Acids, bases & salts Flashcards
Acid
liberate H+ ions in aqueous state
Strong acid
ionises & dissociates completely to liberate all its H+ ions in aqueous state
Examples of strong acids
- H2SO4
- HCL
- HNO3
Weak acid
ionises partially / slightly to liberate a small amount of its H+ ions in aqueous state
Examples of weak acid
- citric acid
- organic acids
Concentrated acids
contains large amount of acid but small amount of water
Dilute acids
contains small amount of acid but large amount of water
Properties of acids
- sour taste
- turn blue litmus paper red
- react with metals to liberate H2 gas with effervescence
- react with carbonates & bicarbonates to liberate CO2 gas with effervescence
- neutralise bases ( metallic oxides & hydroxides )
Bases
oxide / hydroxide of a metal that reacts with an acid to form a salt and water only
Soluble metallic hydroxides ; strong alkalis
- KOH
- NaOH
- Ba(OH)2
Slightly soluble metallic hydroxides ; weak alkalis
- Ca(OH)2
- Mg(OH)2
Insoluble metallic hydroxides
- Fe(OH)2
- Cu(OH)2
- AgOH
Alkalis
- soluble metallic hydroxide
- either strong / weak
Strong alkali
ionises completely to liberate all its OH- ions
Weak alkali
ionises partially to liberate a small amount of its OH- ions
Properties of alkalis
- bitter taste
- turn red litmus paper blue
- neutralise acids
- soapy feel to touch ; react with skin
- strong alkalis -> caustic alkalis ; corrode certain materials
- can liberate ammonia gas when heated with any ammonium salt
Neutralisation reaction
reaction between acid & base to form a salt & water only
Salts
chemical containing a cation & anion which is derived from an acid
- also defined as chemical in which the hydrogen ion of an acid has been replaced by a metallic ion or ammonium ion
Normal salt
all the hydrogen of an acid has been replaced by a metal
Acid salt
not all the hydrogen of an acid is replaced by a metal
- formed from dibasic & tribasic acids
Preparation of salts
Soluble salts -> crystallisation
Insoluble salts -> precipitation / double decomposition
Soluble & insoluble salts in water
- all nitrates are soluble
- all salts of K, Na & NH4 are soluble
- all sufates are soluble except those of Ba, Ca, Pb
- all halides ( chlorides, bromides , iodides ) are soluble except those of Pb & Ag
- all carbonates are insoluble except those of K, Na & NH4
Preparation of K, Na & NH4 salts
by titration method using a suitable salt& alkali
( neutralisation reaction )
Preparation of other soluble salts
prepared by adding excess of one of these substances to the appropriate dilute acid :
- Metal
- Metallic oxide
- Metallic hydroxide
- Metallic carbonate
Preparation of insoluble salts
choose 2 soluble reagents ( one can be an acid )
- insoluble salt formed by precipitation reaction
Types of oxides
- basic oxides
- acidic oxides
- amphoteric oxides
- neutral oxides
Basic oxides
oxides of metals
- those soluble in water dissolve to form alkalis
Acidic oxides
oxides of non-metals
- all dissolve in water to form acids
- all react with alkalis to form a salt & water only
Amphoteric oxides
metallic oxides having both basic & acidic properties
- react with acids to form salts & water
- react with alkalis to form salts & water
Neutral oxides
non-metallic oxides having neither basic nor acidic properties ; they react neither with acids nor alkalis
Water of crystallisation
salts combining with water molecules to form hydrated crystals
Anhydrous salts
do not contain water of crystallisation ; often powdery
