Acids and bases: pH curves and indicators

Question 1

What colour is phenolphthalein in acidic/neutral solution

Answer 1

colourless

Question 2

What colour is phenolphthalein in alkaline solution

Answer 2

Pink

Question 3

What is the range in which phenolphthalein changes colour

Answer 3

8.20-10.00

Question 4

What colour is methyl orange in acidic solution

Answer 4

red

Question 5

What colour is methyl orange in neutral/alkaline solution

Answer 5

yellow

Question 6

In what pH range does methyl orange change colour in

Answer 6

3.20-4.40

Question 7

Define the equivalence point

Answer 7

Where moles of alkali added are equal to moles of acid present

Question 8

What does the equivalence point look like on a pH curve

Answer 8

Rapid change in pH

Question 9

What is observed at the end point of a titration

Answer 9

Indicator change in colour

Question 10

How do you select an indicator to use based on the pH curve

Answer 10

Indicator must change colour entirely within the vertical part of the graph

Question 11

Define a buffer

Answer 11

solution that resists changes in pH when small amounts of acid or alkali are added

Question 12

What are acidic buffers made of

Answer 12

A weak acid and one of its salts (HA and A-)

Question 13

What are basic buffers made of

Answer 13

Weak alkali and one of its salts

Question 14

How do both buffers work

Answer 14

In acidic buffers HA and A- conc are much higher than that of H+

In basic buffers conc of base and salt are much higher than that of OH-

Question 15

Which Ka equation is used when calucating pH of buffers

Answer 15

KA=
[H+][A-]
——————-
[HA]