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Titration procedure:

1. Prepare a solution from an accurately weighed sample to +/- 0.0001 g of the material to be analyzed.
2. Choose a substance that will react rapidly and completely with the analyte and prepare a standard solution of this substance. The concentration of the standard solution should be known to +/- 0.0001 M.
3. Place the standard solution in a buret and add it slowly to the unknown. This process is called titration and the solution in the buret is called the titrant. Continue the titration until the reaction is complete; that is, until the amount of reactant added is exactly the amount required to react with all the constituent being analyzed. This point is called the equivalence point, and can be detected by adding an indicator to the unknown solution before beginning the titration. An indicator is a substance that gives a color change at or near the equivalence point. The point at which the color change occurs is the end point of the titration.
4. Measure the exact volume of standard solution required from buret readings before and after the titration. Since the molarity of the standard solution is known, the number of moles of titrant can be calculated. From a knowledge of the equation for the reaction, the number of moles of constituent present in the sample can also be calculated.
5. The most accurate and convenient way of preparing a standard solution is to weigh the reagent, dissolve it, and dilute the solution to a definite volume in a volumetric flask. This method can only be used if the reagent is a primary standard.
6. In order for a reagent to be a primary standard, it must be obtainable in pure form (generally at least 99.98% pure), stable both in pure form and in solution, easy to dry and keep dry, and soluble in a suitable solvent.
7. Many useful reagents do not meet those requirements, so the reagent is dissolved and diluted approximately to the concentration desired. The solution is then standardized by titrating it against a primary solution. This standardized soluton is called a secondary standard.
8. Clean the buret before use and rinse with water. If any drops of water collect on the walls, the buret is not clean. Once the buret is clean, rinse it with the titrant solution before filling it. Pour about 5 mL of the titrant into the buret and, holding the buret almost horizontally, rotate it slowly so that the titrant cleans the entire buret. Do this three times.
9. Place the buret in a buret clamp attached to a large ring stand. Using a funnel, fill the buret with titrant to a level above the zero mark. Place a beaker under the buret and open the stopcock for a few seconds to remove all air from the tip and fill it. The top of the solution should now be below the zero mark.
10. Read the buret to +/- 0.01 mL with the meniscus level with the eye to minimize parallax (see Fig. 1). Parallax is the varying of the apparent position of the meniscus due to eye level. If you are looking down on the meniscus, the reading will be low. If you are looking up at it, the reading will be high.
11. Place the solution that is to be titrated in an Erlenmeyer flask and add 3-5 drops of the appropriate indicator. Position the flask under the buret.
12. Add the titrant slowly from the buret while swirling the contents of the flask to assure adequate mixing (see Figure 2). As the end point is approached, the titrant must be added very slowly – a drop at a time. Usually there is an indication as the end point is approached. If the end point is a color change, the change is produced momentarily where the reagent drops into the solution, but fades with stirring into the solution. This fading occurs more slowly as the endpoint is approached.
13. When the end point has been reached, allow the solution to sit for 10 seconds so the liquid in the buret can settle, then read the buret. Subtract the initial buret reading from the final reading to obtain the volume of titrant used.

Once the titration is completed, the final calculations can be done.

Example

• A 25 ml solution of 0.5 M NaOH is titrated until neutralized into a 50 ml sample of HCl. What was the concentration of the HCl?
• Step 1: Determine [OH-]
•  Every mole of NaOH will have one mole of OH-. Therefore [OH-] = 0.5 M.

Step 2: Determine the number of moles of OH-

•     Molarity = number of moles/volume
•     Number of moles = Molarity x Volume
•     Number of moles OH- = (0.5 M)(0.025 L)
•    Number of moles OH- = 0.0125 mol

Step 3: Determine the number of moles of H+

•  When the base neutralizes the acid, the number of moles of H+ = the number of moles of OH-. Therefore, the number of moles of H+ = 0.0125 moles.

Step 4: Determine the concentration of HCl

•    Every mole of HCl will produce one mole of H+; therefore, the number of moles of HCl = number of moles of H+.
• Molarity = number of moles/volume
• Molarity of HCl = (0.0125 mol)/(0.05 L)
• Molarity of HCl = 0.25 M
• The concentration of the HCl is 0.25 M.

Another Solution Method

• The above steps can be reduced to one equation:
•                   Macid  X Vacid = Mbase X Vbase
• where
• Macid = concentration of the acid
• Vacid = volume of the acid
• Mbase = concentration of the base
• Vbase = volume of the base

This equation works for acid/base reactions where the mole ratio between acid and base is 1:1. If the ratio were different, as in Ca(OH)2 and HCl, the ratio would be 1 mole acid to 2 moles base. The equation would now be:

• MacidVacid = 2MbaseVbase
• For the example problem, the ratio is 1:1:
• MacidVacid = MbaseVbase
• Macid(50 ml)= (0.5 M)(25 ml)
• Macid = 12.5 MmL/50 ml
• Macid = 0.25 M

Sources of errors in volumetric analysis

(a) solution not made homogeneous

These results from the solution not being thoroughly mixed  by shaking or swirling

• Inaccuracy in instruments used ; some instruments have errors  caused by manufacturing eg due to poor calibration   
• Errors in weighing
• These may result as a result of carelessness or lack of concentration by the technician.
• Presence of impurities in chemicals used.

These are due to contaminants or impurities on chemicals used  which may arise  due to action of moisture , light , dust particles  ,or oxygen . These can be minimized  by correct storage

(d) Inaccuracy in endpoint recorded.

These may occur if too much indicator is used , an extra amount  of reagent  may be  needed  to cause color change .It is helpful to perform a blank titration  so as to ascertain  the volume of the reagent  that is necessary  to affect the indicator  which have been added  to a volume of water  approximately  equal  to the final volume  of solution  likely to be obtained  in the actual titration . These  problem can be overcome by practice and experience.

NB; The result obtained in volumetric analysis is correct to three decimal places