Acids, bases and salt preparations trpl content

Question 1

describe an experiment to prepare a pure, dry sample of a soluble salt,
starting from an acid and alkali

Answer 1

Use a pipette to measure the alkali into a conical flask and add a few drops of indicator (phenolphthalein or methyl orange)

Add the acid into the burette and note the starting volume

Add the acid very slowly from the burette to the conical flask until the indicator changes to appropriate colour

Note and record the final volume of acid in burette and calculate the volume of acid added (starting volume of acid - final volume of acid)

Add this same volume of acid into the same volume of alkali without the indicator

Heat to partially evaporate, leaving a saturated solution

Leave to crystallise decant excess solution and allow crystals to dry

Question 2

describe an experiment to prepare a pure, dry sample of an insoluble salt,
starting from two soluble reactants

Answer 2

The method involves measuring out a fixed volume of one salt solution and then adding the second salt solution until it is in a slight excess

This ensures the maximum amount of precipitate will be obtained

The precipitate is recovered by filtration

Then it must be washed with distilled water remove reactants that are contaminating the residue (recovered solid)

It is then left to dry

Question 3

Practical: Prepare Lead(II) Sulfate

Answer 3

Measure out 25 cm3 of 0.5 mol dm3 lead(II)nitrate solution and add it to a small beaker

Measure out 25 cm3 of 0.5 mol dm3 of potassium sulfate add it to the beaker and mix together using a stirring rod

Filter to remove precipitate from mixture

Wash filtrate with distilled water to remove traces of other solutions

Leave in an oven to dry

Soluble salt 1 = lead(II) nitrate

Soluble salt 2 = potassium sulfate