SAINT MARY’S UNIVERSITY
Bayombong, Nueva Vizcaya, Philippines
SCHOOL OF HEALTH AND NATURAL SCIENCES
CENTER FOR NATURAL SCIENCES
Activity 1
INTRODUCTION TO THE ANALYTICAL BALANCE AND DESICCATOR
INTRODUCTION
The ability to determine mass accurately is fundamental not only to analytical
chemistry but also to all of modern science. Practically speaking, all measurements which
we shall perform in this course relate either directly or indirectly to a weighing using the
single pan analytical balance. This is a delicate and precise instrument which, if kept
scrupulously clean and handled correctly, will continue to yield reliable data during the
course of its usage. It is therefore imperative that you become rapidly acquainted with
your balance and that you gain assurance as to the correctness of your equipment and
technique before proceeding with other experiments.
Oven drying is the most common way of removing moisture from solids. This
approach is not appropriate for substances that decompose or for those from which
water is not removed at the temperature of the oven. The desiccator is used to store
dried samples in a dry atmosphere. It should not be used to dry an object, but to maintain
an already dried object indefinitely in a dry condition.
To minimize the uptake of moisture, dried materials are stored in desiccators while
they cool.
OBJECTIVE
This activity should enable you to accurately determine the mass of a sample using
an analytical balance and demonstrate proper use of the desiccator
PRE-LABORATORY
Answer or explain substantially what is asked. Cite your references.
1. Define mass.
Mass, denoted using m or M, is a dimensionless quantity representing the
amount of matter in a particle or object (Tech Target Contributor, n.d.).
Basically, it is a measure of the amount of matter in a substance or an
object. The basic SI unit (International System of Units) or metric system for
mass is kilogram (kg); smaller masses may be measured in grams (g).
2. What is the best tool to get mass?
In determining an object's (substance's) mass, a balance, specifically
analytical balance, is the best tool to be used. Analytical balance is a
highly precise and/or accurate laboratory balance for measuring masses.
Copyright 2021. All rights reserved. No parts of this document may be reproduced in any form or by any electronic means, including information
storage and retrieval systems, without permission in writing from the author, except by reviewers, who may quote brief passages in a review.
SAINT MARY’S UNIVERSITY
Bayombong, Nueva Vizcaya, Philippines
SCHOOL OF HEALTH AND NATURAL SCIENCES
Typically,
it FOR
is designed
with
an enclosed measuring pan to avoid the
CENTER
NATURAL
SCIENCES
influences of dust and air currents, and may include vibration resistance,
data transfer, automation, and capacity range options (Sartorius, n.d.).
3. Why is mass an important unit of measure in Chemistry?
Mass is important to measure because it will measure the amount of force
it will take to move the object. Mass is often measured by measuring an
unmeasured object with standardized forms of measurements such as
milligrams, grams and kilograms.
4. How can you assure accuracy in getting the mass?
In order to protect the balance and ensure accurate results, the following
ways should be properly observed:
 Always check that the balance is level before using;
 Do not weigh hot or cold objects;
 Clean up any spills around the balance immediately; and
 Never add chemicals or any unnecessary substances to a container.
Additionally, according to Huntress (2021), the following steps are essential
and practical to further ensure the precision and accuracy of mass (and
other laboratory results/data):
 Keep everything calibrated. Calibration involves adjusting or
standardizing equipment in the laboratory.
 Conduct routine maintenance. All lab instruments are needed to be
given regular care to operate at their maximum.
 Operate in the appropriate range with correct parameters. Use tools
that are designed and calibrated to work in the range you are
measuring. Once unsure of measurements, reach out to any trusted
peer or mentor for advice.
 Understand significant figures and record correctly. Keep significant
figures consistent when measuring items repeatedly, and ensure the
number of the same is appropriate for each measurement.
 Take multiple measurements.
 Detect shifts over time. Address the measurement drift issue
immediately by recalibration or preventative maintenance.
 Consider “human factor”. Ensure that procedures are kept up to
date, and that all lab personnel are properly-trained.
 Perform a measurement systems analysis). It mathematically
determines the amount of variation that exists when taking
measurements multiple times.
MATERIALS AND REAGENTS
Analytical Balance
Desiccator
Crucible Tongs
Crucibles with cover
Copyright 2021. All rights reserved. No parts of this document may be reproduced in any form or by any electronic means, including information
storage and retrieval systems, without permission in writing from the author, except by reviewers, who may quote brief passages in a review.
SAINT MARY’S UNIVERSITY
Bayombong, Nueva Vizcaya, Philippines
SCHOOL OF HEALTH AND NATURAL SCIENCES
Weighing
bottleFOR NATURAL SCIENCES
CENTER
Beaker
Salt
Procedures
A. General Guidelines for Using the Analytical Balance
1. Chemicals are never placed directly on the weighing pan. A weighing
boat, paper or bottle is used under the chemical.
2. Do not exceed the maximum weight limit of the balance.
3. Center the load on the pan as much as possible.
4. All objects or samples to be weighed must be in thermal equilibrium
with the room before a weighing can be attempted. Temperature
gradients within the balance case can result in convection currents,
and the resultant draft against the pan will lead to erroneous
weighing.
5. Never handle the item to be weighed directly with your fingers.
6. Immediately clean any chemical spillage on the pan, within the
weighing chamber, or in the work area surrounding the balance.
7. Always record weights to the nearest 0.0001 g.
Copyright 2021. All rights reserved. No parts of this document may be reproduced in any form or by any electronic means, including information
storage and retrieval systems, without permission in writing from the author, except by reviewers, who may quote brief passages in a review.
SAINT MARY’S UNIVERSITY
Bayombong, Nueva Vizcaya, Philippines
SCHOOL OF HEALTH AND NATURAL SCIENCES
8. CENTER
Leave the
sliding
glass doors
closed, the balance covered and the
FOR
NATURAL
SCIENCES
area around it clean.
9. Attend a demonstration by your instructor on how to operate the
balance, and how to handle objects for weighing.
B. Determining the Mass of an Object
1. Obtain a known sample from your lab instructor and record the sample
identification number. Your sample contains five pellets of one color
and ten of another.
2. Weigh each to 0.1 mg, recording your data in your laboratory
notebook. Do not touch them with your fingers, as skin oils may change
the mass of the pellets. Use tweezers or lintless paper or weighing paper
to handle the pellets.
3. Reweigh the known sample 4 times.
C. Weighing Out a Dispersible Sample
The simplest and most effective method of weighing out samples is by
difference. One approach is to first find the total weight of your sample
container and its contents, pour or shake some of this material out into a
labelled beaker or flask and finally reweighing the sample bottle plus
remaining material. The difference between the initial and final weighing
represents the sample mass. An alternative approach is to weigh the empty
container, add the sample to the container, record its mass, and then
quantitatively transfer its contents to a flask or beaker. The mass of the sample
is the difference between the weight of the container plus contents minus
the weight of the container. The object of this section will be to compare
these two approaches.
1. Fill your clean, dry weighing bottle about 1/8 full with reagent grade
NaCl. Be careful not to get material on the stopper.
2. Weigh the weighing bottle with NaCl to the nearest 0.1 mg.
3. Weigh a clean, dry 50 mL beaker to the nearest 0.1 mg. into the
beaker on the balance pan, deliver 0.50 ± 0.01 g to the nearest 0.1
mg. of the NaCl from the weighing bottle. Record the final weight of
the beaker.
4. Weigh the weighing bottle with residual sample. Compare the mass
of NaCl added to the beaker with the mass of NaCl removed from
the weighing bottle.
5. Weigh a clean, dry and empty weighing bottle.
6. Into the weighing bottle on the balance pan, deliver 0.250 ± 0.005 g
to the nearest 0.1 mg. of the NaCl.
7. Record the final weight of the beaker. In the event that you spill NaCl
onto the balance pan, arrest the balance, clean the pan and then
repeat steps 6 and 7
D. Using the Desiccator
1. To open - slide lid horizontally across the top to one side until it comes off. Use
one hand to hold the bottom of the desiccator while using the other hand to
grasp the knob.
Copyright 2021. All rights reserved. No parts of this document may be reproduced in any form or by any electronic means, including information
storage and retrieval systems, without permission in writing from the author, except by reviewers, who may quote brief passages in a review.
SAINT MARY’S UNIVERSITY
Bayombong, Nueva Vizcaya, Philippines
SCHOOL OF HEALTH AND NATURAL SCIENCES
2. To close
- place
lidNATURAL
partly onSCIENCES
the top and slide across until desiccator is
CENTER
FOR
completely closed and then rotate lid gently in both directions.
3. Do not attempt to lift lid off vertically.
4. Make sure the lid has enough grease around the ground glass rim - if necessary,
spread Vaseline uniformly on the rim. When the lid is improperly seated, the
greased rim will appear as shown in Figure 3. On the other hand, when the lid
is properly seated, the greased rim will appear.
5. If the desiccant appears wet or clumpy, it probably needs to be replaced with
new desiccant. It is helpful to have a small amount of indicating desiccant
present. When the color changes to pink, the desiccant should be replaced.
6. Desiccants should be handled in the hood and added carefully. Desiccant
should not coat the sides or plate of the desiccator.
7. When placing a heated object in a desiccator, allow some cooling to occur
before the lid is seated.
8. Transfer to and from the desiccator should normally not be by fingers but by
crucible tongs or by strips of lintless paper.
9. It is also helpful to break the seal once or twice during cooling to relieve any
excessive vacuum that develops.
10. Finally, lock the lid in place with your thumbs while moving the desiccator from
one place to another.
DATA AND RESULT
1. Draw or print and label the parts of an analytical balance and desiccator.
Copyright 2021. All rights reserved. No parts of this document may be reproduced in any form or by any electronic means, including information
storage and retrieval systems, without permission in writing from the author, except by reviewers, who may quote brief passages in a review.
SAINT MARY’S UNIVERSITY
Bayombong, Nueva Vizcaya, Philippines
SCHOOL OF HEALTH AND NATURAL SCIENCES
CENTER FOR NATURAL SCIENCES
2. Demonstrate how to properly use the desiccator
To open the desiccator, slide the lid gently as shown at left. If you
feel or hear metal scraping against metal when you slide off the lid, then a
small amount of silicon grease needs to be rubbed around the flat surface
of the lid. Squeeze quite small amount of grease onto your finger, as at the
right, and rub it all around the flat surface of the lid. The desiccator contains
a plate with holes over a screen which covers granulated anhydrous
calcium sulphate, a desiccating or dehydrating agent. The desiccator
ought not to be left open except to transfer samples in or out of it. (Hills,
2022)
The following are the steps or key concepts to remember in properly
utilizing a desiccator:
 Slide the cover horizontally with a gentle force until it starts moving.
Grasp the knob with one hand, and with the other hold the base
and apply more force to take it off completely;
 Do not get tempted to lift the desiccator by lifting the top knob.
Always lift with both hands holding the bottom and the cover;
Copyright 2021. All rights reserved. No parts of this document may be reproduced in any form or by any electronic means, including information
storage and retrieval systems, without permission in writing from the author, except by reviewers, who may quote brief passages in a review.
SAINT MARY’S UNIVERSITY
Bayombong, Nueva Vizcaya, Philippines
SCHOOL OF HEALTH AND NATURAL SCIENCES
 To close,
lid gently
on top and close slowly by applying a mild
CENTER
FORplace
NATURAL
SCIENCES
force till it closes. Rotate lid gently in both directions to ensure an
airtight seal;
 Ensure that the rim does not run out of grease but at same time do
not use an excessive amount of grease. A thin uniform film is usually
sufficient;
 Keep the lid upside down on removal but away from the workbench
edge to prevent rollover; and
 Place a hot substance carefully inside after removal from the hot air
oven. Keep the crucible with the lift ajar for a couple of minutes and
then close the lid by sliding it to expel hot air so that the lid does not
get blown out due to expansion of hot air and also prevent vacuum
formation later which can make opening difficult.
GUIDE QUESTIONS
1. List possible reasons for any discrepancy. Suggest ways to test your hypotheses.
2. Describe the determinate and indeterminate errors in an experiment.
Prepared by:
Olivar Reimos D. Barroga
Instructor
Submitted to:
Regidor Almendral
Instructor
Submitted by:
Allen Zyrix H. Espiritu
Kevin Rye E. Perez
Richelle Mateo
Devalene P. Walat
BSMLS 1C
Copyright 2021. All rights reserved. No parts of this document may be reproduced in any form or by any electronic means, including information
storage and retrieval systems, without permission in writing from the author, except by reviewers, who may quote brief passages in a review.