Ch4_Pract2
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Transcript of Ch4_Pract2
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Cambridge International AS and A Level Chemistry Original material © Cambridge University Press 2011 1
Practical 4.2
Intermolecular bonding
Safety
Wear eye protection at all times. There must be no naked flames in the room.
Hexane, cyclohexane, ethanol, propanone and propanol1ol are flammable and are harmful if inhaled. Ethanol and propanone are also harmful if swallowed.
Testing the polarity of different liquids
Apparatus (per student)
This practical is arranged as a series of five ‘stations’. Each ‘station’ is equipped with the apparatus listed below and one of the five liquids to be tested.
• one of the following liquids: hexane, cyclohexane, ethanol, distilled water, propanone
• burette labelled with the name of the liquid it contains
• burette stand • 250 cm 3 beaker in a small glass or plastic trough
• polythene rod and a piece of fur or other suitable cloth
• 30 cm ruler • small glass funnel • access to fume cupboard • eye protection
Procedure
1 Make sure that the 250 cm 3 beaker and trough are placed directly under the burette.
2 Place the ruler under the trough in such a way that you can measure any deflection of the stream of liquid if it occurs.
3 Vigorously rub the polythene rod with the cloth.
4 Open the burette tap and hold the rod close to the stream of liquid.
5 Measure the deflection (in centimetres) of the liquid stream, if any. Record your result in a suitable table.
6 When you have measured the deflection, replace the liquid in the burette and move on to the next liquid.
Questions
1 Draw the displayed formulae of the compounds you have tested and mark on them any permanent dipoles present. [10]
2 What is the connection between any dipoles present and the deflection of the liquid stream? Explain this observation. Illustrate your answer with a diagram showing the deflection of the liquid stream, the charges on the rod and the alignment of dipoles on molecules in the liquid. [4]
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Practical 4.2
Cambridge International AS and A Level Chemistry Original material © Cambridge University Press 2011 2
The effect of hydrogen bonding on the flow of liquids
Apparatus (per group of students)
• three burettes with suitable stoppers • three burette stands • three small funnels • stopwatch • 100 cm 3 of each of the following liquids: propan1ol, propan1,2diol,
propan1,2,3triol (glycerol)
Procedure
1 Fill the first burette to the 50 cm 3 mark with propan1ol. This will leave some space at the top of the burette that will act as a ‘bubble’.
2 Stopper the burette and then invert it, whilst at the same time starting the stopwatch.
3 When the ‘bubble’ gets to the top of the inverted burette, stop the stopwatch and record the time taken.
4 Repeat steps 1–3 with propan1,2diol and with propan1,2,3triol (glycerol).
5 Tabulate your results, recording the displayed formula and the time taken (in seconds) for the bubble to travel up the tube.
Questions
1 Draw the displayed formulae of the three molecules, showing the dipoles present. [6]
2 Draw a diagram to show the hydrogen bonding present between molecules of propan1ol. [4]
3 Explain your results using the concept of hydrogen bonding. [5]
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Practical 4.2
Cambridge International AS and A Level Chemistry Original material © Cambridge University Press 2011 3
The anomalous properties of water
Apparatus (per group of students)
• ice • 250 cm 3 beaker
• small needle or pin • piece of tissue paper
Procedure
1 Place some ice in a beaker of water. Describe what you see.
2 Your teacher will prepare some hydrogen sulfide (TOXIC, FLAMMABLE) in the fume cupboard. Describe this compound.
3 Fill a beaker almost to the rim with water. Place the needle on the tissue and lay them on the surface of the water. Allow the tissue to absorb water and sink to the bottom of the beaker. Draw a diagram of the pin on the surface of the water, seen from the side.
Questions
1 Explain your observations of the ice in the water. Use a diagram to illustrate your answer. [5]
2 Explain the differences in physical properties between the water and the hydrogen sulfide. [5]
3 Explain the observation with the pin and the water. [2]