Practical Techniques

Question 1

How would you convert between m^3 and dm^3?

Answer 1

1m^ = 1000dm^3

Question 2

How would you convert between dm^3 and cm^3?

Answer 2

1dm^3 = 1000cm^3

Question 3

What must you do if you are looking for a colour change in an experiment?

Answer 3

Put a white back ground behind the reaction container

Question 4

What must you do if you are looking for a precipitate to form?

Answer 4

Mark an X on the piece of paper and place it under the reaction container. Your solution is cloudy when you can no longer see the X

Question 5

When measuring temperature on a thermometer what must you do to make sure your reading is accurate?

Answer 5

1) Wait for the temperature to stabilise before taking an initial reading
2) Read thermometer at eye level

Question 6

What are valid results?

Answer 6

Those that answer the original question. For example you have controlled all your variables.

Question 7

What are accurate results?

Answer 7

They are really close to the true answer.

Question 8

What are precise results?

Answer 8

They can be reproduced in an experiment.

Question 9

How could an experiment be improved?

Answer 9

• Make sure you control all variables
• Was apparatus an appropriate scale for measurements
• Use more accurate equipment
• Repeat experiment

Question 10

How do you set up filtration under reduced pressure?

Answer 10

1) connecting tubing to vacuum outlet and Büchner flask
2) Fit Büchner funnel to Büchner flask with Büchner ring
3) Switch on pump
4) Place filter paper in the funnel and wet with the same solvent

Question 11

How do you perform filtration under reduced pressure?

Answer 11

1) Pour the reaction mixture in
2) Rinse out the beaker with solvent so all crystals collect
3) Rinse crystals in Büchner funnel with more solvent and leave under suction

Question 12

How do you perform recrystallisation?

Answer 12

(1) Warm solvent in a conical flask in a water bath
(2) Dissolve the sample in a minimum amount of hot solvent
(3) Once dissolved allow solution to cool and crystals to form
(5) Filter solid
(6) Wash solid with cold solvent and allow to dry

Question 13

How to investigate melting point?

Answer 13

(1) Place capillary tube into sample hole
(2) Rapid heating and look through window
(3) Once solid is seen to melt record temperature
(4) Do the same but when melting point is approached set to low - accurate

Question 14

Using a Thiele tube to determine melting point

Answer 14

(1) Set up a thiele tube
(2) Attach the capillary tube with sample to a thermometer
(3) Insert the thermometer through a hole in the cork and the capillary tube and thermometer should be touching the oil
(4) Use a micro burner and heat side arm and when it starts to melt record the temp
(5) Heat oil slowly at end

Question 15

How do you separate an organic liquid from its impurities?

Answer 15

1) Heat flask
2) Those with the lowest boiling points will evaporate first and then condense and move down the column into a conical flask
3) When the temperature is close to the value of the boiling point of the desired product switch conical flask and collect liquid until temperature changes

Question 16

Purification of organic liquid

Answer 16

1) Add to separating funnel and shake, the layers should settle
2) Tap off both layers into separate conical flasks
3) Add drying agent e.g CaCl2 to organic layer
4) Filter off drying agent
5) Re-distill