Titration Guidelines

Titration Guidelines

Rinsing the Pipette:

A pipette is used to measure and transfer a precise volume of liquid. You rinse a pipette with the solution whose volume you are measuring. This ensures that the solution will not be diluted or contaminated.

1. Pour a sample of standard solution into a clean, dry beaker.

2. Place the pipette tip in a beaker of distilled water. Squeeze the suction bulb. Maintain your grip while placing it over the stem of the pipette. Do not insert the stem into the bulb. 

3. Relax your grip on the bulb to draw up a small volume of distilled water.

4. Remove the bulb, and discard the water by letting it drain out.

5. Rinse the pipette by drawing several millilitres of solution from the beaker into it. Rotate and rock the pipette to coat the inner surface with solution. Discard the rinse. Rinse the pipette twice in this way. It is now ready to fill with standard solution.

NOTE: Never use your mouth instead of a suction bulb to draw a liquid into a pipette. The liquid could be corrosive or poisonous. As well, you would contaminate the glass stem.

Filling the Pipette:

6. Place the tip of the pipette below the surface of the solution.

7. Hold the suction bulb loosely on the end of the glass stem. Use the suction bulb to draw liquid

up just past the etched volume mark. (See Figure below)

8. As quickly and smoothly as you can, slide the bulb off and place your index finger over the end of the glass stem.

NOTE(a): Draw a bit more liquid than you need into the pipette. It is easier to reduce this volume than it is to add more solution to the pipette.

NOTE(b): The bottom of the meniscus must align exactly with the etched mark.

9. Gently roll your finger slightly away from end of the stem to let solution drain slowly out.

10. When the bottom of the meniscus aligns with the etched mark, as in Figure below, press your finger back over the end of the stem. This will prevent more solution from draining out.

11. Touch the tip of the pipette to the side of the beaker to remove any clinging drop. See Figure below. The measured volume inside the pipette is now ready to be transferred to an Erlenmeyer flask or a volumetric flask.

NOTE (A): We can prevent a “stubborn” drop from clinging to the pipette tip by touching the tip to the inside of the glass surface.

NOTE (B): Practice removing the bulb and replacing it with your index finger (or thumb). You need to be able to perform this action quickly and smoothly.

Transferring the Solution:

12. Place the tip of the pipette against the inside glass wall of the flask. Let the solution drain slowly, by removing your finger from the stem.

13. After the solution drains, wait several seconds and then touch the tip to the inside wall of the flask to remove any drop on the end. Note: You may notice a small amount of liquid remaining in the tip. The pipette was calibrated to retain this amount. Do not try to remove it.

Adding the Indicator:

14. Add two or three drops of indicator to the flask and its contents. Do not add too much indicator. Using more does not make the colour change easier to see. Also, indicators are usually weak acids. Too much can change the amount of base needed for neutralization. You are now ready to prepare the apparatus for the titration.

Rinsing the Burette:

A burette is a graduated glass tube with a tap at one end. It is used to accurately measure the volume of liquid added during a titration experiment.

15. To rinse the burette, close the tap and add about10 mL of distilled water from a wash bottle.

16. Tip the burette to one side, and roll it gently back and forth so that the water comes in contact with all inner surfaces.

17. Hold the burette over a sink. Open the tap, and let the water drain out. While you do this, check

that the tap does not leak. Make sure that it turns smoothly and easily.

18. Rinse the burette with 5 mL to 10 mL of the solution that will be measured. Remember to open the tap to rinse the lower portion of the burette. Rinse the burette twice, discarding the liquid each time.

Note: If you are right-handed, the tap should be on your right as you face the burette. Use your left hand to operate the tap. Use your right hand to swirl the liquid in the Erlenmeyer flask. If you are left-handed, reverse this arrangement.

Filling the Burette

19. Assemble a retort stand and burette clamp to hold the burette. Place a funnel in the top of theburette.

20. With the tap closed, add solution until the liquid is above the zero mark. Remove the funnel. Carefully open the tap. Drain the liquid into a beaker until the bottom of the meniscus is at or below the zero mark.

21. Touch the tip of the burette against the beaker to remove any clinging drop. Check that the portionof the burette that is below the tap is filled with liquid and contains no air bubbles.

22. Record the initial burette reading in your notebook.

23. Replace the beaker with the Erlenmeyer flask that you prepared earlier. Place a sheet of white paper under the Erlenmeyer to help you see the indicator colour change that will occur near the endpoint.

Note: Near the endpoint, when you see the indicator change colour as liquid enters the flask from the burette, slow the addition of liquid. The endpoint can occur very quickly.

Reading the Burette

24. A meniscus reader is a small white card with a thick black line on it. Hold the card behind the burette, with the black line just under the meniscus, as in Figure below. Record the volume added from the burette to the nearest 0.01 mL.

Figure :A meniscus reader helps you read the volume of liquid more easily

Note: Observe the level of solution in the burette so that your eye is level with the bottom of the meniscus.

By:-

Anjani Kumar Singh