EL - Equilibria (acid–base) *02

Question 1

basic nature of oxides and hydroxides

Answer 1

they form alkaline solutions in water

1. oxides of group 2 metals react readily with water —> form metal hydroxides, which dissolve - the OH- makes these solutions strongly alkaline

CaO (s) + H2O (l) —–> Ca 2+ (aq) + 2OH- (aq)

MgO only exception - reacts slowly and hydroxide not very soluble

Question 2

do group 2 oxides and hydroxides neutralise acids?

Answer 2

yes

can neutralise dilute acids forming solutions of the corresponding salts (and water)

Question 3

making soluble salts - using a metal or an insoluble base

Answer 3

need the right acid and a suitable metal or an insoluble base (metal oxide or hydroxide)
eg, chlorides = HCl, sulfates = H2SO4, nitrates = HNO3
add solid metal to acid, it will dissolve —> will know its neutralised as no more acid will dissolve

filter out excess metal (that hasnt dissolved)

to get pure solid crystals of salt - evaporate off the water, then leave the rest to evaporate slowly
—> CRYSTALLISATION

Question 4

making soluble salts - using an alkali

Answer 4

titration

• need to add exactly the right amount of alkali (cant just add excess and filter - both aq)
• need to use an indicator

then evaporate off the water and leave to crystallize

Question 5

making insoluble salts

Answer 5

precipitation reaction

occur in aqueous solutions when cation and anions combine to form an insoluble ionic salt

react what you need —> salt will precipitate

filter solution, wash and dry