TOPIC 3- chemical changes
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Acid
Substance w a pH of less than 7. Forms H+ ions in water. Higher concentration of H+ ions, more acidic
Base
A substance that reacts with an acid to produce a salt and water.
Alkali
Soluble base that forms hydroxide ions (OH-) in water. Higher concentration of OH-, higher pH.
Base + Acid»_space;
Salt + H2O
Indicator
Dye that changes colour depending on whether it’s above/below a certain pH.
How is litmus paper affected by pH?
Turns red in acidic solutions, purple in neutral, blue in alkali
How’s is Methyll orange affected by pH?
Red in acidic conditions, yellow in neutral/alkaline conditions.
How’s phenolphthalein affected by pH?
Colourless in acidic/neutral solutions and pink in alkaline conditions.
Neutralisation
Reaction between an acid and a base, producing salt and water.
What are the ions in a neutral solutions?
Hydrogen ions are equal to hydroxide ions.
Dissociation of strong acids in water.
Ionise almost completely w low pH’s (0-2).
Dissociation of weak acids in water
Don’t fully ionise in solution, pH of 4-6.
Acid strength
What proportion of acid molecules ionise in water.
Concentration
How much acid is in one litre (dm cubed)
How does changing concentration affect pH?
Concentration of H+ ions increase by factor of 10 and pH decreases by 1. Opposite effect for decrease in volume. (Eg decrease of 10p = decrease of 2 pH)
Neutralisation reaction
Reaction between an acid and a base
Hydrogen ion
H+
Ammonium ion
NH4+
Hydroxide ion
OH-
Nitrate ion
NO3-
Oxide ion
O2-
Sulfide ion
S2-
Sulfate ion
SO42-
Carbonate ion
CO32-