For any piece of analytical equipment and glassware to provide precise and accurate results proper use and technique is essential. The purpose of this manual is to review this equipment and the necessary techniques.

Analytical Balances
Analytical Glassware
Volumetric Pipets

Using Analytical Balances:
Steps to be followed in Weighing by Addition:

Fig. 1 Analytical Balance

Fig. 2 Horizontal-level bubble gauge

1. Check to ensure that the horizontal position of the balance is level. Each balance is equipped with a level indicator.
See Fig. 2. If not level see instructor.

2. Clean the balance pan with a brush.

3. Place a weighing boat, small beaker may also be used, on the centre of the balance pan and be sure to close the balance doors.

4. Tare the balance and wait until it reads zero grams.

5. Remove the weigh boat from the balance. Gently add solid sample to the weighing boat. Never add reagent while the weigh boat is in the balance!!!

6. Return the weigh boat to the balance and close the balance door. Record the weight to the nearest tenth of a milligram, i.e., four places after the decimal.

7. Remove the boat and sample. Transfer the sample to the appropriate piece of glassware.

Steps to be followed in Weighing by Difference:

This technique is useful when several duplicate masses of a material must be weighed out.

1. Check to ensure that the horizontal position of the balance is level. Each balance is equipped with a level indicator.
See Fig. 2. If not level see instructor.

2. Clean the balance pan with a brush.

3. Place a weighing boat on the centre of the balance pan and be sure to close the balance doors.

4. Tare the balance and wait until it reads zero grams.

5. Remove the weigh boat from the balance. Place approximately 1-4 grams of the material to be measured into the weighing boat. Never add reagent while the weigh boat is in the balance!!!

6. Return the weigh boat to the balance and close the balance door. Record the weight to the nearest tenth of a milligram, i.e., four places after the decimal.

7. Carefully remove some material from the weigh boat and place it in an appropriate container. Reweigh the weigh boat. The difference between the original weight and the final weight is equal to the weight of sample taken. Repeat as necessary.

Be sure to avoid the following common mistakes when using either the analytical or trip balance (where applicable).
a)         Handling weighing bottles with bare fingers.
b)         Weighing damp or dirty objects.
c)         Leaving balance doors open.
d)         Leaving weights on the balance when finished.
e)         Forgetting to turn off the balance.
f)          Removing the object from the pan while the balance is still on.
g)         Weighing an object which is above room temperature.



In many laboratory experiments small amounts of reagents must be dispensed not only very accurately but also with a great deal of precision. In analytical experiments precise amounts of reagents are dispensed using glassware diagrammed in Fig. 3.

Graduated cylinders are the least precise of the analytical glassware but are suitable for most applications and there ease of use makes them a valuable piece of analytical glassware.



Volumetric Pipet

Measuring Pipet

Volumetric Flask

Graduated Cylinder

Fig. 3 Analytical glassware.

Pipets and burets must be kept absolutely clean in order to retain proper calibration. It is good practice in general to see that all glassware is absolutely clean. To test for cleanliness, fill the object with water and then empty it.  If the remaining water forms a uniform thin film on the walls with no beads, the object is clean.

To clean burets rinse repeatedly with distilled water(DW). Your buret has a Teflon bore stopcock: loosen the buret nut slightly to prevent freezing during storage.

Pipets and burets with hard-to-remove residues must be cleaned using soap and water. A buret brush may be used for cleaning a buret. Take care not to scratch the insides of the buret. Rinse well with distilled water after cleaning or use. Always rinse pipets well with distilled water after use and store them flat.


Use of Pipets:

Pipets are calibrated to deliver (TD) a measured volume of a liquid.

Two types are commonly used in chemistry laboratories: volumetric (or transfer) pipets and measuring pipets. See Fig. 4.

Fig. 4. Volumetric and Measuring Pipets.

As the above diagram shows, a volumetric pipet has one calibration mark and is designed to deliver one fixed volume. Various capacities (i.e. 5 mL, 20 mL, 50 mL etc.) are available and are accurate to two digits after the decimal. The pipet shown above is calibrated to deliver exactly 10 mL at 20° C and should be recorded as 10.00 mL.

Measuring Pipets include Serological and Mohr pipets. They deliver various volumes to varying degrees of accuracy. The measuring pipet is calibrated along its length: either straight to the tip or along the straight part of the pipet only. These pipets are usually not as accurate as volumetric pipets. Both measuring pipets shown below are calibrated as "10 in 1/10" which means the pipet delivers a maximum of 10 mL and is calibrated in 0.1 mL divisions. Volume measurements should be recorded to two digits after the decimal.

The Mohr pipet is calibrated to deliver to the 10 mL baseline. The tip cannot be allowed to drain. The Serological pipet is usually calibrated to deliver the tip.

1. Squeeze the air out of the pipet bulb and press the opening of the bulb against the opening of the pipet. Do not push the pipet into the bulb. The tip of the pipet must be kept under the surface of the liquid the entire time suction is applied or air will be sucked into the pipet.

2. Rinse the pipet well with at least two portions of the desired solution.

3. Fill the pipet above the calibration mark using a pipet bulb.

4. Quickly remove the bulb and place your index finger (not your thumb) over the end of the pipet.

5. Wipe the pipet tip clean of any excess solution.

6. Drain the solution in the pipet down to the calibration mark by gently reducing the pressure of your index finger. You do not have to remove your index finger. Tip the pipet against the beaker to remove any excess solution. If your finger "leaks" and allows the level in the pipet to drop below the calibration line, moisten your finger slightly and try again.

7. Reset the pipet tip against the wall of the container into which the solution is to be transferred and allow the solution to drain.  Volumetric pipets are allowed to drain completely. Measuring pipets should not be allowed to go past the desired volume levels. Leave the pipet in this position for at least 10 seconds after all the solution appears to have drained out and touch the pipet tip to the side of the flask to remove any droplets. Remove the pipet. DO NOT  BLOW OUT THE SOLUTION REMAINING IN THE PIPET.

8. Rinse the pipet well with DW and store it when finished.


Use of Volumetric Flasks:

Fig. 5 250 mL Volumetric flask.

Volumetric flasks are available with capacities ranging from 5 to 5000 mL They are normally calibrated to contain (TC) a specified volume at 20° C. The volumetric shown above is calibrated to contain exactly 250 mL at 20° C and should be recorded as 250.00 mL.

The calibration mark is a ring around the narrow neck of the flask. A volumetric flask is used for making a solution whose concentration must be exactly known.

Some volumetric flasks have two calibration marks, TC and TD.  The TD mark is above the TC mark and includes the amount of solution that remains on the wall of the flask when emptied. All TD volumetric ware is calibrated to take into account the film of solution that remains on the vessel walls.  This is the reason that correct calibration is maintained only with clean glassware.

Volumetric flasks are properly filled when the bottom of the solution meniscus is exactly at the calibration mark. Always read or adjust the solution level in your glassware with your eye exactly level with the meniscus. This avoids a parallax error. On your buret use the calibration marks that completely encircle the buret to estimate when your eye is level with the meniscus.  Estimation of the meniscus bottom can be aided by placing a white card with a black line drawn horizontally across it behind the glassware and bringing the black line up to the meniscus.

1. Solid reagent (the solute) is transferred to the volumetric flask by using a funnel. The weighing boat is rinsed with the solvent used (usually distilled water) into the funnel. Then the funnel is rinsed with solvent while still inserted in the flask so that any remaining solute particles will be washed into the flask. In this way, the solute is transferred quantitatively - nothing is left behind.

2. After the solute has been added, the flask should be filled about halfway, and then swirled until all the solute has dissolved. Then solvent is added near to the calibration mark but not up to it.

3. Final addition is accomplished using a medicine dropper. If the liquid level goes past the calibration mark the solution must be discarded. Make sure your eyes are level with the liquid surface, and add solvent drop-wise until the bottom of the meniscus is touching the calibration line. It is important that the solution is well mixed. Stopper and invert the flask several times.

When using a volumetric flask to prepare a solution from a solid or pure liquid, it is usually best to weigh the desired substance by difference into an ordinary beaker. Dissolve the substance in the beaker with pure solvent (usually distilled water) being careful not to splash any solution out of the beaker. Transfer this solution to the volumetric flask quantitatively using a funnel. To avoid any solution running down the outside of the beaker, place a stirring rod across the top of the beaker. This rod should fit into the pouring depression on the beaker and extend about 1 cm beyond the lip. Use this rod to guide the solution into the flask. Rinse the beaker three times with solvent and transfer these rinses to the flask in the same manner. Fill the flask at least 95% full by adding solvent and mix thoroughly. Add enough solvent carefully and slowly to bring the solution level with the calibration mark using a medicine dropper for the last few drops. Again shake well to mix thoroughly. Never dilute to the mark if the solution temperature differs significantly from room temperature.


Use of Burets:

Fig. 6 Diagram of a buret.

A buret is a glass tube with graduations that can be used to determine the volume of a solution added to a receiving vessel.

A buret is calibrated to be read from the top down.  For example, a 25 mL buret will have the zero mark at the top and 25 mL mark at the bottom, above the stopcock.  To determine the volume dispensed from the buret, use the graduation that is closest to the lowest point of the meniscus.  As an example, in the diagram, the meniscus is between the 11.4 and 11.5 mL marks. Thus the column of liquid dispensed would be recorded as 11.45 mL, assuming that the titration was begun at zero.

Using a buret is not difficult, however, good technique is needed to titrate accurately.

1. Be sure the buret is clean by rinsing several times with DW. Drain the buret well and rinse at least twice with the desired solution and discard the washings.

2. Fill the buret and drain to or below the 0.00 mL mark.

3. After a suitable time for drainage along the walls, wipe any excess solution from the buret tip and be sure that no air bubbles are trapped in either the tip or on the sides of the buret. If air bubbles are present in the tip, open the stopcock completely to force them out.  If there are air bubbles on the sides of the buret, gently tap the buret to get them to rise to the surface. Read the buret to 2 places after the decimal.

4. Deliver the required amount of solution and read the buret again. If you have emptied the buret rapidly, wait for the solution on the walls to drain before making a reading.

5. During titrations the titrant, solution in the buret, should be added slowly to the titrated solution.  A flow rate of 1-2 drops per second is recommended. It is essential that the titrant be mixed thoroughly with the solution being titrated throughout the titration.  Be sure to stir or swirl the solution into which the titrant is being added to insure complete mixing of the constituents.

6. When approaching the end point of a titration with a colour change that is not sharp, note down the volume and colour after each addition to avoid overrunning the endpoint. Approach the end point of all titrations with extreme care. After each addition contact the buret tip with the wall of the titration vessel to remove any drop of titrant remaining on the tip and be sure to wash down the sides of the receiving vessel.

7. Always estimate the  buret reading to 0.01 mL.

8. When finished, rinse the buret well with DW.