Reactivity 3.1 Flashcards
Arrhenius theory
Acids are substances that dissociate in aqueous solution to produce H+ ions (protons)
What happens when protons combined with water?
Hydronium ions are formed (H3O+)
How can an acid be neutralised?
By a base to form salt or water
Alkali
Soluble bases which form OH- in solution
Bronsted Lowry theory
An acid is a substance that can donate a proton and a base is a substance that can accept a proton
Amphoteric
Can act as an acid or base
When Bronsted Lowry acid loses a proton,
It forms a conjugate base
Conjugate acid-base pair
Differs by a single proton H+
pH scale
Measure of the hydrogen ion concentration in aqueous solution
pH when volume or dilution
pH value is independent of volume of solution. Changes when diluted.
pH logarithmic scale
A change of one unit of pH represents a tenfold change in the hydrogen ion concentration
Kw
Ionic product constant for water
Monoprotic acids
Contain one acidic hydrogen atom
Diprotic acids
Contains two acidic hydrogen atom
Two ways to determine pH value of solution
Universal indicator and a pH meter.
Strong acids in aqueous solution
Completely dissociate into their ions
Weak acids in aqueous solution
Partially dissociate into their ions, the weaker the acid/base, the less degree of dissociation
Ka
Acid dissociation constant. The smaller the value of k, the weaker the acid.
Electrical conductivity (strong vs weak acids)
The stronger the acid/base, the high the electrical conductivity.
pH (strong vs weak acids)
The stronger the acid, the lower the pH (compared to the pH of a weak acid of the same concentration)
Chemical reactivity (weak and storng acids)
Acids react with metals to produce H2 gas and undergo neutralisation with metals. Weaker acids have lower reaction rates.
Strong acids - conjugate base
Weak conjugate bases as acid has fully dissociated. Little tendency to gain a proton
Weak acids - conjugate bases
Easily accepts protons from water
Acids neutralisation
Reacting with a base to form salt and water. Exothermic.
Why are neutralisation reactions exothermic?
The only reaction that takes place is the reaction between hydrogen and hydroxide ions to form water and this is exothermic.
Equivalence point
When there are equal amounts of acid and base present in the flask
How can you predict equivalence point?
Where there is a sharp jump on the graph
Methyl orange indicator
Red in acid to yellow in alkali
Bromothymol blue
Yellow in acid to blue in alkali
Phenolphthalin
Colourless in acid to pink in alkali
