Laboratory Instruments

A laboratory is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed.

Labs used for scientific research take many forms because of the differing requirements of specialists in the various fields of science and engineering.

Laboratory equipment is generally used to either perform an experiment or to

take measurements and gather data. Larger or more sophisticated equipment is

generally called a scientific instrument.

Just as a business person has an office and a crafts person has a shop, a scientist

has a laboratory. Like any other workspace, a laboratory holds the tools of the

trade. The apparatus found in any given laboratory will vary based on the field of

research and level of the researchers, such as high school, collegiate or

professional. Most general purpose laboratories will contain key pieces of

apparatus, such as microscopes, beakers, and Bunsen burners.

Instruments and their uses

1. Volumetric and Heating Equipment

Beakers

A beaker is a cylindrical glass or plastic vessel used for holding liquids. It is a

multipurpose piece of equipment used for containing a chemical reaction,

measuring liquids, heating them over a Bunsen burners flame or collecting them in

a titration experiment.

Beakers serve multiple functions in a laboratory. They can be used to contain a

small chemical reaction. In experiments that yield a liquid product, beakers are

used to catch the liquid.

Erlenmeyer flask

Is a round bottom flask, which has a conical structure in the upper area and a

mouth with a narrow neck. It is mainly used for the preparation of solutions.

When people say Erlenmeyer flask, they are talking about a graduated flask

containing marks that indicate a certain volume. There are Erlenmeyer flasks in

different capacities.

Advantages of use

It is safer than a beaker, since the structure of the flask prevents loss of

substance contained solution (agitation or evaporation)

It is ideal for stirring solutions.

It can be easily cover with cotton or lid.

Volumetric Flask

They are glass containers with flat bottom and long, narrow neck, with a

capacity that denotes where to make the mark, which indicates a volume with high

accuracy and precision. In the same way that the pipettes, the neck of the flask is

built relatively thin, so that a small change in volume of the liquid causes a

considerable difference in the height of the meniscus; consequently the error by

adjusting the meniscus in the brand is very small.

Volumetric flasks are calibrated to contain the specified volume of liquid at a

definite temperature. As graduation surrounds the neck of the flask is easy to avoid

parallax errors when the liquid is brought to the mark, aligning the eye so that the

nearest and farthest ring sides are tangent to the bottom edge of the meniscus.

It is essential that the flask is free of fat, especially in signal measurement or

near to this. Volumetric flasks are used to prepare solutions of known

concentration to exact dilutions.

Utilization

1. Weigh or measure the required substance amount and transfer it to the flask.

2. Fill the flask with the minimum amount sufficient to dissolve or dilute the

substance transferred to it (the height of the liquid should not exceed half of the

height of the widest part).

3. Stir in circles to ensure that the substance is completely dissolved.

4. Continue filling the flask to about an inch below the capacity.

5. Dry the inside wall of the flask neck with a piece of absorbent paper placed

around a glass rod, taking care not to touch the solution.

Pipette

Pipettes allow transfer of generally no more than 20 ml of one vessel to another

volume, accurately. This allows measurement of fluid aliquots quite accurately.

They tend to be glass, but there are also plastic.

Classification of pipettes

Graduated pipettes: They are calibrated in convenient units to allow the transfer of

any size from 0.1 to 25 ml. They make possible the delivery of fractional volumes.

Volumetric pipette: It is made to deliver a well-defined volume (nominal volume),

which is given by one or two marks on the pipette.

Management of the pipette

1. The liquid is sucked by a vacuum using suction bulb light or propipette never

mouth.

2. Make sure there are no bubbles or foam in the liquid.

3. Clean the pipette tip before moving liquid.

4. Fill the pipette on the graduation mark and transfer the desired volume. The

edge of the meniscus should be on the graduation mark.

Margin of Error by Pipette Capacity.

Capacity (until) Error Limit

2 0,006

5 0,01

10 0,02

30 0,03

50 0,05

100 0,08

200 0,10

Graduated Cylinder

A graduated cylinder is a relatively slim glass or plastic cylinder used

specifically for calibrating beakers or measuring a liquid's volume. Graduated

cylinders come in a variety of sizes such as 10 ml, 25 ml, 50 ml, 100 ml, 500 ml

and 1,000 ml. Scientists take measurements by viewing, at eye-level, the lowest

point of the convex dip that the liquid in the cylinder makes.

Burettes

They are long graduated tubes, of uniform inner diameter throughout its length,

with a key chain or a clamp adapted of Mohr, so allowing pouring liquid dropwise.

Used to deliver variable amounts of liquid with great accuracy and precision, and

therefore, they have several subdivisions.

Utilization

1. When working with a burette, keep it upright , fixing on a stand.

2. Prior to the assessment itself, the buret must be rinsed with several small

portions of the solution with which it will be filled.

3. Fill the burette above the 0.00 mL mark.

4. Some burettes have special tanks for an easier filling, but if necessary it can

be filled with the help of a graduated pipette or by pouring the liquid through

a funnel from a jar.

5. Open the clamp shut allowing it to fill burette. Consider that there are no air

bubbles, eliminate them if any ( for that, cover with a finger the output of

peak , remove the clip and press on the gum to remove all bubbles , if

necessary , refill the burette again always above the 0.00 mL mark).

6. Dry out the peak of the burette.

7. Supporting the peak in the clean dry container wall used to rule out liquid,

open the clamp until the liquid level reaches 0.00 mL , ie , the base of the

meniscus must be tangent to the line that marks 0.00 mL. The eyes should

be at the height of the stroke.

8. During the assessment, must observe care when handling the burette key

or Mohr clamp that is used to close the peak . This will be handled with the

non-working hand so that the hand surrounds the burette, and fingers can

make the necessary pressure on the clamp to release the liquid. The skilled

hand is thus free to shake the titration flask.

Eye Dropper

It is a hollow tube at its bottom end a conical form and closed at the top by a

knob or rubber thimble, used for transferring small amounts of liquid by pouring

dropwise.

In laboratories are widely used to add reagents, indicators liquids or small

amounts of product. Their use is not recommended when accuracy is required in

the amount of discharged liquid. For those cases are most appropriate instruments

like pipette or burette.

Test Tube

A test tube is a relatively slim glass or plastic vessel with a rounded bottom.

They are designed to hold small quantities of chemicals and feature a flared lip to

make pouring easier. Test tubes can hold liquid or solid chemicals and can be

used to contain small chemical reactions. The slimness of the test tube reduces the

spread of any vapors that may be produced by the reaction. In the lab, test tubes

typically hold samples or provide a small vessel for reaction.

The Pizeta

It is a sealed cylindrical vessel with screw cap, which has a tubular extension

having an opening, able to deliver water or liquid contained in the squeeze bottle

which, in small amounts is found.

Usually, it is made of plastic and its main function in the laboratory is "wash",

that is the reason because receives the name of bottle washer or wash bottle too. It

uses distilled water to remove or reagents impregnated materials.

Test Tube Rack

Used to hold test tubes.

Petri Dish

Forms and Features

Round container made of glass or plastic, having different diameters, it is shoal,

with a cover in the same way that the plate, but a little larger in diameter as it can

be placed on top and close the container as a lid.

Uses

1. It is used to observe different types of biological and chemical samples which

are enclosed within the plate.

2. It is used for growing of bacteria and other related species.

3. It is also used for solid knead together with the balance.

Precautions

It should be used with caution, since it must avoid contact with biological

organisms, in case working with them. Use protective attachment before working

with biological organisms (Robe, Gloves, etc.)

Burners

A Bunsen burner provides concentrated and adjustable heat for experiments. A

tube connects the burner to the laboratory gas supply. When the Bunsen burner is

lit, the flame can be adjusted using the air hole. Closing the air hole produces an

easily visible, luminous flame is produced that is not good for heating. It should be

opened when the Bunsen burner is used to heat chemicals.

A Bunsen burner serves to provide a ready source of heat in the laboratory. A

typical Bunsen burner, according to Practical Chemistry, employs a tube in which a

gas (such as methane) mixes with air. Once that gas is lit, an air hole in the tube

allows the user to adjust the size of the flame.

Thiele tube

It is mainly used for the determination of melting points of a given substance. To

this is filled with a liquid having a high melting point, and heated. Its peculiar shape

causes convection currents formed by heating the entire tube to maintain constant

temperature.

Tongs

Tongs are used to grip certain materials and transfer hot items safely. They look

similar to scissors and are griped in the same way. The tongs can withstand a lot of

heat and so are very useful to use in most experiments.

Evaporating Dish

An evaporating dish is a glazed porcelain vessel used to heat and consequently

evaporate liquids. In this way experiments can increase a liquid's concentration.

The dish is relatively shallow and features a lip to facilitate pouring the liquids.

Mortar

Mortar aims crushing or grinding the solid substances.

Features and Forms

Mortar has a small instrument created from the same material called "Hand or

pylon" and is responsible for the shredding. They are usually found in wood,

porcelain, stone and marble.

Precautions

If the crush hazardous substances or liquids together with solid, they should be

milled or ground very gently to avoid splashing.

2. Weighing equipment.

Triple Beam Balance

Used to measure mass in grams.

Spatula

This tool is classified as metal materials residing in the lab. The spatula is a

narrow flat sheet which is attached to a handle made of wood, plastic or metal. It is

mainly used to take small quantities of compounds or solid substances, especially

granular.

3. Separation Equipment

Centrifuge

A centrifuge is a simple spinning device used to separate materials in a liquid

substance. Used often to separate blood and plasma samples, the centrifuge also

can separate different parts of petroleum or any liquid, and occasionally a solid

mixture.

Funnel

Aids in pouring liquids into small openings without spilling them.

Separatory Funnel

This instrument is mainly used for separating immiscible liquids or insoluble (not

mixed) that are separated by difference in density or molecular properties that they

possess.

By a certain time these diverge into two or more fractions depending upon the

amount of product into the container contents.

4. Support Equipment

Ring Stand

A stand used to support a ring clamp or test tube clamp.

Ring Clamp

Used to clamp onto a ring stand to sit a beaker or flask.

Bosshead

This tool is classified into metal material residing in the laboratory. The Purpose

having the bosshead is to hold other tools such as pliers or ring, which is subject to

the universal support.

5. Instruments with a Specific Use.

Multimeter

Any laboratory that deals with experiments involving electricity or electronics will

have a multimeter. Depending on the quality and type, multimeters can measure

voltage, current and resistance. Most multimeters provide the option for

measurements in alternating current (AC) or direct current (DC). Some may also

provide capacitance and inductance measurements. Equipment in any one

scientific laboratory will depend on the research and the relative skills of the

researchers. Whatever their sophistication and current field of scientific study, all

scientists will have used some common pieces of laboratory apparatus at some

point in their careers.

Microscopes

A compound microscope allows the user to view specimens too small for the

human eye to discern. Slides hold the specimen and often come prepared and

stained ahead of time. Slide preparation can also occur at the time of viewing.

Items commonly observed with compound microscopes include plant or animal

cells and bacteria.

Desiccator

It is made from very thick glass and in it two cavities are distinguished, the first

and largest upper cavity, can make dry the substance and one lower cavity is used

to put the desiccant, most commonly silica gel.

It also has a stopcock or valve on the side or on top, allowing the air extraction

to leave it vacuum. Being vacuum sealing lid is always difficult to reopen.

The dryer is made up by a strong glass and other times can be made in porcelain.

6. Other Instruments

Rubber Stoppers

Used to plug a flask or test tube for safe keeping.

Test Tube Brush

Used to clean test tubes.

Errors and Uncertainty in Experimental Data

Causes and Types of Errors

Conducting research in any science course is dependent upon obtaining

measurements. No measure is ever exact due to errors in instrumentation and

measuring skills. If you were to obtain the mass of an object with a digital balance,

the reading gives you a measure with a specific set of values. We can assume that

the actual measure lies either slightly above or slightly below that reading. The

range is the uncertainly of the measurement taken. More accurate instruments

have a smaller range of uncertainty. Whenever you take a measurement, the last

recorded digit is your estimate. We call digits in a measurement significant figures.

To better understand the outcome of experimental data an estimate of the size

of the systematic errors compared to the random errors should be considered.

Random errors are due to the accuracy of the equipment and systematic errors are

due to how well the equipment was used or how well the experiment was

controlled.

1. Random errors: Precision (Errors inherent in apparatus.)

A random error makes the measured value both smaller and larger than the

true value. Chance alone determines if it is smaller or larger. Reading the scales of

a balance, graduated cylinder, thermometer, etc. produces random errors. In other

words, you can weigh a dish on a balance and get a different answer each time

simply due to random errors. They cannot be avoided; they are part of the

measuring process. Uncertainties are measures of random errors. These are

errors incurred as a result of making measurements on imperfect tools which can

only have certain degree of accuracy. They are predictable, and the degree of error

can be calculated. Generally they can be estimated to be half of the smallest

division on a scale. For a digital reading such as an electronic balance the last digit

is rounded up or down by the instrument and so will also have a random error of ±

half the last digit.

2. Systematic errors: Accuracy (Errors due to "incorrect" use of equipment or poor

experimental design.)

A systematic error makes the measured value always smaller or larger than the

true value, but not both. An experiment may involve more than one systematic

error and these errors may nullify one another, but each alters the true value in one

way only. Accuracy (or validity) is a measure of the systematic error. If an

experiment is accurate or valid then the systematic error is very small. Accuracy is

a measure of how well an experiment measures what it was trying to measure.

These are difficult to evaluate unless you have an idea of the expected value (e.g.

a text book value or a calculated value from a data book). Compare the

experimental value to the literature value. If it is within the margin of error for the

random errors then it is most likely that the systematic errors are smaller than the

random errors. If it is larger then it’s needed to determine where the errors have

occurred.

Categories of Systematic Errors and how to eliminate them:

a. Personal errors: These errors are the result of ignorance, carelessness,

prejudices, or physical limitations on the experimenter. This type of error can be

greatly reduced if the person is familiar with the experiment you are doing. Be sure

to thoroughly read over every lab before use the equipment.

b. Instrumental Errors: Instrumental errors are attributed to imperfections in the

tools with which the analyst works. For example, volumetric equipment such as

burets, pipets, and volumetric flasks frequently deliver or contain volumes slightly

different from those indicated by their graduations. Calibration can eliminate this

type of error.

c. Method Errors: This type of error many times results when people do not

consider how to control an experiment. For any experiment, ideally the person

should have only one manipulated (independent) variable. Many times this is very

difficult to accomplish.

Bibliography

Elementary principles for laboratory instruments/Leslie W. Lee, L. M.

Schmidt/House: C.V. Mosby, year: 1983/ Pages: 379.

Laboratory instruments their design and application/A. Elliott & J/House:

Dickson Laboratory Instruments (2nd.ed.) year: 1959.

The Laboratory Companion: A Practical Guide to Materials, Equipment, and

Technique/Gary S. Coyne/ House: Wiley (1st. ed.) year: 1989.

Commonly Used Lab Equipment.

http://teachertech.rice.edu/Participants/louviere/vms/science/labequipment.

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Laboratory Equipment.

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