PAG 11: pH measurement Flashcards
Give 3 ways you could identify whether a solution was acidic or basic
- Litmus paper
- Indicator (e.g. universal indicator) and comparison to a colour scale
- pH meter
How can litmus paper be used to identify an alkali?
Red litmus paper will turn blue
Blue litmus paper will remain blue
How can litmus paper be used to identify an acid?
Blue litmus paper will turn red
Red litmus paper will remain red
Why might a pH meter be used rather than universal indicator to measure pH?
- Gives a numerical value for pH
- More accurate (typically read to 2 decimal places)
What is meant by term ‘accuracy’?
How close the measurement is to the true value
What equations link to pH and hydrogen ion concentration?
pH= -log[H^+]
[H^+]= 10^-pH
Briefly outline how to carry out a titration
- Use a pipette to measure the first solution into a conical flask
- Add a few drops of a suitable indicator
- Add the other solution into a burette and record initial volume
- Slowly add solution in the burette into the conical flask
- Swirl the mixture continuously until the end point is reached
- Repeat until concordant results are obtained
What colour is methyl orange in:
a) acid?
b) alkali?
c) neutral solution?
a) red
b) yellow
c) orange
What is colour of phenolphthalein in:
a) acid?
b) alkali?
a) colourless
b) pink
What is a Bronsted-Lowry acid?
A substance that donates protons (H^+)
What is a Bronsted-Lowry base?
A substance that accepts protons (H^+)
What is the difference between a strong and weak acid?
A strong acid completely dissociates in solution (readily releases H^+ ions) whereas a weak acid only partially dissociates
A solution has a pH of 1.00 when measured using a pH meter. Suggest characteristics of this solution?
- Acidic
- Likely to contain a strong acid
