pH And Indicators (T4)

Question 1

What does the PH of a substance refer to?

Answer 1

The activity of the hydrogen ions contained within a chemical, which can cause the chemical to react in certain ways with other substances

Question 2

What does pH 7 mean?

Answer 2

• the substance is neutral

- it does not posses the same corrosive qualities of either acids or bases

Question 3

If a substance has a pH of 2 or less we say it is…

Answer 3

Strongly acidic

Question 4

What do we use to estimate pH? Give some examples..

Answer 4

• we use chemicals called indicators
• the chemicals change colour depending on the pH

Eg: methyl orange, phenolphthalein, litmus etc.

Question 5

What is an ‘indicator’?

Answer 5

A substance that changes colour when added to acidic or alkaline solutions

For example, litmus or universal indicator

Question 6

Litmus indicator is one of the most commonly used indicator solutions used in the laboratory. What colour does it turn in acidic, alkaline and neutral conditions?

Answer 6

• acidic: red
• alkaline: blue
• neutral: purple

Question 7

What is a more reliable alternative to litmus indicator solution and what colour does it turn in acidic, alkaline and neutral conditions?

Answer 7

• litmus paper
• it comes as red litmus paper and blue litmus paper

- red litmus paper:
Acidic solution (stays red)
Neutral solution (stays red)
Alkaline solution (turns blue)

- blue litmus paper:
Acidic solution (turns red)
Neutral solution (stays blue)
Alkaline solution (stays blue)

Question 8

What is universal indicator and what makes it more accurate?

Answer 8

• it is a mixture of several different indicators
• it can show us exactly how acidic or alkaline a solution is as it has many different colour changes, for each stage of the pH scale (0-14)
• red is for strong acids, green for neutral and dark purple for strong bases

Question 9

What range is the pH scale?

Answer 9

pH 0 - pH 14