19: Neutralisation Flashcards
How does a pH meter work
A pH meter had a probe which dips into the solution. The probe houses an electrochemical cell, where the cell potential depends on the [H†] in the solution.
The pH meter measures the voltage and converts it into a pH reading
The pH meter is calibrated using solutions of accurately known pH before use
What does the titration curve look like for a strong acid and strong base
S shaped curve starting from around 1 pH and finishing at like 13 pH. With vertical region around pH 7
What does a titration curve look like for a weak acid, strong base
Starts at around pH 3 and finishes at about pH 13
The centre of its vertical region is above pH 7
What does the titration curve look like for a strong acid, weak base
Starts at around 1 pH and finishes at about pH 11
Centre of vertical region is below pH 7
What does the titration curve look like for a weak acid / weak base
Starts at around pH 3 and finishes at pH 11
No vertical region
What are indicators made of
Weak acids which have different colours in the dissociated and undissociated form
When is an indicator good for detecting the end point of the titration
Needs to have a sharp colour change in the volume range very close to the true endpoint (the vertical region on the curve)
Describe the temperature change when an alkali is being added to an acid
The temperature initially rises as the exothermic reaction takes place
Once the equivalence point is reached no further reaction takes place so no more heat is released
The temperature then steadily drops as further (cold) alkali is added
How can you use a graph of temp against volume of alkali added to calculate ΔneutH
Take ΔT from the graph (peak T value - initial T)
Sub ΔT into q = mcΔT
to find ΔneutH
