acids, bases and salts 🧂 Flashcards
what is an acid?
a substance which dissociates in water / aqueous solution to give hydrogen ions
define basicity of acids
the number of hydrogen ions produced by one molecule of acid when the acid molecule dissociates in water
define strength of acids
the extent of dissociation of acid molecules in water (completely vs partially)
what is a base?
base is a substance that reacts with acid to form salt and water only
what does pH measure?
measures acidity of alkalinity by measuring concentration of hydrogen ions in a solution
3 main indicators + colour changes
1) litmus: red to blue at pH 7
2) phenolphthalein: colourless to pink at pH 9
3) methyl orange: red to yellow at pH 4
suitable indicator for titration explanation
the pH at which the indicator changes colour, pH _, falls within the sharp decrease of the titration curve / equivalence point, pH _ to pH _
what are basic oxides?
oxides of metals, if soluble they dissolve in water to form alkalis
what are acidic oxides?
covalent compounds, usually dissolving in water to produce acids
what are amphoteric oxides?
ZnO, PbO and Al2O3, can behave as acidic or basic oxides
what are neutral oxides?
covalent compounds
methods of preparation of salts and their criteria
1) precipitation: two aqueous reactants, solid product
2) reaction of acid with excess insoluble base, carbonate or metal: soluble product
3) titration: very reactive metals / excess soluble base that cannot be filtered out
why is insoluble reactant unsuitable for producing insoluble salt?
insoluble salt will coat onto insoluble reactant, preventing further reaction between the reactant and the acid
procedure for precipitation
1) mix the aqueous solutions in a beaker
2) stir well. a white precipitate will be formed
3) filter the mixture to obtain salt as the residue
4) wash the residue with deionised water and dry between two pieces of filter paper
procedure for reaction w excess insoluble reactant
1) heat the acid in the beaker
2) add excess insoluble reactant to the acid
3) stir the mixture well
4) filter the mixture to obtain excess insoluble reactant as the residue and aqueous product as the filtrate
5) heat the filtrate to obtain a hot, saturated solution
6) cool the hot, saturated solution to obtain crystals
7) filter the mixture to collect crystals as the residue
8) dry the crystals between two pieces of filter paper
