ACDS, BASES AND SALT PREPARATIONS - CHEMISTRY

ALWAYS SOLUBLE

• Na+

• K+

• NH4+

• NO3-

MOSTLY SOLUBLE

• Cl-, except AgCl and PbCl2

• SO4 2-, except BaSO4, CaSO4, PbSO4

MOSTLY INSOLUBLE

• CO3 2-, except SPA salts

• OH-, except Na+, K+, Ca2+

What is an acid

A proton donor

What is an alkali

A soluble base which is a proton acceptor

Acid + base

Acid + base → salt + water

Acid + metal

Acid + metal → salt + hydrogen

Acid + metal oxide

Acid + metal oxide → salt + water

Acid + metal hydroxide

Acid + metal hydroxide → salt + water

Acid + metal carbonate

Acid + metal carbonate → salt + CO2 + H2O (effervescence)

How to prepare a pure dry sample of a soluble salt from an insoluble reactant and an acid

• Heat the acid in a water bath in a fume cupboard

• Add the base to the acid until it is in excess (the excess solid will sink to the bottom of the flask

• Filter offf the excess solid to get a solution containing only the salt and water

• Heat the solution gently to evaporate off some of the water

• Leave the solution to cool and allow the salt to crystallise

• Decant the solution twice to wash of impurities then pat dry

How to prepare a pure, dry sample of a soluble salt from an acid and alkali

• first carry out a titration to determine the exact amounts of alkali needed to neutralise the acid

• Measure out a set amount of acid into a conical flask using a Pipette

• Add a few drops of indicator

• Slowly add the alkali to the acid. Regularly swirl the conical flask until there is a colour change

• Then carry out the reaction using exactly the same volumes of alkali and acid but with no indicator

• The solution that remains contains only the salt and water

• Slowly evaporate off some of the water then leave the solution to crystallise.

• decant it twice then pat dry

How to prepare a pure dry sample of an insoluble salt starting from two soluble reactants

• precipitation reaction

• Add a fixed volume of one salt solution and then add the second salt solution in excess

• Then filter the mixture

• Wash the residue twice with distilled water

• Leave to dry in warm oven

Practical: prepare a sample of pure, dry, hydrated copper Sulfate crystals starting from copper oxide.

• add 50cm³ of dilute sulfuric acid into a beaker and warm it gently

• Add copper oxide slowly and stir until the base is in excess

• Filter the mixture using funnel and filter paper

• Place the filtrate into an evaporating basin and evaporate water from solution until crystals form

• Leave basin by window or in warm oven to dry

• Wash the crystals twice and pat dry

PRACTICAL: prepare a sample of pure, dry lead(II) Sulfate

• add 1 spatula of lead nitrate to a test tube. Dissolve it in deionised water.

• Shake the test tube thoroughly

• In a separate tube do the same with 1 spatula of magnesium Sulfate

• Tip the two solutions into a small beaker and stir.

• Use filter paper and a funnel to filter the contents of the beaker into a conical flask

• Pour more water into the beaker to make sure all the precipitate is in the filter paper

• Rinse the residue twice with deionised water to make sure all magnesium nitrate has been washed away

• Lead the lead Sulfate to dry in an oven or near a window