Chapter 21 Flashcards
What is a buffer solution
Buffer solution system that minimises pH changes on addition of small amounts of acid or base
How do you prepare a buffer solution
You can use a weak acid and salt of its conjugate base
The acid will partially dissociates and the salt will fully dissociate
You can use a weak acid and a strong alkali
The alkali will fully neutralise the acid
Acid was slightly dissociate
How do buffer solutions control pH when acid is added
The hydrogen ion concentration increases
Hydrogen ions react with conjugate base ions to form acid
Equilibrium shifts to the left to remove H+ ions
How do buffer solutions control PH when alkalis added
Oh- ions concentration increases
H+ reacts with oh- to form H2O
HA dissociates to restore H+ an equilibrium shifts to the right
What assumptions are made when calculating the pH of a buffer solution
Ha is equal to a- (the salt fully dissociates)
Ha is only slightly dissociated
How is the pH of blood controlled
Blood pH needs to be kept between 7.35 and 7.45 using the carbonic acid-hydrogen carbonate buffer solution
How does blood maintain its pH when acid is added
Hydrogen ion concentration increases
Hydrogen ions react with hydrogen carbonate ions
Equilibrium shifts to the left removing H+
How does blood maintain pH when alkali is added
Oh - concentration increases
H+ reacts with oh minus to make water
Carbonic acid dissociates shifting equilibrium right to restore H+
Why does the pH titration curve has an s shape
At the start acid is an excess of the pH increases very slightly
In the centre pH increases rapidly and we reach the equivalent point whether volume of one solution exactly reacts the volume of another
At the end of bases in excess so pH increases very slightly
What is an indicator
An acid base indicator is a weak acid that has a distinctively different colour from it’s conjugate base
The equilibrium position is shifted towards the weak acid in acidic conditions and the conjugate base in basic conditions
What happens when you add base to an indicator
The oh minus ions react with the H+ to form water
Acid dissociates
Equilibrium shifts to the right
There is a colour change
What happens when you add acid to an indicator
H+ ions react with a minus ions to form acid
Equilibrium shifts left
There is a colour change
Draw a strong acid strong base titration curve and choose an indicator
Large s shape
Phenolphthalein and methyl orange appropriate
Draw a strong acid weak base titration curve and choose an indicator
A shape with low bottom and low top
methyl orange
Draw a pH titration curve for a weak acid and strong base and choose an indicator
A s shape with high bottom and high top
Phenolphthalein appropriate
