making crystals

Question 1

when to use titration method

Answer 1

acid and alkali to make pure sample of crystals or work out concentration of acid/alkali

Question 2

titration method

Answer 2

• use a pipette to measure out 25cm cubed of alkali and place it in a conical flask
• add a binary indicator, eg phenolphthalein
• put the acid in the burette and let it drop to get a rough titre, until the solution changes colour, making sure to shake it gently.
• repeat this until you achieve 3 concordant results with dripwise
• repeat this experiment again to the exact titre without the indicator
• take this solution, put it in an evaporating basin and heat it until saturated
• leave it to cool and crystallise overnight
• filter the crystals
• pat it fry with filter paper

Question 3

when to use excess base method

Answer 3

solid base and an acid

Question 4

excess base method

Answer 4

• gently heat the acid over a bunsen burner
• add the excess solid base overt the heat and stir
• filter the solution to remove excess base
• put it in an evaporating basin and heat until saturated
• leave it to cool and crystallise overnight
• filter the crystals
• pat dry with filter paper

Question 5

when to use precipitate method

Answer 5

when the solid you are making is insoluble

Question 6

precipitate method

Answer 6

• mix the base and acid together
• let the precipitate form
• filter the solution to separate the precipitate and solution
• wash the precipitate with water to remove remaining solution
• let the precipitate dry