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) Pour chosen solvent into a conical flask and warm over a water bath
(2) Tip the impure sample into a second conical flask
(3) Slowly add solvent to sample (minimum amount)
(4) Once dissolved allow solution to cool and crystals to form
(5) Filter under reduced pressure
(6) Wash solid with cold water and allow to dry

Question 13

How to investigate melting point?

Answer 13

(1) Place capillary tune 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
(4) Use a micro burner and when it starts to melt record the temp

Question 15

How do you purify an organic liquid?

Answer 15

1) Pour the mixture of liquids into a separating funnel, stopper the top and invert to mix
2) Allow the layers to settle
3) Add some water to see which layer increases in volume (the one that does is aqueous)
4) Place the conical flask under separating funnel and remove stopper, letting the first layer drain out
5) Switch the conical flask and do the same for the other layer.

Question 16

How do you dry the organic product?

Answer 16

1) Add the organic liquid top a conical flask
2) Add a spatula of drying agent to the flask and swirl to mix
3) Place a stopper on the flask to prevent the product from evaporating away. Leave.
4) Add more drying agent if the solid has stuck together in a lump as there is still some water present. Do this until some solid has dispersed.
5) Decant the liquid from the solid into a flask and if it is dry it should be clear.