Unit 2 ) 4) Strong And Weak Acids And Bases 2 - Calculations And Also Their Salts Flashcards
Compare conductivity , ph , rate of reaction and volume to neutralise acids of strong and weak acids
———————————- Strong acid ————————————————— weak acid
Conductivity ————— higher ———————————————————— lower
Rate of reaction ——— Faster ———————————————————— slower
pH ————————— lower ————————————————————- higher
Volume to neutralise acid : same ——————————————————— same
Y
Y
Explain the differences in pH , conductivity and rate of reaction in strong and weak acids
- difference in conductivity , pH and rate of reaction can be attributed to the fact that strong acids have a much higher number of hydrogen ions in solution than weak acids ( of the same concentration )
Explain why the volume to neutralise an acid is the same for a strong acid and a weak acid of the same concentration
- hydroxide ions in the alkali react with all the available hydrogen ions in solution in a strong acid
- in a weak acid this happens , but it removes hydrogen ions from the equilibrium and causes the acid molecules to release more hydrogen ions - this continues until all the acid molecules have disassociated(ie until the acid is neutralised ) the volume of alkali required therefore only depends on the concentration of the acid - not the strength
Example :
If you were to carry out a titration neutralising say 25cm3 of 0.10 mol NaOH you would find that 25cm3 of either 0.10 mol HCL (strong acid )would be required or 0.10 mol CH3COOH would be required. We say that strong and weak acids do not differ in the stoichiometry of their reactions. Same is true for strong and weak bases
Compare conductivity , pH and volume to neutralise alkali od strong and weak bases
———————————- Strong base ————————————————— weak base
Conductivity ————— higher ———————————————————— lower
pH ————————— higher ————————————————————- lower
Volume to neutralise acid : same ——————————————————— same
With bases : The greater the (OH) conc the higher the ____ and the greater the ______
With bases : The greater the hydroxide concentration the higher the pH and the greater the conductivity
Formula used to calculate pH of weak acid
pH = 1/2pKa- 1/2logc
Explanation - weak acid formula for working pH
-
What is a salt and how does it form
- salts are most simply defined as one of the products of the neutralisation of an acid by a base
- a salt is formed when the hydrogen ions of an acid are replaced by metal ions or ammonium ions
How are salts named
- first part
- end part
- The first part of the name of a salt identifies which alkali / base was used to make the salt
- salts are generally made using sodium hydroxide and potassium salts made using potassium hydroxide as the alkali
- The second part of the name of a salt identifies the acid used to make the salt. Chloride salts are made from hydrochloric acid. Nitrate salts from nitric acid and sulfate salts from sulfuric acids
Some salt solutions are ______ but not all
Some salt solutions are neutral but not all
What does the pH of a salt solution depend on
The pH of a salt solution depends on the reactive strength of the parent acid and parent base
- you can imagine the acid trying to pull the pH towards the acidic side but being opposed by the base pulling in the opposite direction as in a tug of war. Whichever is stronger pulls the pH towards its end of the scale.
Soluble salt of strong acid and strong base
- give example
- what does the solution of salt consist of
- what is the pH
- explain the pH
- a sodium chloride solution contains a mixture of following ions : Na and Cl from the salt , H and OH from the partial ionisation if water. Parent acid (HCL) and parent base (NaOH ) are fully ionised in water
- pH is 7
This is because in solution the sodium ions have no tendency to associate with the hydroxide ions from the water (sodium hydroxide is strong base) and the chloride from the salt has no tendency to associate with the hydrogen from the water (hydrochloric acid is a strong acid ) - parent acid and parent base dissocate fully,
- the water equilibrium is not disturbed by either of the ions from the salt
Soluble Salt of weak acid and strong base
- give example
- what does salt solution consist of
- what is pH
- explain the pH
- sodium ethanoate solution (sodium hydroxide and ethanoic acid ) consist of the following ions - Na+ and CH3COO- from the salt , and H+ and OH- from the partial ionisation of water
The ph is going to be more than 7
- the ethanoate ions (conjugate base of the acid) reacts with H ions from the water , forming more acid
- this results in the water equilibrium creating excess/more of OH ions
So therefore the water dissociation equilibrium is disturbed by the ethanoate ions from the salt
Soluble salt of strong acid and weak base
- give example
- what does salt solution consist of
- what is pH
- explain the pH
- a solution of ethyl ammonium chloride contains a mixture of the following ions : ethyl ammonium ions (C2H5NH3+) ,Cl- ions from the salt and H+ and OH- ions from the partial ionisation from water
pH is less than 7
- This is because in solution ethyl ammonium ions (conjugate acid) from the salt associate with hydroxide ions from the water
- this results in water equilibrium creating more H30 (hydrogen) ions
The water dissociation equilibrium is disturbed by the ethylammonium ions from the salt
