General Organic and Biological Chemistry An Integrated Approach

General, Organic, and Biological Chemistry: An Integrated Approach Laura Frost, Todd Deal and Karen Timberlake by Richard Triplett Chapter 7 Solution Chemistry: How Sweet Is Your Tea? © 2011 Pearson Education, Inc.

Monday 7. 1 Solutions Are Mixtures 7. 2 Formation of Solutions 7. 3 Chemical Equations for Solution Formation Wednesday 7. 4 Concentrations 7. 5 Dilution 7. 6 Osmosis and Diffusion Friday 7. 7 Transport Across Cell Membranes Chapter 7 2

Today’s Objectives q q Review formation of solutions Write equations for solutions © 2011

7. 1 Solutions Are Mixtures • A homogeneous mixture, such as a glass of tea, is called a solution. • Solutions consists of at least one substance, called a solute, evenly dispersed throughout a second substance, called the solvent. • Components of a solution do not react with one another. © 2011 Pearson Education, Inc. Chapter 7 4

• Solute is the substance present in the smallest amount. • Solvent is the substance present in the greatest amount. • When sugar is added to a glass of iced tea, sugar is the solute and water is the solvent. • Sugar, once dissolved in a glass of iced tea, will not come out of solution over time. © 2011 Pearson Education, Inc. Chapter 7 5

Properties of solutions are as follows: © 2011 Pearson Education, Inc. Chapter 7 6

Examples of Solutions Chapter 7 7

Phases of Solutes and Solvents • In addition to a solution made by adding a solid to a liquid, a gas can be a solution also. • For example, the air we breath is a solution in which nitrogen is the solvent and oxygen and other gases are the solute. • Metals, like brass, can be a solution of solids in solids. © 2011 Pearson Education, Inc. Chapter 7 8

• Brass is an alloy of the solute zinc in the solvent copper. • The solute and solvent can either be a solid, liquid, or gas in a solution. • Aqueous solutions are solutions in which water is the solvent. Chapter 7 9

Colloids and Suspensions • Some solutions appear to be solutions, but are not because they are not a transparent liquid. • Colloids are solutions of undissolved particles that do not separate over time. Milk is a colloid (or colloidal mixture) because it contains proteins and fats that do not dissolve. • Particles in a colloid must be between 1 and 1000 nanometers in diameter. Chapter 7 10

• Particles greater than 1000 nanometers in diameter will separate from a mixture when standing. These mixtures are considered suspensions. • Mud in water is considered a suspension. The larger particles will quickly settle with gravity. • Blood is considered a suspension. Blood cells will settle in a tube upon standing because they are greater than 1 micrometer in diameter. • Blood cells can be separated by centrifugation, a spinning process that accelerates settling. Chapter 7 11

© 2011 Pearson Education, Inc. Chapter 7 12

7. 2 Formation of Solutions • Recall the golden rule of solubility, like dissolves like, which explains why some compounds dissolve in water and others do not. • The dissolving process requires that individual solvent particles surround the solute molecules and interact through intermolecular forces or ion–dipole attractions. • Dissolving is a physical process, not a chemical process because the particles are just redistributing themselves. • The process of dissolving is referred to as solvation for all solutions, and more specifically, as hydration in the case of an aqueous solution. © 2011 Pearson Education, Inc. Chapter 7 13

Factors Affecting Solubility and Saturated Solutions • The maximum amount of a solute that can dissolve in a specified amount of solvent defines the solubility. Solubility depends on the polarity of the solute and solvent, and the temperature of the solvent. © 2011 Pearson Education, Inc. Chapter 7 14

• An unsaturated solution does not contain the maximum amount of solute in a given amount of solvent. • A saturated solution contains all the solute that can dissolve in a given amount of solvent. • If more solute is added to a saturated solution, the additional solute will remain undissolved. This solution reaches an equilibrium state between the dissolved and undissolved solute. © 2011 Pearson Education, Inc. Chapter 7 15

• At equilibrium, the rate of dissolving solute is the same as the rate of dissolved solute reforming crystals. • The equilibrium rates can be represented by the following chemical equation: © 2011 Pearson Education, Inc. Chapter 7 16

© 2011 Pearson Education, Inc. Chapter 7 17

• There are conditions in our body that result in the build up of undissolved solids in bodily fluids. • Gout occurs when uric acid crystals form in soft tissues, or in cartilage and tendons. Kidney stones form when compounds like calcium phosphate or calcium oxalate build up in the urinary tract, kidneys, urethra, or bladder. (See next slide illustration of gout. ) © 2011 Pearson Education, Inc. Chapter 7 18

Gout and Kidney Stones © 2011 Pearson Education, Inc. Chapter 7 19

Solubility and Temperature • Most solids dissolve in water when the temperature increases. • Solubility can manipulated by changing the temperature of a solution. • As temperature increases in a solution containing a gas, solubility of the gas decreases. © 2011 Pearson Education, Inc. Chapter 7 20

• For example, if an unopened soda can is left in a car on a hot day, the container can explode due to the release of carbon dioxide in solution as a result of the elevated temperature. • Solubility of a gas in a solution is related to pressure and temperature. • Solubility of a gas dissolved in water decreases with a rise in temperature. © 2011 Pearson Education, Inc. Chapter 7 21

Solubility and Pressure—Henry’s Law • Pressure affects the solubility of a gas in a liquid. • Henry’s law states that the solubility of a gas in a liquid is directly related to the pressure of the gas over the liquid. That is, the amount of gas that can dissolve in a liquid increases as the pressure of the gas in the space above the liquid increases. © 2011 Pearson Education, Inc. Chapter 7 22

• An example of Henry’s law is demonstrated when a can of soda is opened at room temperature and poured into a glass. The dissolved carbon dioxide will fizz and escape from the liquid. • The hissing sound made when a soda is opened is a result of the space above the beverage in the container, which is filled with carbon dioxide at a higher pressure than the surrounding atmosphere. The gas then escapes quickly once the seal is broken. © 2011 Pearson Education, Inc. Chapter 7 23

The amount of carbon dioxide that was dissolved in the drink at a higher

• Another example of Henry’s law can be seen when studying how the lungs remove carbon dioxide from blood, but add oxygen. • The pressure of carbon dioxide is higher in the blood delivered back to the lungs than the pressure of carbon dioxide in the lungs. Therefore, this gas will pass out of the bloodstream into the lungs where it can be expired. © 2011 Pearson Education, Inc. Chapter 7 25

Oxygen dissolves into the blood at the lungs because the pressure of oxygen in

7. 3 Chemical Equations for Solution Formation • Pure water does not conduct electricity, but tap water will. Why is this? • Tap water contains dissolved ions, and these ions conduct electricity. • Solutes that produce ions in solution are called electrolytes. • Ionic compounds, like Na. Cl, that completely dissociate when they dissolve in water are considered strong electrolytes. © 2011 Pearson Education, Inc. Chapter 7 27

• Covalent compounds, like sugar, do not ionize in solution when they dissolve, so no ions are formed. Instead they exist as molecules. • Soluble covalent compounds do not conduct electricity and are referred to as nonelectrolytes. • Some covalent compounds will partially ionize in water. These compounds are termed weak electrolytes and are weak conductors of electricity. © 2011 Pearson Education, Inc. Chapter 7 28

© 2011 Pearson Education, Inc. Chapter 7 29

• In a chemical equation, the reactants always appear on the left side, and the products always appear on the right side. They are separated by an arrow which means react to form or yield. • A general chemical equation is shown as: © 2011 Pearson Education, Inc. Chapter 7 30

Strong Electrolytes • An ionic compound like magnesium chloride will yield magnesium ions and chloride ions when dissolved in water. This is shown in a chemical equation as: • Note that the number of magnesium and chloride ions formed in the products is the same as the number of each found in the reactant. © 2011 Pearson Education, Inc. Chapter 7 31

• The number of ions in the product is the same as the number of each found in the reactant. • The law of conservation of mass states that matter is neither created nor destroyed. Matter merely changes form. Atoms cannot appear or disappear. • After writing a reaction, it is important to inspect it to make sure that the number of each element is the same on the product and reactant side of the equation. © 2011 Pearson Education, Inc. Chapter 7 32

• When the number of elements are the same on the reactant and product side of the equation, we say the equation is balanced. • Subscripts that appear in formulas for compounds and the full-size numbers in front of particles indicate the total number of a particle present. These full-size numbers are referred to as coefficients. • Balancing requires that the charge be the same on both sides of the chemical equation. © 2011 Pearson Education, Inc. Chapter 7 33

• In the above equation, the 2 in front of the chloride ion indicates that there are two chloride ions produced for every one Mg. Cl 2 that dissociates. • The Mg. Cl 2 has no net charge, and one Mg 2+ and two Cl- sum to a total charge of zero, so the charges are balanced. © 2011 Pearson Education, Inc. Chapter 7 34

• Note that the arrow points in one direction, implying that the process is irreversible. • The phases of matter are indicated. The reactants will usually be a solid that dissolves, and the products will be aqueous. • The H 2 O appearing below the arrow indicates this process occurs in water. © 2011 Pearson Education, Inc. Chapter 7 35

Nonelectrolytes • Nonelectrolytes are polar compounds that dissolve in water, but do not ionize in water. • Covalent compounds like glucose do not dissociate. • The phase of the product is changed to aqueous in this type of representation. © 2011 Pearson Education, Inc. Chapter 7 36

Weak Electrolytes • The organic functional group that partially ionizes in solution is the carboxylic acid. • This functional group has an ionic form known as the carboxylate group. • Carboxylic acids are weak electrolytes. © 2011 Pearson Education, Inc. Chapter 7 37

• Partial ionization of acetic acid is shown as: • The carboxylic acid group contains a very polar O–H bond that can dissociate to form the carboxylate ions and H+ ions when dissolved. • The rates of the forward and reverse reactions equalize until the amount of acetic acid and the ions no longer changes. © 2011 Pearson Education, Inc. Chapter 7 38

• In the equation of the dissociation of acetic acid, the number of atoms and the total charge on each side is balanced. • The phase of the weak electrolyte before hydration may be liquid, gas, or solid. • The steps for writing and balancing equations for both ionic and covalent compounds are shown on the next slide. © 2011 Pearson Education, Inc. Chapter 7 39

© 2011 Pearson Education, Inc. Chapter 7 40

Ionic Solutions and Equivalents • Blood and other bodily fluids contain many different electrolytes, like Na+, K+, Cl-, and HCO 3 -, as dissolved ions. • The amount of dissolved ion can be expressed by the equivalent (Eq). • An equivalent relates the charge in a solution to the number of ions or moles of ions present. © 2011 Pearson Education, Inc. Chapter 7 41

The number of equivalents present per mole of an ion equals the charge of

Today’s Objectives ü ü Review formation of solutions Write equations for solutions © 2011

Objectives for Today q q Calculate concentration in different units Dilution Equation Osmosis and Diffusion Cell membranes (possible) Chapter 7 44

7. 4 Concentrations • The concentration of a solution can be expressed in different units. • Concentration is defined as the amount of solute dissolved in a given amount of solution. • The denominator is the total amount of solution, which includes the amount of solute. © 2011 Pearson Education, Inc. Chapter 7 45

The units of concentration vary depending on the type of solute. This table shows the normal concentration ranges of some substances tested in blood along with readable units. © 2011 Pearson Education, Inc. Chapter 7 46

Milliequivalents per Liter (m. Eq/L) • Electrolytes in bodily fluids are represented by the concentration unit of milliequivalents per liter of solution. 1000 m. Eq = 1 Eq • Ionic solutions have a balance in the number of positive and negative charges present because the dissolving ionic compounds have no net charge. © 2011 Pearson Education, Inc. Chapter 7 47

Blood plasma has a total electrolyte concentration of 150 m. Eq/L, meaning that the

Concentrations of other ionic solutions used as intravenous fluids are shown in this table.

Millimoles per Liter (mmol/L) and Molarity (M) • Units of electrolytes are sometimes given in mmoles/L instead of m. Eq/L. • The charge on an ion is the number of equivalents present in 1 mole. • An ion like Na+ has a 1+ charge, so the number of equivalents is equal to the number of moles, and the units mmole/L and m. Eq/l are identical. © 2011 Pearson Education, Inc. Chapter 7 50

• We can show this equivalency mathematically by converting m. Eq/L to mmole/L using the following conversion factor: • Using this conversion factor, we can determine the concentration of a 135 m. Eq/L Na+ solution in mmole/L. © 2011 Pearson Education, Inc. Chapter 7 51

• A unit related to mmole/L is used in the laboratory to describe the concentrations of solutions. This unit is molarity, M, which is the number of moles of solute in 1 L of solution. • The mole is related to the number of molecules present by Avogadro’s number. © 2011 Pearson Education, Inc. Chapter 7 52

• For example, a 3. 0 M solution of substance A will have the same number of molecules as a 3. 0 M solution of substance B, even though the masses of A and B are different. • Molarity is used so chemists can determine how many particles of a solute are available to react in a chemical reaction. • A 3. 0 M solution of A will have 3. 0 moles A per L of solution. © 2011 Pearson Education, Inc. Chapter 7 53

Percent (%) Three common units that use percent are: 1. Mass/volume percent 2. Mass/mass

$Math Matters: Percent (%) • A fraction can be converted to a percent by$

Math Matters: Percent (%) • A fraction can be converted to a percent by dividing the numerator by the denominator, multiplying by 100, and adding a percent sign. • A decimal number can be converted to a percent by multiplying by 100 and adding a percent sign. © 2011 Pearson Education, Inc. Chapter 7 55

Percent Mass/Mass, % (m/m) • When using % m/m in expressing concentration, it is important to realize that the mass of solute + mass of solvent = mass of solution. • Therefore, in the preparation of these solutions, the mass of both the solute and the solvent must be determined on a balance. © 2011 Pearson Education, Inc. Chapter 7 56

• This concentration unit can be determined by: • The unit % (m/m)

If 8. 0 g of glucose is mixed with 42. 0 g of water, the total mass of the solution is 50. 0 g (8. 0 g + 42. 0 g). The concentration of the resulting solution would be solved as follows: © 2011 Pearson Education, Inc. Chapter 7 58

Percent Volume/Volume, % (v/v) • This unit is typically used when liquids or gases are the solute. • For example, a bottle of wine that is 14% (v/v) alcohol means that 14 m. L of alcohol is present in 100 m. L of the wine. © 2011 Pearson Education, Inc. Chapter 7 59

This concentration unit can be determined by: © 2011 Pearson Education, Inc. Chapter 7

Percent Mass/Volume, % (m/v) • This concentration unit is often used in the preparation of intravenous fluids. Also known as percent weight/volume (% w/v). • For example, a solution of normal saline is 0. 9% (m/v), which means the solution contains 0. 90 g of Na. Cl in 100 m. L of solution. © 2011 Pearson Education, Inc. Chapter 7 61

Relationship to Other Common Units • The unit for measuring hemoglobin (oxygen carrying protein) in blood is g/d. L, which is the same as % (m/v). A d. L is the same as 100 m. L. • A common unit for measuring molecules, like glucose and cholesterol, in blood is mg/d. L, which is the same as mg% (milligram percent). © 2011 Pearson Education, Inc. Chapter 7 63

Parts per Million (ppm) and Parts per Billion (ppb) • Parts per million and parts per billion are concentration units for very dilute solutions. • How small is a part per million? There a million pennies in $10, 000, so one penny is a ppm of $10, 000. Or five drops of food coloring in a bathtub of water is about one part per million. © 2011 Pearson Education, Inc. Chapter 7 64

• How small is a part per billion? One drop of food coloring in an Olympic size swimming pool is about one part per billion. • Fluoride is added to water at 4 ppm to promote strong teeth, which means 4 g of fluoride are in every million m. L of tap water. • The maximum contaminant level of lead in water is 15 ppb, which means 15 g of lead are in every billion m. L of tap water. © 2011 Pearson Education, Inc. Chapter 7 65

• The unit of ppm is referred to as 1 mg/L and ppb is referred to as 1 μg/L. • Multiplying a solution, given in g solute/m. L solution, by one million will provide a concentration in ppm. Similarly, multiplying by one billion will provide a concentration in ppb. © 2011 Pearson Education, Inc. Chapter 7 66

© 2011 Pearson Education, Inc. Chapter 7 67

7. 5 Dilution • To prepare a solution of low concentration, you can dilute a solution of higher concentration. • For example, if you add water to a can of concentrated orange juice, the amount of orange juice does not change even though you have more solution present. • The amount of solute stayed the same, but the volume increased, so the concentration of the solution decreased. © 2011 Pearson Education, Inc. Chapter 7 68

• Mathematically, a dilution equation can be expressed as seen in the following equation: • Cinitial is the initial concentration, Cfinal is the final concentration, Vinitial is the initial volume, and Vfinal is the final volume. If any three of the four are known, then the fourth can be determined. © 2011 Pearson Education, Inc. Chapter 7 69

For example, if 150 m. L of 0. 90% saline is diluted to a final volume of 450 m. L with water, what would the concentration of the final diluted concentration be? © 2011 Pearson Education, Inc. Chapter 7 70

7. 5 Dilution, Continued • The dilution equation works for any concentration unit where the amount of solution is expressed in volume units. • This equation will not work with % m/m. • Dilution of pharmaceuticals are often prepared using this dilution equation. © 2011 Pearson Education, Inc. Chapter 7 71

7. 6 Osmosis and Diffusion Osmosis • Aqueous solutions are found inside and outside cells. The concentration of these solutions is highly controlled by the cells. • These solutions are separated by a semipermeable membrane called the cell membrane. • A semipermeable membrane allows some molecules to pass through the barrier. © 2011 Pearson Education, Inc. Chapter 7 72

• These solutions are considered to be isotonic solutions, meaning that the concentrations of solutes in the solutions is the same on both sides of the membrane. • Let’s examine why there is a limit to the amount of water a person can drink. A person can drink too much water, and it is recommended that a person drink between eight to twelve 8 -ounce glasses of water a day. © 2011 Pearson Education, Inc. Chapter 7 73

• Individuals engaging in vigorous exercise and infants whose formula is overly diluted can drink too much water. • The concentration of dissolved solutes in tap water or dilute formula is lower than the concentration of dissolved solutes in the body’s internal solution, so drinking large amounts of tap water will dilute the blood. © 2011 Pearson Education, Inc. Chapter 7 74

• When the blood is diluted, the concentration of solutes in the blood goes down. This causes an imbalance in the concentration of solutes inside and outside the cells. • The concentration of solutes outside the cell is low, while the concentration inside the cell is high. • When this happens, the solution outside the cells is said to be a hypotonic solution. © 2011 Pearson Education, Inc. Chapter 7 75

7. 6 Osmosis and Diffusion, Continued • When the concentrations outside and inside the cell are different, water will travel across the cell membrane in an attempt to equalize the concentrations. • The passage of water across the cell membrane is known as osmosis. • When an individual drinks too much water, hyponatremia (low sodium concentration) can occur from the bloodstream becoming dilute. © 2011 Pearson Education, Inc. Chapter 7 76

7. 6 Osmosis and Diffusion, Continued • If too much water enters the cell in an attempt to equalize solute concentrations, the cells will swell up and could burst. This bursting of cells is known as lysing. • When water enters the cell through osmosis, the water molecules exert a certain amount of pressure on the membrane known as osmotic pressure. © 2011 Pearson Education, Inc. Chapter 7 77

If the solute concentration is more concentrated on one side of a cell membrane, water molecules will cross the membrane in an attempt to equalize the concentrations on either side, and, as a result, the higher the osmotic pressure. © 2011 Pearson Education, Inc. Chapter 7 78

• Why does someone not want to drink salt water to quench their thirst? • Concentration of dissolved salts in salt water are higher (about three times higher) than the concentration of dissolved solutes inside the cell. • When salt water is consumed, it draws water out of the cells through osmosis to equalize the concentrations. This dehydrates cells. © 2011 Pearson Education, Inc. Chapter 7 79

• If salt water is consumed, the concentration of solutes outside the cells is higher than those inside the cell. • The solution outside the cells is said to be a hypertonic solution. During dehydration, the cells shrivel in a process known as crenation. © 2011 Pearson Education, Inc. Chapter 7 80

7. 6 Osmosis and Diffusion, Continued © 2011 Pearson Education, Inc. Chapter 7 81

7. 6 Osmosis and Diffusion, Continued • Consider the following illustration. • Net flow of water is from the lower concentration solution to the higher concentration of solution in order to equalize the concentrations. © 2011 Pearson Education, Inc. Chapter 7 82

• Because cell membranes are semipermeable, osmosis is an ongoing process. This process is used to maintain the concentrations of solutes at about the same level inside and outside the cells. • Solutions delivered into patients’ bloodstreams are isotonic, which minimizes osmosis. • Physiological solutions exert the same osmotic pressure as the cells and are isotonic. • Common physiological solutions are 0. 90% (m/v) Na. Cl, more commonly known as normal saline, and 5% (m/v) D-glucose (dextrose) referred to as D 5 W (5% dextrose in water). © 2011 Pearson Education, Inc. Chapter 7 83

Diffusion and Dialysis • Diffusion occurs when there is a net movement of molecules

7. 6 Osmosis and Diffusion, Continued • Diffusion is illustrated below. • Here, a drop of green food coloring is added to a beaker of water. Over time, the green dye molecules will diffuse throughout the water, and the resulting solution will have a uniform green color. © 2011 Pearson Education, Inc. Chapter 7 85

7. 6 Osmosis and Diffusion, Continued Kidney Dialysis • One place where diffusion occurs is in the kidneys. • Kidneys act to remove water molecules out of blood through diffusion across the membranes in the kidneys. • Larger molecules, like proteins, are too large to pass the membrane and get reabsorbed in the blood. © 2011 Pearson Education, Inc. Chapter 7 86

7. 6 Osmosis and Diffusion, Continued • Smaller molecules like urea diffuse out of the blood and move into urine in a process known as dialysis. • If the kidneys cannot remove waste products like urea, increased levels of the waste products increase in the bloodstream and can become life -threatening. • A person whose kidneys have failed can undergo artificial dialysis called hemodialysis. © 2011 Pearson Education, Inc. Chapter 7 87

• During hemodialysis, blood is removed from the patient and passes through one side of a semipermeable membrane in contact on the opposite side with a dialyzing solution that is isotonic with normal blood solute concentrations. • Waste products in the blood will then diffuse out of the passing blood and into the dialyzing solution, and the dialyzed blood returns to the patient. © 2011 Pearson Education, Inc. Chapter 7 88

© 2011 Pearson Education, Inc. Chapter 7 89

Objectives for Today ü ü Calculate concentration in different units Dilution Equation Osmosis and Diffusion Cell membranes (possible) Chapter 7 90

Objectives for Today q q How cell membranes work Chapter review Chapter 7 91

7. 7 Transport Across Cell Membranes • How do polar molecules, like glucose, and ions, like sodium ions, move across cell membranes? • Recall that the cell membrane’s main structural components are the phospholipids, which have a polar head containing a phosphate and a nonpolar part containing long hydrocarbon tails. © 2011 Pearson Education, Inc. Chapter 7 92

The arrangement of the cell membrane is shown in the following figure. © 2011

• • Ions, nonpolar molecules, and polar molecules move across cell membranes in different ways. There are three forms of transport across membranes: 1. Passive diffusion is simple diffusion. It does not require energy. Small molecules and nonpolar molecules like O 2, N 2, and CO 2 use this process. 2. Facilitated transport occurs when small molecules and ions pass through a channel formed by integral membrane proteins. It does not require energy. © 2011 Pearson Education, Inc. Chapter 7 94

© 2011 Pearson Education, Inc. Chapter 7 95

3. Active transport occurs when ions and small molecules move across the membrane in the opposite direction of diffusion. They require the assistance of a protein channel or pump. Energy expenditure in the form of adenosine triphosphate (ATP) is required. © 2011 Pearson Education, Inc. Chapter 7 96

Chapter Summary 7. 1 Solutions Are Mixtures • Solutions form when a solute dissolves in solvent. • Particles of solutes are evenly distributed. • A solute and a solvent may be a liquid, a solid, or a gas. • Solutions are transparent. • Mixtures that have particles suspended in a solution are called colloids. They are not transparent. Particles will settle upon standing. © 2011 Pearson Education, Inc. Chapter 7 97

Chapter Summary, Continued 7. 2 Formation of Solutions • Solvation occurs when solute particles are surrounded by solvent molecules and are interacting through attractive intermolecular forces. • Saturated solutions contain the maximum amount of solute dissolved in a solvent. • A saturated solution reaches an equilibrium where the rate of dissolving and reforming crystals is the same. • An increase in temperature increases the solubility of most solutes in water, but decreases the solubility of gases. Chapter in water. © 2011 Pearson Education, Inc. 7 98

Chapter Summary, Continued 7. 3 Chemical Equations for Solution • Substances that release ions in solution are called electrolytes because they conduct electricity. • Strong electrolytes completely dissociate in water. • Weak electrolytes partially dissociate in water. • Nonelectrolytes are substances that dissolve in water, but do not dissociate and do not conduct an electrical current. © 2011 Pearson Education, Inc. Chapter 7 99

Chapter Summary, Continued 7. 3 Chemical Equations for Solution Formation, Continued • The amount of dissolved ion in fluids is expressed by a unit known as an equivalent. • The number of equivalents present per mole of an ion is equal to the charge on that ion. © 2011 Pearson Education, Inc. Chapter 7 100

Chapter Summary, Continued 7. 4 Concentrations • Concentration is the amount of solute dissolved in a given amount of solution. • Fluid replacement solutions are expressed as m. Eq/L or in mmole/L. • Molarity is the number of moles of solute per liter of solution. • Other concentrations are: percent mass/volume; percent mass/mass, and percent volume/volume. Parts per million and parts per billion are used to express very dilute solutions. © 2011 Pearson Education, Inc. Chapter 7 101

Chapter Summary, Continued 7. 5 Dilution When a solute is diluted, the amount of solute stays the same, and the volume increases. As a result, the concentration of the solute decreases. © 2011 Pearson Education, Inc. Chapter 7 102

Chapter Summary, Continued 7. 6 Osmosis and Diffusion • During osmosis, water passes through a semipermeable membrane from a solution of lower concentration to a solution of higher solute concentration. • The osmotic pressure exerted on the membrane is directly related to the number of water molecules pushing against the membrane. • Isotonic solutions have osmotic pressures equal to those of bodily fluids. © 2011 Pearson Education, Inc. Chapter 7 103

Chapter Summary, Continued 7. 6 Osmosis and Diffusion, Continued • Cells maintain their volume in an isotonic solution. They will lyse in a hypotonic solution and shrink (crenate) in a hypertonic solution. • During dialysis, water and small molecules pass through a membrane in a related process called diffusion. Large particles do not pass through the membrane. © 2011 Pearson Education, Inc. Chapter 7 104

Chapter Summary, Continued 7. 7 Transport Across Cell Membranes • A semipermeable membrane separates the contents of a cell from the external fluids. • Membranes are composed of a lipid bilayer of phosholipids. The inside of the bilayer is nonpolar, while the exterior of the bilayer is polar. • Molecules are moved in and out of the cell by three transport processes known as passive transport, facilitated transport, and active transport. © 2011 Pearson Education, Inc. Chapter 7 105

Objectives for Today ü ü How cell membranes work Chapter review Chapter 7 106