Chemical Equilibrum 4-6 Flashcards
Why are strong acids/strong bases better at conductivity than weak acids/weak bases.
Because strong acids/bases have a higher hydrogen/hydroxide ion concentration.
What kind of pH does a salt of a strong acid and strong base have?
Neutral - As both parents are fully ionised in water they have no effect on the equilibrum of water. An example is sodium chloride produced from hydrochloric acid and sodium hydroxide.
What kind of pH does a salt of a strong acid and weak base have?
Acidic - An example is ammonium chloride produced from hydrochloric acid and ammonia. The positive NH4+ ions in ammonium chloride react with the OH- ions in water to form ammonia molecules. This means there are more hydrogen ions thn hydroxide ions in the solution, making it acidic.
What kind of pH does a salt of a strong base and weak acid have?
Alkaline - An example is sodium ethanoate produced from sodium hydroxide and ehtanoic acid. The negative CH3COO- ions react with hydrogen ions in the water to form more ethanoic acid molecules. This means there are more hydroxide ions than hydrogen ions in the solution, making it alkaline.
What kind of pH do soaps have?
Alkaline - Soaps are the salts of fatty acids (weak) and strong bases. Therefore soaps will dissolve in water to form alkaline solutions.
What did Bronsted and Lowry define an acid and base as?
- An acid is a proton donor.
- A base is a proton acceptor.
What is a conjugate base and a conjugate acid?
- A conjugate base is an acid that has donated a proton.
- A conjugate acid is a base that has accepted a proton.
How do you know the concentration of hydrogen ions in a strong monoprotic acid?
It will be the same as the concentration of the acid because strong acids fully dissociate in water meaning all acid molecules will have changed into ions.
Why is it harder to calculate the pH of a weak acid?
Because usually only around 1% of weak acid molecules dissociate into ions in water. Therefore, the hydrogen ion concentration will be much lower than the concentration of the acid.
What is Ka?
The dissociation constant of an acid, given by Ka = (H+)(A-)/(HA), where HA is the acid.
How does the expression for Ka become Ka = (H+)^2/c?
Because very little reactant molecules dissociate into ions, HA is just taken as the original concentration of the acid with the symbol c. For every acid molecule that dissociates into ions one (H+) and one (A-) which means (H+)=(A-). This can then be written as (H+)^2. The equation allows Ka to be calculated or it can be rearranged to calculate (H+).
What is the equation for calculating pKa?
pKa = -log10Ka.
What is the equation for calculating the pH of a weak acid?
pH = 1/2pKa - 1/2log10c.
What is a buffer solution?
A buffer solution is one where the pH remains constant when small amount of acid or alkali are added.
What is an acid buffer?
An acid buffer consists of a solution of weak acid and one of its salts. For example, ethanoic acid and sodium ethanoate. Here, the sodium ions are just spectator ions, and the ethanoate ions are the conjugate base of ethanoic acid.
