Titration is a technique used in chemistry to determine the concentration of a reagent mixed with an unknown substance. If done correctly and carefully, a titration will give very accurate results.
Steps
Step 1. Get the items listed in the "Things You'll Need" section at the bottom of this article
Step 2. Rinse and clean the burette
Step 3. Clean and wash all glassware with tap water and, if necessary, with some detergent (if available, use demineralised water)
Handle burettes with care, as they are very fragile. Always hold them with two hands.
Step 4. Rinse all glassware with distilled water to minimize the likelihood of contamination
Step 5. Measure a precise amount of analyte (the reagent mixed with the unknown substance)
Step 6. Fill your beaker or flask with a small amount of distilled water
Step 7. Pour the analyte into your beaker or flask, making sure to pour it all the way out
Step 8. Add a small amount (4-5 drops) of the appropriate color indicator into the beaker
Step 9. Shake the contents by swirling the beaker
Step 10. Fill the burette with excess titrant (chemical that reacts with the analyte)
The titrant must be in aqueous form.
Step 11. Carefully secure the burette to a holder using pliers
The tip of the burette must avoid contact with any surface.
Step 12. Place the beaker under the burette
Step 13. Record the initial volume of the burette at the meniscus (the lowest part of the basin in the liquid)
Step 14. Turn the stopcock of the burette (the valve near the tip) vertically, so that the titrant is added to the beaker
Add only a small amount of titrant. A color change should occur. Shake the beaker until the color disappears.
Step 15. Repeat the previous step until the first shade of color appears (you can barely notice it, so be careful and go very slowly)
Step 16. Record the volume of the burette
Step 17. Add the titrant drop by drop as you approach the end point
Step 18. Shake the contents of the beaker after adding each drop
Step 19. Stop the operation when you have reached the end point, which is the point where the reagent within the analyte has been completely neutralized
You can understand that you have reached the end point when the color changes, based on the indicator you have chosen to use.
Step 20. Record the final volume
Step 21. Add drops of titrant until you pass the end point
At this point, after adding the titrant, the contents of the beaker should take on the color of the indicator used.
Step 22. Clean the glassware by wiping off the water and solution leftovers
Step 23. Eliminate used chemicals using a properly labeled waste container
Step 24. Calculate the concentration of the reagent within the analyte using the collected data
Advice
- The end point is extremely easy to get past, so be especially careful during the operation. At the slightest sensation of having reached the end point, start counting the drops and proceed very slowly.
- While reading, place your eyes at the same volume level from the burette - if your eyes are at a different level with each reading, your measurements will not be accurate.
- Concentration calculations should be made for the appropriate number of significant digits.
- It is easier to understand if the final point has been reached by inserting a white card under the flask, in order to check the color variation of the indicator.
- Handle the burette carefully - it can break easily.
- Remember to remove the funnel filter after adding the titrant to the burette, as it can prevent successful titration.
- Records the burette volume at a higher digit than the one provided (ex: burette readings are in the tens; consider the readings in the hundreds).
- Place a watch glass over the flasks of the water and the unknown substance; if they are left too long in contact with the air they can change the molarities.
- Place a small beaker on top of the burette, especially if you are titrating with sodium hydroxide (NaOH); if left in contact with air, part of the hydroxide (OH) will bind with the water molecules and the molarity of the sodium hydroxide solution will vary.
Warnings
- Do not ingest the reagents.
- Make sure you pour the entire analyte into the beaker. Any leftover analyte in the container will cause errors during the calculations.
- Don't pour chemicals down the sink; place them in a properly labeled waste container.
