Preparation of salts (6) ✅ Flashcards
(18 cards)
what is a salt
a compound formed when some or all of the hydrogen ions in an acid are replaced by metal ions or ammonium ions
equation for acid reacting with base
acid + base –> salt + water
what is a salts two parts to its name
metal part and acid part
what are the two types of salts
- soluble
- insoluble
what colour does the phenolphthalein indicator turn if a substance is an alkali
pink
what colour does the phenolphthalein indicator turn if a substance is an acid
colourless
what are the two methods used to prepare soluble salts that involve using an acid, preparation and purification
- titration
- acid and excess insoluble solid
what is titration used for and an example
making all sodium and potassium salts
e.g. preparation of sodium chloride
what is the method for titration
( 6 steps)
(NaOH, add phone…, HCL using b until changes from… to …, repeat without, heat, leave to…)
- pipette NaOH into conical flask using pipette filler
- add phenolphthalein
- add hydrochloric acid using burette until indicator changes from PINK - COLOURLESS
- repeat but without adding indicator
- heat to reduce volume by half
- leave retainers to cool and crystallise
- filter and dry
why do crystals form o cooling
because the solubility decreases as temperature decreases
what does the salt look like from the titration experiment
white crystals
why was the indicator needed for the titration experiment
to show when acid + alkali had completely reacted/neutralised each other
why was it repeated without the indicator from the titration experiment
so salt isn’t contaminated with indicator
what would’ve happened if too much salt had been added from the titration experiment
pure salt would not have been formed
how can we remove the indicator after the first titration
adding charcoal, heating and filtering the solution
what is the method for the preparation of copper (II) sulfate
- place sulfuric acid in beaker
- warm, add solid, stir until no more disappears
- filter into evaporating basin
- heat to reduce volume by half
- leave remaining solution to cool and crystallise
- filter crystals and dry
how do we know when a metal carbonate reaction is complete
no more bubbles of gas
no more solid disappears
why do we add solid until no more disappears
to ensure all the acid has reacted and a pure salt is obtained
