Chipa Maimela GRADE 12 PHYSICAL SCIENCES, PHYSICAL SCIENCES GRADE 12

Alkanes and alkenes react differently with bromine and potassium permanganate.


Reaction of Alkanes with Bromine:

Alkanes typically do not react with bromine in the absence of light or heat. However, when exposed to light or heat, alkanes can undergo a free radical substitution reaction with bromine, which results in the formation of a bromoalkane. The equation for this reaction is:

CnH2n+2 + Br2 → CnH2n+2Br

Reaction of Alkenes with Bromine:

Alkenes can react with bromine in the absence of light or heat. This reaction is called an electrophilic addition reaction, and it results in the formation of a dibromoalkane. The equation for this reaction is:

CnH2n + Br2 → CnH2nBr2

Reaction of Alkanes with Potassium Permanganate:

Alkanes do not react with potassium permanganate in the absence of heat or an acid catalyst. However, when heated with an acid catalyst, alkanes can undergo an oxidation reaction that results in the formation of carboxylic acids or alcohols. The equation for this reaction is:

CnH2n+2 + KMnO4 + H+ → CnH2n+1COOH or CnH2n+1OH

Reaction of Alkenes with Potassium Permanganate:

Alkenes do not react with potassium permanganate in the absence of heat or an acid catalyst. However, when heated with an acid catalyst, alkenes can undergo an oxidation reaction that results in the formation of carboxylic acids or alcohols. The equation for this reaction is:

CnH2n + KMnO4 + H+ → CnH2n-1COOH or CnH2n-1OH

It’s important to note that the reagents used and the conditions for the reaction can affect the products formed in these reactions.

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Chipa Maimela GRADE 12 PHYSICAL SCIENCES, PHYSICAL SCIENCES GRADE 12

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Chipa Maimela EXPERIMENT, GRADE 12 PHYSICAL SCIENCES, GRADE 12 QUESTION PAPERS, PHYSICAL SCIENCES GRADE 12, PRACTICAL INVESTIGATION

GRADE 12 PRESCRIBED EXPERIMENT 2: ACID-BASE REACTIONS 


                                 

WORK SHEET 
TOTAL MARK: 50

ACTIVITY

Titration of oxalic acid against sodium hydroxide to determine the concentration of the sodium hydroxide.

In this investigation you will prepare an acidic solution accurately and thus you will know its exact concentration. You will then react this acid with a base of an unknown concentration to determine the concentration of the base.

What you will need:

Erlenmeyer flasks,
Burettes,
Burette clamp,
Medicine  dropper,
Retort stand,
White tile /paper,
Measuring cylinders,
Mass meter		Oxalic acid,
Sodium Hydroxide,
Phenolphthalein as indicator,
Funnel,
Beaker,
Spatula,
Glass rod,
Pipette with sucker

What to do:

  1. Prepare a standard solution of oxalic acid which has a concentration of approximately 1mol.dm-3.
  2. Now prepare a sodium hydroxide solution by dissolving approximately 2g of dry sodium hydroxide in 500ml of water.
  3. Add two drops of the indicator solution.
  4. Place the burette in the clamp.
  5. Using the funnel, fill the burette to above zero mark with the acid solution.
  6. Then, holding the beaker, with which you used to pour the acid, beneath the burette, gradually open the tap.
  7. Allow the level of the base to come down to exactly zero (reading from the bottom of the meniscus).
  8. Pipette using the sucker exactly 25ml of oxalic acid solution in a volumetric flask.
  9. Add a few drops of phenolphthalein to the acid.
  10. Hold the conical flask beneath the burette with your right hand and gradually open the tap with your left.
  11. Swirl the conical flak continuously and watch it closely for the first sign of a colour change.
  12. As you see that you are approaching the point of neutralization, close the tap slightly so that you are adding drop by drop.
  13. When the colour changes completely the titration is finished.
  14. Close the tap and read from the burette how much acid was used.
  15. Repeat this procedure at least twice so that you have three readings for the volume of NaOH (of unknown concentration) required to neutralize exactly 25ml of oxalic acid (of known concentration).
  16. Take an average of these three and use it to calculate the concentration of the NaOH.
  17. Now calculate the concentration of the sodium hydroxide solution.
  18. Make a neat labeled sketch to represent the apparatus
  19. Now write a report using the format learnt in class.

     Questions

  1. What is the appropriate concentration of NAOH (2g in 500ml of water)
  2. Calculate the theoretical concentration of NaOH from the actual mass of NaOH you measured.
  3. How does your theoretical value for NaOH concentration (from the actual mass you measured) differ from the actual concentration you calculated (from the titration procedure)? Can you think of some reasons why your values may differ?
Chipa Maimela GRADE 12 PHYSICAL SCIENCES, GRADE 12 QUESTION PAPERS, PHYSICAL SCIENCES GRADE 12

Grade 12 p1 September 2020 FS