## GRADE 12 PRESCRIBED EXPERIMENT 2: ACID-BASE REACTIONS

##### 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:

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.
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?

## Formal experiment 1: Heating and cooling curve of water

Aim

To investigate the heating and cooling curve of water.

Apparatus

beakers

ice

Bunsen burner

thermometer

water

Chipa Thomas Maimela‘s insight:

Method

Place some ice in a beaker.

Measure the temperature of the ice and record it.

After 1 minute measure the temperature again and record it. Repeat every minute, until at least 3 minutes after the ice has melted.

Plot a graph of time versus temperature for the heating of ice.

Heat some water in a beaker until it boils. Measure and record the temperature of the water.

Remove the water from the heat and measure the temperature every 1 minute, until the beaker is cool to touch.

Warning:

Be careful when handling the beaker of hot water. Do not touch the beaker with your hands, you will burn yourself.

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