A titration is a technique used in chemistry to determine the concentration of a reagent mixed with an unknown solution. The process involves adding a known solution to an unknown solution until a reaction occurs. Most often, the reaction is a change in color. When done correctly and carefully, a titration provides very accurate results for acid-base calculations, redox reactions, complex formation, and many other calculations.
Steps
Part 1 of 3: Prepare the Equipment
Step 1. Gather all the necessary equipment before you begin
Carrying out a degree requires having all the necessary elements before starting. Make sure you have a calibrated burette with its holder, several beakers or Erlenmeyer flasks, a measured amount of the analyte, and a large amount of titrant. While not a requirement, having a magnetic stir plate is very helpful.
- The analyte is the sample in which you will look for a specific chemical quantity, called a titrant. For example, if you want to check the chloride values in your local water supply, tap water will be your analyte, and chloride will be the titrant.
- Titrant is the chemical that you will add to the analyte in measured amounts to calculate the amount of titrant.
- It is important that you have enough titrant to be able to repeat the titration at least three times. If you don't know how much titrant you need, do an online search or ask your lab manager.
Step 2. Clean and sterilize the burette
To have an accurate reading of the titration, the burette must be completely clean. Sterilize it completely to remove any solutions from previous uses. Then close the valve (which is near the tip) and fill the burette with deionized water. Turn it a few times before opening the valve and allowing it to drain.
- Repeat the cleaning process at least three times with water to thoroughly clean the burette.
- After rinsing the burette with water, perform the same rinsing procedure at least twice with the analyte.
Step 3. Clean and rinse all glass elements
Rinse any glass items you plan to use, such as beakers or flasks, with deionized water. Depending on what the glass elements have been previously used with, you may need to wash them with a mild detergent. Then rinse them all with distilled water and allow them to dry completely.
If you don't have deionized water, use tap water. However, it is necessary to rinse the materials with distilled water to reduce the chances of analyte contamination
Step 4. Fill the buret with a large quantity of titrant
The titrant must be in liquid form. Pour it to the zero point of the burette using a graduated cylinder, small flask or beaker.
If you overfill the burette, open the valve a little and allow the excess titrant to sink down to the zero mark
Step 5. Hold the burette carefully in the holder
The burette must be secure enough so that it does not move or slide. However, slowly tighten the clamp to prevent the burette from cracking or breaking. Make sure there is enough space between the tip of the burette and the bottom of the beaker or flask holder.
Step 6. Tap the burette to remove air bubbles
With the burette on its holder, gently tap it with your index finger to remove any gas bubbles within the liquid. Then record the initial volume of the burette at the level of the meniscus (the lowest part of the curve in the liquid).
Part 2 of 3: Perform the titration
Step 1. Measure a precise amount of analyte into a clean beaker or flask
You must know exactly how much analyte you will use in order to calculate the final concentrations. Use a pipette to measure the required amount of analyte in the beaker.
- If necessary, first rinse the analyte in the beaker or flask to ensure that only analyte is there.
- The amount of analyte you need will depend on the experimental design, the type of chemical, and the titrant to be determined.
Step 2. Pour a small amount of the color indicator into the beaker
Many titrations require the addition of a color or tint indicator before adding the titrant. The specific type of indicator you need will depend on the titrant you are looking for.
Also, the amount of color indicator you need will depend on the volume of the analyte. Generally, you will need three to five drops of indicator per 100 ml of analyte
Step 3. Add the second chemical, if necessary
While not all titration experiments require a second chemical, some do. The second chemical is often referred to as a chemical buffer. If the titrant requires one, use a pipette or measuring dropper to add it to the analyte after adding the color indicator.
- As with the color indicator, the amount and type of chemical buffer you need will depend on the amount of analyte and titrant you are looking for. However, you will generally need to add it until it removes the tint caused by the indicator.
- Generally, the chemical buffer solution will be acidic or alkaline in a known and specific concentration.
Step 4. Shake the beaker with a magnetic stir plate
If you have a magnetic stir plate, put the beaker inside and insert the stirrer into it. Slowly rotate the plate until the shaker begins to move enough to mix the solution in the beaker without splashing the walls of the beaker.
- You should leave the magnetic stir plate turned on until the titration is complete.
- If you don't have a magnetic stir plate, you can shake the beaker with your hands by gently swirling it four to five times before placing it under the burette.
Step 5. Place the beaker under the burette
The burette must be centered over the beaker. The tip should not touch the walls of the beaker.
Step 6. Slowly open the valve so that the titrant begins to drip
The titrant should go down one drop at a time. Allow it to drip into the analyte until a color change is observed in the solution in the beaker. The color change can be subtle, so proceed slowly and observe carefully.
- If you notice a change in color, close the valve and allow the agitator to run for 30 seconds. If the color dissipates before 30 seconds, open the valve slightly and continue adding the titrant drop by drop until a permanent change is obtained.
- If you're not using a magnetic stir plate, close the valve once you see the first flash of color change. Shake the glass to see if the color dissipates. If so, replace the beaker under the burette and continue the titration. Otherwise, you will have reached the end of the experiment.
Step 7. Record the final volume of the burette
Once you reach the end of the titration, close the valve and record the final volume of the titrant in the burette. Subtract the final volume from the initial volume to find the total volume of titrant added.
When reading the final volume of the burette, make sure your eyes are at the level of the meniscus. Take the measurement from there
Part 3 of 3: Finish the Analysis
Step 1. Dispose of used chemicals in a labeled waste container
Once the titration is complete, empty the beaker, burette, and any glassware you used into the appropriate containers. If you don't know what they are, ask your instructor or lab director.
Step 2. Rinse the glass elements with water to clean them
If possible, use deionized water to rinse the glass elements. If you don't have it, use tap water. Stir the water in the glasses and jars a few times before draining them. Repeat the rinse two or three times for each piece of glass.
To clean the burette, fill it with water, open the valve, and allow it to drain completely. Repeat the process two or three times to rinse the burette
Step 3. Calculate the concentration of the titrant
Each type of titration requires a different calculation to determine the concentration of the titrant in the analyte. Perform titration calculations or review the titration curve for the specific titrant to quantify the results.
Concentration calculations should be performed to the appropriate number of significant figures. If you're not sure, check with your instructor or lab directory
Advice
- You should always wear protective gloves and glasses, and have an emergency kit at hand when doing any type of degree.
- It's very easy to miss the final point if you're not paying attention. When you have the feeling that you are approaching the end point, start counting the drops and proceed slowly.
- In some cases, it is easier to determine the end point by holding a white paper under the beaker or flask to see if the indicator has changed color.
- Record the volume of the burette by subtracting a digit from the reading provided, if possible. For example, if the burette has readings to the nearest tenth, record the observation to the nearest hundredth.
Warnings
- Do not consume any of the reagents.
- Don't rinse chemicals down the sink. Instead, pour them into an appropriate, labeled waste container.