Electricity and Magnetism

Knowledge Area: Electricity and Magnetism

Topic: Internal resistance and Series-Parallel networks

Part 1


To determine the internal resistance of a battery


Do not leave the switch closed at all times.  The battery will run flat. Close the switch only for taking the readings on the voltmeter and Ammeter.  Take your readings accurately. Do not conduct the experiment with wet hands.


Place 4 x 1,5V cells in a cell holder in a series connection.  Connect a Switch, Ammeter and a Rheostat in series to the battery.  Connect the Voltmeter across the battery.

If a rheostat is not available, resistors or bulbs could be used in the place of a rheostat. The resistors or bulbs must be connected in series.  One resistor/bulb must be connected first and then the resistors/bulbs be increased to two in series, three in series, etc.

Draw the electrical circuit diagram. Set the Rheostat at 10W. Close the switch and reduce the resistance in the Rheostat step by step, increasing the current at the same time. Take the ammeter and voltmeter readings in each case/step. Open the switch while recording the readings in order to spare the batteries’ life span.

Take and record a minimum of 5 readings. Interpret and analyse the data in order to determine the internal resistance. Write a conclusion and prepare a report (write-up).

Part 2


  1. To determine the equivalent resistance in a Series-parallel network electrical circuit.
  2. To compare the experimental values of the equivalent resistance to the theoretical values.


Place 4 x 1.5V cells in a cell in a cell holder in a series connection. Connect a voltmeter (V1) across the battery. Connect three resistors of different resistance. One resistor must be connected in series with a voltmeter (V2) across and the other two resistors must be connected in parallel with a voltmeter across (V3). Connect a switch and an ammeter.

Preparation and identification of Esters

  1. Title

Preparation and identification of Esters 

  1. Aim of the experiment

* To synthesize/prepare esters, methylbutanoate and ethylbutanoate.

* To write the chemical equations for the formation of methylbutanoate and

ethylbutanoate using structural formulas.


  1. Materials/Apparatus

Equipment/ Glasswares                       Chemical / Reagents

2 test tubes                                           Methanol

Water soluble marker                          Ethanol

Test tube rack                                      Concentrated sulphuric acid

Eye dropper                                         Butanoic acid

2 x 250 ml beakers

Hot plate

10 ml graduated cylinder


Lab apron & Safety goggles

Water bath


  1. Safety Precautions


  • Concentrated sulphuric acid is a strong oxidizing agent and highly corrosive. It is dangerous and can burn skin, eyes, and clothing very badly. Avoid contact with skin or clothes. Wear gloves and proper eye protection when using this substance. Use only in a fume hood. Use exactly as directed. If it is spilled, wash immediately before the acid has a chance to cause a burn, and inform the instructor.
  • Butanoic acid (all organic liquid acids) is toxic and corrosive to skin, eyes, and clothing. While working on this experiment, wear safety goggles, full face shield, gloves, and lab apron. Wash spills and splashes off your skin and clothing immediately, using plenty of water.
  • All burners and other flames in the laboratory must be extinguished before you start this experiment.
  • Methanol is highly flammable. It is poisonous if swallowed. Its vapour is harmful to the eyes, lungs and skin and other organs.
  • Ethanol is flammable, poisonous and its toxic.
  • Detect odours of these esters with caution because vapors produced may be harmful. Breathing the vapours of some of these esters can cause sore throat, dizziness, headache, and drowsiness. Hold the test tube 30 cm away and 15 cm below your nose. Waft a small amount of vapor or odour from the ester toward your nose, sniffing cautiously, once or twice. Do not breathe deeply while sniffing.
  • Before leaving the laboratory, wash your hands thoroughly with soap and water.



  1. Safety audit on:
  • Ethanol
  • Methanol
  • Butanoic acid
  • Sulphuric acid
  1. Procedure/Method
  2. Put on your lab apron and safety goggles.
  3. Label the two test tubes 1 and 2 with your water soluble marker and place them in the test tube rack.
  4. Into test tube 1, pour 5cm3 of methanol and in test tube 2, 5cm3 of ethanol and then add 6cm3 of butanoic acid as indicated in Table 1 below. Smell the mixture in each test tube as per safety precaution, above (waft!).


Table 1 –Reagents for preparation of esters

Test tube Constituents
1 5 cm3 methanol +  6 cm3 butanoic acid
2 5 cm3 ethanol + 6 cm3 butanoic acid


  1. Add 4 drops of concentrated sulphuric acid to each test tube.
  2. Pour about 150 ml of tap water in a 250 ml beaker. Place the test tubes in the water and heat the water on a hot plate to a temperature of about 60˚C – 75˚ Leave the test tubes in the hot water bath for 15 minutes.
  3. Cool the test tubes by immersing them in cold water in another beaker.
  4. Add 5 ml of distilled water to each of the test tubes.

Carefully note the odour of the contents of each of the test tubes in your copy of Table 2 in your notebook. Hold the test tube about 30 cm away from your nose and gently waft the vapour towards your nose without inhaling deeply. Each of the odours should be somewhat familiar to you. Alternatively, the contents of the test tube may be poured into a beaker half full of water and the odour above it detected carefully.

  1. Dispose of all materials following the reagent disposal instructions.
  2. Before leaving the laboratory, wash your hands thoroughly with soap and water.


  1. Observations and recording

               Table 2 – Odours of Esters

Test tube Aroma(smell) Constituents
1   Methanol + butanoic acid
2   Ethanol + butanoic acid


  1. Analysis and interpretation
  • Identify the esters formed in relation to the odours smelt.
  • Draw the structural formulae of the formation of the two esters.


  1. Conclusion

Make a list of the odours you were able to detect and the ester responsible for

that odour.


  1. Factors influencing results

Mention all limitations and challenges in this experiment.

  1. Conceptual questions (Questions related to the experiment)



  1. Write down the general equation for the reaction of an alcohol and a carboxylic acid                                                 (3)
  2. Name the ester formed in each of the test tubes (Table 2, above).         (4)
  3. What is the function of sulphuric acid in these reactions?                                     (2)
  4. How would you dilute a concentrated sulphuric acid solution? (2)
  5. Write 5 safety precautions that you took during this experiment             (5)
  6. Give four (4) uses of esters (4)




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