salts 5.3
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how do you make soluble salts by neutralising acids?
acid (aq) + base (s)/alkali (aq) > salt (aq) + water (l)
the two stages of making pure, dry crystals of a soluble salt:
• make a salt solution this can be done with two different methods, depending on what type of salt your making a. insoluble base method b. titration method • then you crystallise the salt
what is the insoluble base method?
do this when making salts that do not contain Na=, K= or NH4+ ions • choose the acid and base (usually solid metal oxide) • heat the acid (more energy so reacts faster) • stir and add base until no more can be dissolved (base will be in excess therefore we know acid has been all used up) • filter out excess base • the acid and base form salt and water
what is the titration method?
do this when making salts that contain Na+, K+ or NH4+ ions as they are soluble • choose acid (usually HCl, H2SO4, HNO3) and alkali (usually NaOH, KOH, NH4OH) • perform titration to measure the volume of acid and alkali that neutralise each other • repeat titration but don’t put the indicator in and use the burette to add exactly the right volume for neutralisation • acid and alkali form salt and water
stages of making pure, dry crystals of a soluble salt: what do you do once you have make your salt?
crystallisation • heat salt solution until crystals start forming causing solution to become saturated • allow solution to cool in the evaporation basin, lowering the solubility of the salt so that lots of crystals form • filter out the crystals, removing them from the excess salt solution in the basin • dry the crystals by dabbing them with filter paper, removing the last traces of water from the crystals
how can we make insoluble salts?
by mixing solution to make a precipitate
process of making insoluble salts by precipitation:
for example to make BaSO4 precipitate we could mix: BaCl2 and Na2SO4 they would collide and the ions would combine but the Na and Cl aren’t involved, we would call them spectator ions then need to separate the salt from the solution: - filter out the salt precipitate (the residue is the salt we want keep, filtrate is the leftover solution) - rise the salt with water (washes off traces of leftover solution) - dry the salt by dabbing with water