Bases are oxides and hydroxides of metals. They neutralize acids .
Examples : CuO (copper oxide) and NaOH (sodium hydroxide)
Alkalis are soluble bases. They can dissolve in water to release hydroxide ions .Salts are ionic compounds formed when the hydrogen ions, H+ in an acid are completely or partially replaced by a metal ion or an ammonium ion, NH4+.
Indicatior Color in Acid Color in Alkali Color in Neutral
Litmus Red Blue Purple Thymolphthalein Colorless Blue Colorless Methyl orange Red Yellow Orange
base + acid -> salt + water base (alkali) + ammonium salt -> salt + water + ammonia gas
Aqueous solutions of acids contain hydrogen (H+) ions .
Aqueous solutions of alkalis contain hydroxide (OH-) ions .
Universal indicator changes color gradually depending on the concentration of H+ ions in a solution :
pH 0 to 6 (acidic) : A high H+ conc. corresponds to lower pH numbers . For universal indicators, acidic solutions turn deep red/orange , meanwhile weak acids turn yellow/light green .pH 7 (neutral) : Equal conc. of H+ and OH- ions. Universal indicator turns green .pH 8 to 14 (alkaline) : Higher OH- conc. corresponds to higher pH numbers . Turns blue/deep purple.
The equation for the neutralization reaction between an acid and an alkali to produce water :
H+ (aq) + OH- (aq) -> H2O (l)
Acids are proton donors .Bases are proton acceptors .
Strong/weak and concentrated/dilute describe completely different properties.
Strength refers strictly to the percentage of acid molecules that split into ions when dissolved into water .
A strong acid is an acid that is completely dissociated in aqueous solution.
Every single acid molecule breaks apart to release H+ ions. An example is hydrochloric acid . HCl (aq) -> H+ (aq) + Cl- (aq)
A weak acid is an acid that is partially dissociated in aqueous solution.
Only a tiny fraction of the molecules split into ions. The rest remain intact as whole molecules .An example is ethanoic acid . CH3COOH (aq) ⇌ H+ (aq) + CH3COO- (aq)