Working in a Lab

Lab Safety 021

Glassware & Microscopes 046Measurements 053

Some Rules for Working in the Lab

Glassware Safety Glassware is vital to doing good science. If not handled with care, glassware can cause serious harm. Notify your teacher if you break glassware. Dispose of broken glass in the appropriate container. Remember that to use such equipment is a privilege.

Sharp Instrument SafetySharp instruments are needed in the lab. You must never use or pretend to use it on yourself or someone else. Remember that to use such equipment is a privilege.

Eye Safety Often labs require that you wear safety glasses. The purpose of such glasses is to prevent damage to your vision. If something should get into your eyes, make sure you let your teacher know. The glasses shown here are for impact safety. Safety goggles that are vented should be used when working with chemicals. Alcohol wipes should be used to clean the goggles before using. Remember that to use such equipment is a privilege.

Electrical Safety Many labs involve the use of electrical devices. When you plug in such electrical equipment, make sure you include the ground plug (round). Hold the plug firmly by the insulating cover when plugging it in or unplugging it. NEVER unplug an electrical device by pulling on its cord! Remember that to use such equipment is a privilege.

Chemical Safety Often labs involve the use of chemicals. Please be careful to keep chemicals off your skin and out of your mouth and eyes. If you get any chemical on your skin or in your eyes, INFORM your teacher immediately! Remember that to use such chemicals is a privilege.

Microscope parts

Using a microscope

• Your microscope has 3 magnifications: Scanning, Low and High. Each objective will have written the magnification. In addition to this, the ocular lens (eyepiece) has a magnification.

• The total magnification is the

ocular x objective

When you look through the eyepiece, the lighted area you see is the

FIELD OF VIEW.

MagnificationThe eyepiece lens has a magnifying power of 10x. The objective lens being used has a magnifying power of 4x. To find the total magnification, multiply these two numbers:

Measurement

• A measurement is a repeatable observation of quantity that includes a number and a unit. An estimate is a reasonable guess at a quantity based on an observation.

The water took a long time to boil.

The water took exactly 18 minutes

to boil.

The water took almost a quarter hour to boil.

SI system

• SI system of measurement stands for “Systeme International” which is French for International System. It is also called the Metric System.

Base UnitsQuantity Unit used in SI (symbol)

Length or distance Meter (m)

Volume or capacity Liter (L)

Mass Gram (g)

Density Gram per cubic centimeter (g/cm3)

Time Second (s)

Temperature Degrees Celsius (C)

Measuring Liquid Volume1. Pour liquid into a graduated

cylinder.2. Move your head so the top of the

liquid in the cylinder is at eye level.

3. Look for the meniscus, the curved surface of the liquid. You may find it easier to see the meniscus if you hold a sheet of white paper behind the graduated cylinder.

4. A water meniscus is about as thick as a nickel. Read the volume at the bottom of the meniscus. If the volume is between two marks on the cylinder, estimate the volume.

Volume of Rectangular Solids

• The cubic centimeter (cm3 or cc) is a common unit of volume. It is usually used to measure the volume or capacity of a rectangular solid, or box. The volume of a box equals its length times its width times its height.

Volume = length x width x height

V = L x W x H

Triple-beam balance

Mass

Rear weight is in the notch reading...... 70 g

Middle weight is in the notch............... 300 g

Front beam weight reads....................3.34 g

The object weighs............. 373.34 g

Density

1. Know the simple mathematical formula for calculating the density of a substance. To use this formula, you will have to know the mass and the volume of the substance. The mass refers to the gravitational pull on the substance and how much matter it contains. The volume refers to the amount of three-dimensional space the substance occupies.

Step 2

• Calculate the volume of the substance by measuring the length, width and height. The formula looks like this: Volume = L (length) x W (width) x H (height).

Step 3

If the object or substance is irregularly shaped, determine the volume by finding out how much water is displaced when the object is dropped into a beaker of water.

Next…

Calculate the density once you know the volume and mass of the substance or object. Density is equal to the mass of the substance divided by its volume: D (density) = M (mass) / V (volume).

Will it float?• Know that a substance or object with a higher

density has a higher measure of mass per unit of volume. A substance with a density that is greater than 1 g/cm cubed will sink in water because it is denser. A substance with a density below 1g/cm cubed will float because it is less dense than water whose density is approximately 1 g/cm cubed.