EXERCISE 4: pH, ACIDS, BASES, AND BUFFERS
Lab 2_DL
Week#2
• MICROSCOPE
• pH, ACIDS, BASES, AND BUFFERS
TODAY
The compound
microscope
The compound microscope
OCULAR LENS (eyepiece) – Your microscope have two (binocular) ocular
lenses. These are the lenses you will look through when examining a
specimen with the microscope. Each ocular lens magnifies the image by a
factor of 10 or 10X.
OBJECTIVE LENSES – The set of objective lenses are on the revolving
nosepiece. These lenses allow you to change the degree of magnification.
Our microscopes have four objective lenses. The degree of magnification
for each objective lens is indicated on its side.
5X – This objective magnifies the image by a factor of 5. It is refe
ed to as the
“scanning objective” since it is used to scan the slide to locate the specimen before
viewing it at higher magnification.
10X – This objective magnifies the image by a factor of 10 and is refe
ed to as the
“low power” objective.
40X – This objective magnifies the image by a factor of 40 and is refe
ed to as the
“high power” objective.
100X – This objective magnifies the image by a factor of 100. It is refe
ed to as the “oil
immersion objective” since it requires a drop of immersion oil on the slide to provide
good resolution.
Lenses of the compound microscope
The total magnification of an image is the product of the ocular lens
magnification times the magnification of the objective lens you are
using.
Magnification of ocular x magnification of objective = total magnification
For example, if the ocular lens magnifies the image by a factor of 10
(10X), and the objective lens magnifies the image by a factor of 40
(40X), the total magnification of the image is 400X. (10X x 40X = 400X)
Total Magnification
Field of View
The Field of View decreases when the magnification increases
The field of view (FOV) is the actual “circle” you see when looking in the microscope.
Although this circular field of view appears to be the same no matter which objective lens
you are using, this is not the case. The circular area you are actually viewing will decrease
as you increase the magnification.
The field of view
Objectives
• Once you have a specimen in focus under the microscope, if you
adjust the fine focus knob up and down the specimen will come in
and out of focus. Thus, there is a range in the vertical dimension in
which the specimen on your slide will appear in focus.
• The “thickness” of the vertical range in which the specimen remains
in focus is refe
ed to as the depth of focus.
• The depth of focus decreases as the magnification increases
Depth of focus
depth of focus
Depth of focus
Video of depth of focus https:
youtu.be/kJZh9wY37UM
Low magnification high magnification
The depth of focus decreases as the magnification increases
https:
youtu.be/kJZh9wY37UM
https:
youtu.be/kJZh9wY37UM
1. Place a drop of Water on the clean Slide
2. Place Specimen in a drop of water
3. Place one edge of cover glass against the slide so that cover
glass touches the water drop
4. Lower cover glass gently onto the slide.
Preparation of a wet-mount slide
Acids, Bases and pH (Ex 4)
An acid is a substance that increases the concentration of hydrogen ion (H+)
HCl à H+ + Cl-
A base is a substance that decreases the concentration of hydrogen ion (H+)
Hydrochloric acid
(hydrogen chloride)
Hydrogen
ion
chlorine
NH XXXXXXXXXXH+ à NH4+
Ammonia Hydrogen
ion
Ammonium ion (cation)
NaOH à Na XXXXXXXXXXOH-
OH XXXXXXXXXXH+ à H2O
Sodium
hydroxide
Sodium Hydroxide ion
Hydrogen
ion
wate
pH scale indicate the strength
of acids and bases
• The pH is a measure of the
hydrogen ion concentration in a
solution
o pH = -log [H+]
o [H+] = 10 -pH
• pH scale ranges from 0 to 14
• Acids have a pH less than 7
• Bases have a pH greater than 7
• Pure water has a pH of 7
Lab manual p41
Activity I: Determining pH of Different Solutions
2
4
13
11
6
3
4
6
5
3
2
11
acidic
acidic
asic
asic
acidic
acidic
acidic
acidic
acidic
acidic
acidic
asic
David
• A Buffer is a compound or a combination of compounds that can
combine with or release hydrogen ions to keep the pH of a
solution relatively constant.
• A buffer solution resists changes in pH when small quantities of
an acid or an alkali are added to it
Buffe
CH3COOH(aq) CH3COOH- + H+
Ethanoic acid Hydrogen
ion
Ethanoate
CH3COOH(aq) CH3COOH- + H+If acid added
CH3COOH(aq) + OH- CH3COOH- + H2OIf base added
• Organisms control the pH of cellular and body fluids
y using buffers.
e.g. Blood as a pH of 7.4 and serves also has a
uffe
Buffe
Lab manual p41
Activity II: The Action of a Buffe
water buffe
water buffe
Place 50 ml
of pure wate
Place 50 ml
of buffe
water buffe
Place 50 ml
of pure wate
Place 50 ml
of buffe
Measure the pH of
each beake
Add 1 mL of 0.1N HCl
then measure the pH
of each beaker.
Repeat 4 times
Lab manual p42
Activity II: The Action of a Buffe
7
7
6.5
7
6.5
7
7
6
5.5
4
3.5
3