Investigating pH Changes Flashcards
How to calibrate a pH meter
Rinse prove in deionised water and dry with paper towel
Place in pH 4 buffer solution
Wait for reading to remain steady thenset pH meter to pH 4
Rinse again and place in buffer of pH 10
Wait for reading to steady and set meter to 10
How to plot pH curve
Measure pH before solution added from burette
Add solution from burette 1cm3 at a time
Stir
Record pH after each addition
Add solution in burette by 0.1cm3 near endpoint
After end point add solution 1cm3 until in XS
What is the equivalence point
When sufficient base has been added to neutralise acid
How to calculate Ka from pH curve
At half equivalence, pH = pKa
Read off value at equivalence Divide this volume in two Read pH at half equivalence This is pKa Ka= 10^-pKa
Properties of a suitable indicator
Sharp colour change rather than gradual
End point of titration given by indicator must be the same as equivalence point
Indicator should give a distinct colour change
What is the pH range of
a) phenolphthalein
b) methyl orange
8-10
3-5
Colour of phenolphthalein in
a) acid
b) alkali
a) colourless
b) pink
Colour of methyl orange in
a) acid
b) alkali
a) red
b) yellow
What is the pKa of phenolphthalein
9.3
What is the pKa of methyl orange
3.7
