3.1.2 AMOUNT OF SUBSTANCE

Question 1

State the conversion between g to mg:

Answer 1

x1000

Question 2

State why it’s important to fill the space below the tap in the burette before beginning an accurate titration (1)

Answer 2

make sure an incorrect volume is not recorded/

Question 3

State why rinsing the inside of the conical flask with distilled water during a titration can improve the accuracy of the end point (1)

Answer 3

Any reagents that are stuck on the side of the flask/left over can be added to the mixture.

Question 4

State why rinsing doesn’t change the volume of solution needed in a titration or the titre value (1)

Answer 4

Water isn’t an acid or alkali so will not change the moles of the solution/reagent.

Question 5

Suggest one reason why a 250cm3 conical flask is preferred to a 250cm3 beaker for a titration:

Answer 5

Reduces the chance of spills when swirling the solution.

Question 6

Suggest why repeating a titration makes the value of average titre more reliable (1)

Answer 6

Titrations can give anomalous results, these can be reduced.

Question 7

Why should small amounts of a substance not be used? (1)

Answer 7

there might be errors in weighing would be too high/percentage errors too high.

Question 8

Why would large amounts of a substance not be used? (1)

Answer 8

There would be an incomplete reaction/decomposition.

Question 9

State a suitable amount of indicator solution that should be added to the flask (1)

Answer 9

2-6 drops/ a few drops.

Question 10

State 4 ways that could improve the overall technique when carrying out a titration

Answer 10

1. Wash the glass rod into the solution to transfer any remaining substance on it.
2. Ensure the bottom of the meniscus is on the graduation mark.
3. invert the volumetric flask 2 times.
4. use a teat pipette to make up the mark on the volumetric flask.

Question 11

What is the hazard and precaution of using an acid?

Answer 11

Can be corrosive and harm the skin and eyes if in contact: wear safety goggles/gloves.

Question 12

What is the hazard and precaution when using a toxic substance?

Answer 12

Toxic vapours can be inhaled; carry out experiment in a fume cupboard.

Question 13

Suggest why the student should use NaOH solution rather than water for the final rinse of the burette.

Answer 13

Water will dilute NaOH and change the concentration.

Question 14

What are concordant titres?

Answer 14

Titres that are within 0.1cm3 within each other.