Nitric acid will produce:

Chloride salts sulfate salts nitrate salts

What happens when chemical reactions occur?

Energy is transferred to or from the surroundings.

Acids form: Alkalis form:

Hydrogen atoms with a positive charge Hydroxide atoms with a negative charge These react together to produce water.

What happens during the thermal decomposition of hydrated copper sulfate?

If you HEAT blue hydrated copper sulfate crystals, it leaves WHITE ANHYDROUS copper sulfate powder and separates it from the water. ( Endothermic.) If you then add water you get the crystals back (exothermic.)

What is the difference between making a soluble salt with an insoluble or soluble base?

Nothing, but with soluble bases like sodium, potassium or ammonium hydroxides you can't tell whether the reaction's finished so you must use a universal indicator ( a dye) that will go green if the solution is neutral.

What does an acid and a metal produce?

Salt and hydrogen

What does an acid and a base produce?

Salt and water

The salt produced in any reaction depends on

The acid used the metal in the base or alkali

Making insoluble salts

Use a precipitation reaction. This is where you pick the two solutions that contain the ions you need. Once the salt has precipitated out, wash it and dry it on filter paper. These reactions can be used to remove poisonous ions from drinking water or for treating effluent.

What is neutralisation?

neutralisation is where an acid( a substance with a Ph less than seven) reacts with a base (a substance with a ph greater than seven.) Their products are neutral ( have a Ph of seven.)