PAG 11 - pH measurement

Question 1

Give 3 ways you could identify whether a

solution was acidic or basic

Answer 1

1. Litmus paper
2. Indicator (e.g. universal indicator) and
   comparison to a colour scale
3. pH meter

Question 2

How can litmus paper be used to identify

an alkali?

Answer 2

Red litmus paper will turn blue

Blue litmus paper will remain blue

Question 3

How can litmus paper be used to identify

an acid?

Answer 3

Blue litmus paper will turn red

Red litmus paper will remain red

Question 4

Why might a pH meter be used rather

than universal indicator to measure pH?

Answer 4

• Gives a numerical value for pH
• More accurate (typically read to 2
  decimal places

Question 5

What is meant by the term ‘accuracy’?

Answer 5

How close the measurement is to the

true value

Question 6

What equations link pH and hydrogen

ion concentration?

Answer 6

pH = -log[H+]
[H+] = 10-pH

Question 7

Briefly outline how to carry out a titration

Answer 7

1. Use a pipette to measure the first solution into a conical
   flask
2. Add a few drops of a suitable indicator
3. Add the other solution into a burette and record the initial
   volume
4. Slowly add the solution in the burette into the conical flask
5. Swirl the mixture continuously until the end point is reached
6. Repeat until concordant results are obtained

Question 8

What colour is methyl orange in:

a) Acid?
b) Alkali?
c) Neutral solution?

Answer 8

a) Red
b) Yellow
c) Orange

Question 9

What is the colour of phenolphthalein in:

a) Acid?
b) Alkali?

Answer 9

a) Colourless

b) Pink

Question 10

What is a Brønsted-Lowry acid?

Answer 10

A substance that donates protons (H+)

Question 11

What is a Brønsted-Lowry base?

Answer 11

A substance that accepts protons (H+)

Question 12

What is the difference between a strong

and weak acid?

Answer 12

A strong acid completely dissociates in
solution (readily releases H+
 ions)
whereas a weak acid only partially
dissociates

Question 13

A solution has a pH of 1.00 when
measured using a pH meter. Suggest the
characteristics of this solution

Answer 13

• Acidic

- Likely to contain a strong acid