BIOL 207: Lab 2
BIOLOGY 207 LABORATORY 2
SOLUTIONS, DIFFUSION AND OSMOSIS
STUDENT LEARNING OBJECTIVES
1. Define various solutions in terms of solute and solvent.
2. Learn to calculate solution concentrations based on osmolality and percent solutions.
3. Understand solubility in the context of polar, nonpolar and ionic solutes and solvents, and understand
how solubility affects membrane transport and other aspects of physiology
4. Describe diffusion, osmosis, osmotic pressure and tonicity from the perspective of cells.
5. Examine cells exposed to various hypotonic, hypertonic and isotonic solutions. Understand the
changes in cells after exposure to these solutions and how this relates to basic human physiology.
GENERAL STATEMENT REGARDING SUBJECT MATTER
Solutions
The concepts of solute, solvent and solution are very important in physiology. To increase your familiarity with these
concepts, the first part of this laboratory deals with different ways of expressing concentrations of solutions and serial
dilutions. In this lab, you will be required to do fundamental calculations regarding concentrations. These calculations
will allow you to become familiar the concept of solutions and concentration. It is imperative that you understand the
various concepts in this section, as you will be expected to use them throughout the semester.
Diffusion, Osmosis, Tonicity
Solubility, diffusion, osmosis, and the property of tonicity are important in human physiology. For instance, you have
several hormones that contribute to maintaining a nearly constant osmotic condition in your bodily fluids. A rapid
change in the osmotic properties of your bodily fluids can be harmful, especially in very young and very old persons
since the homeostatic mechanisms required to maintain osmotic properties may be sluggish or not fully developed.
Numerous proteins embedded in the plasma membranes of your cells allow for the diffusion of ions and other
molecules down their concentration gradients, and your cells use these gradients to move materials into and out of
them. In contrast, the movement of nonpolar molecules and gases into and out of your cells relies on simple diffusion
which doesn’t involve proteins. Finally, tonicity is a concept that describes the movement of water into or out of cells
as dictated by osmotic pressure and solute concentration. We will explore the effect of isotonic, hypotonic and
hypertonic solutions on cells. Again, these concepts will be with you all semester so it is important that you become
familiar with them.
READING in HUMAN PHYSIOLOGY, 14th Edition, Stuart Ira Fox.
molarity and molality: pp. 138-139 osmolality and tonicity: pp. 139-141
diffusion, osmosis and osmotic pressure: pp. 133-138 chemical
bonds and hydrophobicity and hydrophilicity: pp. 26-29
selective permeability of membranes: p. 52-54, 132-133, much of chapter 6
LAB 2 CONVERSIONS & FORMULAS YOU MUST MEMORIZE & KNOW HOW TO USE FOR
LAB QUIZ 1 AND LAB EXAM 1:
For water, 1 kg = 1 L % solution = (grams solute/ml solvent) x 100
C1V1=C2V2
1000 ml = 1 L Osmolality = molality x # particles in water
10 dl = 1 L Milliosmolality = osmolality x 1000
Ask you lab instructor if they will require that you memorize any additional conversions, values or formulas.
2.1
, BIOL 207: Lab 2
Ex. 2.1: Solutions and Calculating Concentrations (background for calculations on p. 2.10)
A solution is a homogenous mixture of two or more substances. The substance present in the greatest
amount is called the solvent, while the substances present in the smaller amounts are called the solutes.
Another way of describing the relationship of solute and solutes is that solutes are the molecules that are
dissolved in the solvent. For instance, in a salt water solution, the salt is the solute and the solvent is the
water. In physiology, the solutions that we deal with are usually liquid solutions, in which water is the
solvent, and the solutes can be a variety of molecules such as salts (e.g. NaCl), sugars (e.g. glucose),
proteins, and gases. Our bodies are full of solutions. Our cells are filled with a solution known as the
cytoplasm. In the blood, our cells are bathed in a solution known as the plasma, and in our tissues are cells
are surrounded by a solution known as the interstitial fluid.
Concentration of solutions:
The concentration of a solution relates the amount of solute to the amount of solvent in a solution
(concentration = solute/solvent). In physiology you will frequently encounter concentrations. For instance,
fasting blood glucose levels must be maintained at 75-100 mg/dl, normal saline solutions found in IV fluids
are at 0.9% NaCl, pH is related to the molar hydrogen ion concentration in a solution, and blood plasma has
a set point of around 300 mOsm. In the tonicity activity today we’ll see that the concentration of solutes
inside and outside the cell is critical to cell shape, function and survival.
Concentration always relates the amount of solute to solvent in a solution, but the amounts can be expressed
as mass, volumes, or even in terms of the number of atoms, molecules or particles. Mass is the amount of
matter. Kilograms (kg), grams (g) and milligrams (mg) are all examples of units of mass. Volume is the
amount of space that matter takes up. Liters (L), deciliters (dl), and milliliters (ml) are all examples of units
of measurements of volume. Following are some common ways that concentration can be expressed:
a) Weight per volume
e.g. mg/dl and mg/100 ml are common weight per volume units used in physiology
b) Percentage (% ) solutions
Percentage solutions are a subtype of a weight per volume concentration. Percentage means
"parts in 100." For example, percentage is the number of grams of solute dissolved in 100 ml (or
a dl)* of solution. It can be expressed as follows:
percentage = (grams solute/volume of solvent in milliliters) X 100
EXAMPLE 1: a 9% solution of sodium chloride (NaCl):
9% NaCl = (9 grams of NaCl/ 100 ml of solution) X 100
EXAMPLE 2: a 0.09% solution of glucose is the average human blood concentration of glucose.
0.09% = (90 mg of glucose/ 100 ml of blood) X 100
Note: 90 mg (milligrams) is the same as 0.090 grams. A milligram is 1/1000 of a gram so to get
milligrams, you multiply the number of grams by 1000. Thus, 0.09 grams in milligrams is 0.09 X
1000 or 90 milligrams (mg).
2.2
, BIOL 207: Lab 2
c) Molarity (M) and molality (m)
The equations for molarity and molality are as follows.
1) Molarity (M) = moles of solute/L of solution
2) Molality (m) = moles solute/ kg of solvent
As you can see, both molar (M) and molal (m) solutions express the amount of solute in
terms of moles. A mole is just a specific number of atoms or molecules. One mole of any
substance contains 6.02 x 1023 molecules. Therefore, solutions of equal molality or of equal molarity
have the same number of molecules in solution even through the molecules may be different (have
different molecular weights). For example: Approximately 1 kg of a 1 m sucrose and 1 m urea both
have 6.02 x 1023 molecules. Likewise, approximately 1 kg of 0.5 m NaCl and 0.5 m C6H12O6 both
have (6.02 x ) molecules. The weight in grams of one mole of a substance equals the
molecular weight (or atomic weight or molar mass) of that substance. Atomic weights (molar mass)
for the elements are given in the Periodic Table of the Elements. Molecular weights are computed by
adding the individual atomic weights of the atoms that make up a molecule.
The difference between a molar (M) and molal (m) solution is in the preparation of the
solutions. For instance if you were preparing 1 L of a 1 M sucrose solution, you add 1 mole of
sucrose to the container, and then add just enough water to make the final solution volume 1 L.
Thus, you would have exactly 1 L of the 1 M sucrose solution. However, if you were preparing
approximately 1 kg of a 1 m sucrose solution, you would add 1 mole of sucrose to the container and
then add exactly 1 kg (= 1 L) of water , and since the sucrose takes up a little bit of space, the total
solution volume would be a little more than 1 L of solution.
If you take a chemistry class, you will need to know how to calculate molarity and molality, but
for this class you will not need to perform these calculations.
d) Osmolality (Osm)
Osmolality is related to molality, but while molality considers the moles per kg of solute,
osmolality also takes into account the number of particles that a molecule would become if
dissolved in water. Molecules held together by ionic bonds dissociate when placed in water as
water forms spheres of hydration around the ions. Thus, a molecule such as NaCl, which is
held together by ionic bonds will dissociate into separate Na+ and Cl- ions in water. However,
molecules held together by covalent bonds stay intact when dissolved in water. For instance, if
you dissolve the sugar sucrose (C12H22O11) in water, the sucrose molecules will not break apart
into separate C, H and O atoms, but instead will remain as C12H22O11 molecules. Osmolality
(Osm) = molality x # of particles in water
Milliosmolality (mOsm) = osmolality x 1000
EXAMPLE 1: What is the osmolality of 0.1 m sucrose solution, assuming that sucrose is held
together by covalent bonds?
0.1 m x 1 particle = 0.1 Osm
EXAMPLE 2: What is the osmolality of a 0.1 m NaCl solution, assuming that NaCl is held
together by ionic bonds?
0.1 x 2 particles = 0.2 Osm
2.3
BIOLOGY 207 LABORATORY 2
SOLUTIONS, DIFFUSION AND OSMOSIS
STUDENT LEARNING OBJECTIVES
1. Define various solutions in terms of solute and solvent.
2. Learn to calculate solution concentrations based on osmolality and percent solutions.
3. Understand solubility in the context of polar, nonpolar and ionic solutes and solvents, and understand
how solubility affects membrane transport and other aspects of physiology
4. Describe diffusion, osmosis, osmotic pressure and tonicity from the perspective of cells.
5. Examine cells exposed to various hypotonic, hypertonic and isotonic solutions. Understand the
changes in cells after exposure to these solutions and how this relates to basic human physiology.
GENERAL STATEMENT REGARDING SUBJECT MATTER
Solutions
The concepts of solute, solvent and solution are very important in physiology. To increase your familiarity with these
concepts, the first part of this laboratory deals with different ways of expressing concentrations of solutions and serial
dilutions. In this lab, you will be required to do fundamental calculations regarding concentrations. These calculations
will allow you to become familiar the concept of solutions and concentration. It is imperative that you understand the
various concepts in this section, as you will be expected to use them throughout the semester.
Diffusion, Osmosis, Tonicity
Solubility, diffusion, osmosis, and the property of tonicity are important in human physiology. For instance, you have
several hormones that contribute to maintaining a nearly constant osmotic condition in your bodily fluids. A rapid
change in the osmotic properties of your bodily fluids can be harmful, especially in very young and very old persons
since the homeostatic mechanisms required to maintain osmotic properties may be sluggish or not fully developed.
Numerous proteins embedded in the plasma membranes of your cells allow for the diffusion of ions and other
molecules down their concentration gradients, and your cells use these gradients to move materials into and out of
them. In contrast, the movement of nonpolar molecules and gases into and out of your cells relies on simple diffusion
which doesn’t involve proteins. Finally, tonicity is a concept that describes the movement of water into or out of cells
as dictated by osmotic pressure and solute concentration. We will explore the effect of isotonic, hypotonic and
hypertonic solutions on cells. Again, these concepts will be with you all semester so it is important that you become
familiar with them.
READING in HUMAN PHYSIOLOGY, 14th Edition, Stuart Ira Fox.
molarity and molality: pp. 138-139 osmolality and tonicity: pp. 139-141
diffusion, osmosis and osmotic pressure: pp. 133-138 chemical
bonds and hydrophobicity and hydrophilicity: pp. 26-29
selective permeability of membranes: p. 52-54, 132-133, much of chapter 6
LAB 2 CONVERSIONS & FORMULAS YOU MUST MEMORIZE & KNOW HOW TO USE FOR
LAB QUIZ 1 AND LAB EXAM 1:
For water, 1 kg = 1 L % solution = (grams solute/ml solvent) x 100
C1V1=C2V2
1000 ml = 1 L Osmolality = molality x # particles in water
10 dl = 1 L Milliosmolality = osmolality x 1000
Ask you lab instructor if they will require that you memorize any additional conversions, values or formulas.
2.1
, BIOL 207: Lab 2
Ex. 2.1: Solutions and Calculating Concentrations (background for calculations on p. 2.10)
A solution is a homogenous mixture of two or more substances. The substance present in the greatest
amount is called the solvent, while the substances present in the smaller amounts are called the solutes.
Another way of describing the relationship of solute and solutes is that solutes are the molecules that are
dissolved in the solvent. For instance, in a salt water solution, the salt is the solute and the solvent is the
water. In physiology, the solutions that we deal with are usually liquid solutions, in which water is the
solvent, and the solutes can be a variety of molecules such as salts (e.g. NaCl), sugars (e.g. glucose),
proteins, and gases. Our bodies are full of solutions. Our cells are filled with a solution known as the
cytoplasm. In the blood, our cells are bathed in a solution known as the plasma, and in our tissues are cells
are surrounded by a solution known as the interstitial fluid.
Concentration of solutions:
The concentration of a solution relates the amount of solute to the amount of solvent in a solution
(concentration = solute/solvent). In physiology you will frequently encounter concentrations. For instance,
fasting blood glucose levels must be maintained at 75-100 mg/dl, normal saline solutions found in IV fluids
are at 0.9% NaCl, pH is related to the molar hydrogen ion concentration in a solution, and blood plasma has
a set point of around 300 mOsm. In the tonicity activity today we’ll see that the concentration of solutes
inside and outside the cell is critical to cell shape, function and survival.
Concentration always relates the amount of solute to solvent in a solution, but the amounts can be expressed
as mass, volumes, or even in terms of the number of atoms, molecules or particles. Mass is the amount of
matter. Kilograms (kg), grams (g) and milligrams (mg) are all examples of units of mass. Volume is the
amount of space that matter takes up. Liters (L), deciliters (dl), and milliliters (ml) are all examples of units
of measurements of volume. Following are some common ways that concentration can be expressed:
a) Weight per volume
e.g. mg/dl and mg/100 ml are common weight per volume units used in physiology
b) Percentage (% ) solutions
Percentage solutions are a subtype of a weight per volume concentration. Percentage means
"parts in 100." For example, percentage is the number of grams of solute dissolved in 100 ml (or
a dl)* of solution. It can be expressed as follows:
percentage = (grams solute/volume of solvent in milliliters) X 100
EXAMPLE 1: a 9% solution of sodium chloride (NaCl):
9% NaCl = (9 grams of NaCl/ 100 ml of solution) X 100
EXAMPLE 2: a 0.09% solution of glucose is the average human blood concentration of glucose.
0.09% = (90 mg of glucose/ 100 ml of blood) X 100
Note: 90 mg (milligrams) is the same as 0.090 grams. A milligram is 1/1000 of a gram so to get
milligrams, you multiply the number of grams by 1000. Thus, 0.09 grams in milligrams is 0.09 X
1000 or 90 milligrams (mg).
2.2
, BIOL 207: Lab 2
c) Molarity (M) and molality (m)
The equations for molarity and molality are as follows.
1) Molarity (M) = moles of solute/L of solution
2) Molality (m) = moles solute/ kg of solvent
As you can see, both molar (M) and molal (m) solutions express the amount of solute in
terms of moles. A mole is just a specific number of atoms or molecules. One mole of any
substance contains 6.02 x 1023 molecules. Therefore, solutions of equal molality or of equal molarity
have the same number of molecules in solution even through the molecules may be different (have
different molecular weights). For example: Approximately 1 kg of a 1 m sucrose and 1 m urea both
have 6.02 x 1023 molecules. Likewise, approximately 1 kg of 0.5 m NaCl and 0.5 m C6H12O6 both
have (6.02 x ) molecules. The weight in grams of one mole of a substance equals the
molecular weight (or atomic weight or molar mass) of that substance. Atomic weights (molar mass)
for the elements are given in the Periodic Table of the Elements. Molecular weights are computed by
adding the individual atomic weights of the atoms that make up a molecule.
The difference between a molar (M) and molal (m) solution is in the preparation of the
solutions. For instance if you were preparing 1 L of a 1 M sucrose solution, you add 1 mole of
sucrose to the container, and then add just enough water to make the final solution volume 1 L.
Thus, you would have exactly 1 L of the 1 M sucrose solution. However, if you were preparing
approximately 1 kg of a 1 m sucrose solution, you would add 1 mole of sucrose to the container and
then add exactly 1 kg (= 1 L) of water , and since the sucrose takes up a little bit of space, the total
solution volume would be a little more than 1 L of solution.
If you take a chemistry class, you will need to know how to calculate molarity and molality, but
for this class you will not need to perform these calculations.
d) Osmolality (Osm)
Osmolality is related to molality, but while molality considers the moles per kg of solute,
osmolality also takes into account the number of particles that a molecule would become if
dissolved in water. Molecules held together by ionic bonds dissociate when placed in water as
water forms spheres of hydration around the ions. Thus, a molecule such as NaCl, which is
held together by ionic bonds will dissociate into separate Na+ and Cl- ions in water. However,
molecules held together by covalent bonds stay intact when dissolved in water. For instance, if
you dissolve the sugar sucrose (C12H22O11) in water, the sucrose molecules will not break apart
into separate C, H and O atoms, but instead will remain as C12H22O11 molecules. Osmolality
(Osm) = molality x # of particles in water
Milliosmolality (mOsm) = osmolality x 1000
EXAMPLE 1: What is the osmolality of 0.1 m sucrose solution, assuming that sucrose is held
together by covalent bonds?
0.1 m x 1 particle = 0.1 Osm
EXAMPLE 2: What is the osmolality of a 0.1 m NaCl solution, assuming that NaCl is held
together by ionic bonds?
0.1 x 2 particles = 0.2 Osm
2.3
