Lesson 7: Titrations

Question 1

What is the starting- colour of methyl orange if we start with an alkali?

Answer 1

• Alkali
• Methyl orange = yellow.
• (changes to red when it is in acidic conditions .)

Question 2

What is the starting colour of methyl- orange if we start with an acid?

Answer 2

• Acid
• Methyl orange = red
• Changes to yellow when in alkaline conditions.

Question 3

What is the method of carrying out the titration for sodium hydroxide?

Answer 3

1.) Use a pipette to transfer 25cm³ of sodium hydroxide to conical flask.
2.) Add 5 drops of methyl orange
3.) Place conical flask on white tile (to see colour change more clearly.)
4.) Fill the burette with sulphuric acid to the 0 - mark, using a funnel (known concentration.)
5.) Add acid to alkali until solution is neutral.
6.) Keep swirling to ensure the acid has spread.
7.) When it gets close, start acid down drop- by- drop.
8.) Methyl orange will turn a permanent red when it is neutral.

Question 4

What is a safety- precaution when pouring the acid into the burette?

Answer 4

• Do it below eye- level.
• Don’t want to be looking up if acid spills.
• Wear goggles as well….

Question 5

What do you do after you have finished the 1st titration?

Answer 5

• repeat it several times
• Until you get values within 0.1 of each other.
• Then, calculate a mean of the results.

Question 6

Why don’t we use universal indicator in titrations?

Answer 6

• We don’t want to see a gradual change in colour.
• We need a sudden colour change - showing the** end point **

Question 7

Q.)

Explain why burette is used for sulphuric acid but pipette is used for sodium hydroxide.

Answer 7

• Pipette is used to measure fixed volume.
• Burette is used to measure variable volume.