Introduction to Biochemistry

Chapter 1 Introduction to Biochemistry At the end of the lesson, you should be able to: 1. Explain the uses and importance of Biochemistry 2. Describe the different chemical basis of life 3. Summarize the relationship of the different chemic...

Chapter 1 Introduction to Biochemistry At the end of the lesson, you should be able to: 1. Explain the uses and importance of Biochemistry 2. Describe the different chemical basis of life 3. Summarize the relationship of the different chemicals in the body and how it affects body function. Lesson 1. What is the definition of biochemistry? Biochemistry is the area in the life sciences which pre-eminently offers insight into the continuous and mainfold changes that occur in the organisms. It shows substances to be not static but ever changing in structure as well as function. The cell, including the cell membrane, as well as tissues and organisms are structures in flux. Biochemistry is concerned with the chemistry of living organisms. Organisms function as a whole and biochemical reaction processes are inter-related as a consequence. If we can relate the individual processes to the whole of the organism, we remain aware of the coherence of the substance flow and do more justice to the laws of life. The ultimate goal of biochemistry is to explain all life processes in molecular detail. Because life processes are performed by organic molecules, the discipline of biochemistry relies heavily on fundamental principles of organic chemistry and other basic sciences. Lesson 1.2 : The Chemical Basis of Life The biomolecules such as proteins that are present in living organisms are carbon-based compounds. Carbon is the third most abundant element in living organisms (relative abundance H > O > C > N > P > S). The most common ions are Ca+2, K+ , Na+ , Mg+2, and Cl-. The properties of biomolecules, such as shape and chemical reactivity, are best described by the discipline of organic chemistry. A. Representations of molecular structures. Your text will use skeletal, ball & stick, and space-filling models to show molecular structures. Therefore, you must be familiar with each of these types of representations. Skeletal & ball & stick models are good for showing the positions of nuclei in organic compounds. Space-filling models show van der Waals radii of the atoms in molecules, From left to right : Stick and ball model of Oxygen and water B. Chemical bonding. The atomic and molecular (bonding) orbitals of carbon, nitrogen, and oxygen,sp3 and sp2 molecular orbitals are the most prevalent in biomolecules. The orientations of bonding orbitals in space ultimately determine the shapes of biomolecules. From left to right : Sample molecular orbitals of Nitrogen and Oxygen Source :butane.chem.uiuc.edu C. Functional groups. The chemical reactions of biomolecules are dictated by the functional groups they contain. The figure below shows the general formulas of common organic compounds and functional groups that will be encountered constantly in the proteins, carbohydrates, nucleic acids and simple metabolites you will study. You should be familiar with the structure, charge properties, polarity, and basic chemical reactivity of all of these compounds and functional groups.  Image showing some of the known functional groups Lesson 1.3 : Many biomolecules are polymers. The principle biomolecules in cells (proteins, polysaccharides, and nucleic acids) are polymer chains of amino acids, monosaccharides, and nucleotides, respectively. Biopolymers are formed by condensation reactions in which water is removed from the reacting monomer units. Each monomer unit of a biopolymer is referred to as a residue. A. Proteins. Most of the chemical reactions of the cell are carried out by proteins. Proteins also are the major structural components of most cells and tissues. Proteins are often called polypeptides in reference to the fact that they are composed of amino acids held together by peptide bonds. Peptide bonds actually are amide bonds which are formed by the condensation of the carboxyl groups and amino groups of consecutive amino acids in the polymer chain. The so called peptide backbone of a protein is a monotonous, regularly repeating structure. Projecting out from the backbone are the R-groups which are the side-chains of the amino acids. In a later chapter, we will discuss how the R-groups play a significant role in determining the 3D structure of a protein, i.e., its active conformation. The enzymes comprise one subclass of proteins. These proteins carry out chemical reactions with extraordinary specificity and speed (up to 1017-fold enhancement in reaction rate). Specificity is achieved because the binding site for reactants--the active site--is highly complementary in shape to the reactants and products. This enzyme binds to and cleaves the polysaccharide portion of the bacterial cell wall. Cleavage leads to osmotic lysis of the affected bacterium. Lysozyme is present in tears and egg whites where it helps protect against unwanted bacterial growth and infection. We will discuss the structure and function of many medically and otherwise relevant proteins and enzymes such as myoglobin, hemoglobin, collagen, trypsin, insulin receptor, glycogen phosphorylase, plasma lipoproteins, and DNA polymerase in this course. Many of these proteins and enzymes are the targets of poisons and drugs whose actions also will be discussed. Sample protein with peptide bond(Source:Khan Academy) B. Polysaccharides. Polysaccharides are polymers of simples sugars known as monosaccharides (e.g., glucose). Different polysaccharides perform either structural (cellulose) or energy storage (glycogen, starch) functions. Polysaccharide and monosaccharides were some of the first biomolecules that were studied by organic chemists. A comparison of the polysaccharides starch and cellulose provides an excellent example of how structure is crucial to biological function. Namely, the structure of the glycosidic bonds linking the glucose units in cellulose and starch are very similar, yet the subtle difference in bond configuration determines whether the polymer is digestible (starch) or not (cellulose). From left to right :structure of a polysaccharide strach and a cellulose C. Nucleic acids. Nucleic acids are composed of nucleotide monomer units. Nucleotides themselves are composed of a monosaccharide, a nitrogenous base, and one or more phosphate groups. The nucleotide ATP is the major energy currency of the cell which is used to power a huge variety of energy-requiring reactions. ATP and other ribonucleotides (containing ribose) also make up the biopolymer RNA. Deoxyribonucleotides (containing deoxyribose) make up DNA. All nucleotides are held together by phosphodiester linkages where one phosphate group is attached to 2 sugar units in the backbone of the polymer.Nucleotides play key roles in information transfer in all organisms (DNA → RNA → protein). RNA also can carry out structural and enzymatic functions. For example, the formation of peptide bonds during protein synthesis actually is performed by one of the RNA constituents of the ribosome. In addition the main structural component of ribosomes is RNA. Lastly, a number of nucleic acid analogs are used to inhibit DNA synthesis and are extremely important in management of cancers and virally caused diseases such as AIDS. Comparison of DNA and RNA with the components of a nucleotide D. Lipids and membranes. Lipids are a diverse collection of biomolecules that are composed mostly of carbon and hydrogen, i.e., hydrocarbons. Lipids contain relatively few polar functional groups. They typically are more soluble in organic solvents than in water. The primary building block of many lipids is a fatty acid. The most common structural lipid in cell membranes--glycerophospholipid- -contains 2 fatty acids, glycerol and a polar head group. When collected as assemblies of millions of molecules, the classical biological structure known as a membrane is formed. Biological membranes usually contain proteins, and protein content and composition is highly variable and determined by membrane function. Although discussed here along with true biopolymers, membranes are actually molecular aggregates. Lesson 1.4 : The energetics of life. Living organisms are highly complicated at the molecular level. A large amount of energy is invested in maintaining the ordered and complicated state of cells and tissues. In humans and animals, energy needed for work and biosynthesis of cellular structures is derived from organic molecules in the diet. Often these come from plant sources, who derived their energy for synthesis of biomolecules from sunlight. In animals, energy is derived from the breakdown of fuel molecules by processes referred to as catabolism. In turn, the energy released from catabolism is used to drive biosynthetic processes collectively referred to as anabolism. Most of our use of thermodynamics will be concerned with the calculation of free energy changes (∆G) which can be used to determine the direction of metabolic reactions and their equilibrium constants. ∆G values are determined by the enthalpy (∆H, heat transfer) and entropy (∆S, change in randomness) changes associated with a reaction through the equation ∆G = ∆H - T∆S. Negative values of ∆G signify favorable reactions, whereas positive values of ∆G are associated with unfavorable reactions. Keq is based on the DG value and gives the ratio of products to reacts once equilibrium is reached. This is important because it will show how a cell can ratio reactions in different directions. Kinetics measures the rate at which a reaction takes place and how the reaction gets from start to finish. So reactions can be thermodynamically favorable but kinetically unfavorable. So cells use enzymes that can only affect the kinetics not the thermodynamics. Bioenergetics is one of the tools used in animal and human nutrition. Weight gain or loss ultimately depend on the difference between caloric intake and expenditure. In this course, we will discuss energy metabolism in different physiological states such as exercise and fasting, and in diseases such as diabetes. Biochemistry and evolution Biochemistry has greatly extended our knowledge of phylogeny and evolution that was acquired originally through the disciplines of comparative anatomy, population genetics and paleontology. In fact, only through biochemistry have we come to appreciate that all living organisms are similar at the molecular level. Namely, they share similar means of replication, cellular structure, and often energy utilization & production. For this reason, much of what we can learn about simple organisms such as Escherichia coli can be applied to the study of higher organisms such as us. The similarity of organisms at a molecular level indicates that all are derived from a common ancestor. Carl Woese determined by comparisons of ribosomal RNA (rRNA) sequences that it is possible to construct a highly accurate tree of life showing the evolutionary relationship between all life forms. rRNA analysis has proven that living organisms are best divided into 3 domains of life--the Archaea, the Bacteria, and the Eukarya. At the end of the course we will discuss the properties of one of the most important enzymes used in modern biochemistry laboratories, Taq polymerase. This enzyme is derived from the Archaean species Thermus aquaticus, which was isolated from a hotspring located in Yellowstone Natl. Pk. One common use of this enzyme is in sequencing rRNA genes from newly isolated microorganism  Chapter 2 Introduction to the Cell At the end of the lesson, you should be able to: 1. Describe the structure of the different organelles and explain the function of each 2. Explain the importance of cell functions and processes 3. Compare and contrast the structure of the cell as to its function. The study of the cell is an important in the study of chemistry. Knowledge of Chemistry makes it possible to understand cells because cells are composed of chemicals, and those chemicals are responsible for many of the cell’s characteristics. Cells, in turn, determine the form and functions of the human body. From cellular function, we can progress to the study of tissues. In addition, many diseases and other human disorders have a cellular basis. The human body is composed of trillions of cells and acts as host to countless other organisms. The cell is the basic unit of all organisms. The simplest organisms consist of single cells, whereas humans are composed of multiple cells. The cells may be small in size but cells are complex living structures. Cells have many characteristics in common:however, most cells are also specialized to perform specific functions. The human body is made up of may populations of specialized cells. The coordinated functions of these populations are critical to the survival of humans and all other complex organisms. Each cell is a highly organized unit. Within cells, specialized structures called organelles perform specific functions. The nucleus is an organelle containing the cell’s genetic material. The living material surrounding the nucleus is called cytoplasm and it contains many types of organelles. The cytoplasm is enclosed by the cell membrane or plasma membrane. The number and type of organelles within each cell determine the cell’s specific structure and function. For example, cells secreting large amount of protein contains well-developed organelles that synthesize and secrete protein, whereas muscle cells contain proteins and organelles that enable them to contract. Figure 1 : Generalized cell  Table 1 : The Cell organelles and their locations and functions Functions of the Cell Cells are the smallest unit that have all the characteristics of life. Our body cells perform several important functions: 1. Cell mechanism and energy use. The chemical reactions that occur within the cells are collectively called metabolism. Energy released during metabolism is used for cell activities such as the synthesis of new molecules, muscle contraction and heat production which helps maintain body temperature. 2. Synthesis of molecules. Cells synthesize various types of molecules, including proteins, nucleic acids and lipids. The different cells of the body do not all produce the same molecules. Therefore, the structural and functional characteristics of cells are determined by the types of molecules they produce. 3. Communication. Cells produce and receive chemical and electrical signals that allow them to communicate with one another and with muscle cells causing muscle cells to contact. 4. Reproduction and inheritance. Each cell contains a copy of the genetic information of the individual. Specialized cells transmit that genetic information to the next generation.  Chapter 3 Water, The Medium of Life At the end of the lesson, you should be able to: 1. Describe the molecular structure of water 2. Compare the physical and chemical properties of water 3. List down the importance of water You are probably already familiar with many of the water’s properties. For example, you no doubt know that water is tasteless,odorless and transparent. In small quantities, it is also colorless. However, when a large amount of water is observed, as in a lake or ocean, it is actually light blue in color. The blue hue of the water is an intrinsic property and is caused by selective absorption and scattering of light. These and other properties of water depend on its chemical structure. The transparency of water is important for organisms that live in water. Because water is transparent, sunlight can pass through it. Sunlight is needed by water plants and other organisms for photosynthesis. Chemical Structure of Water Each molecule of water consists of one atom of oxygen and two atoms of hydrogen,so it has the chemical formula H2O. The arrangement of atoms in a water molecule explains many of the water’s chemical properties. In each water molecule, the nucleus of the oxygen atom attracts electron much more strongly than do the hydrogen nuclei. This results in a negative electrical charge near the oxygen atom and a positive electrical charge near the hydrogen atoms. A difference in electrical charge between parts of a molecule is called polarity. A polar molecule is a molecule in which part of the molecule is positively charged and the part of the molecule is negatively charged. Figure 1 : This model is an atomic diagram of water, showing two hydrogen atoms and an oxygen atom in the center. Water is a good solvent Water is considered a very good solvent in biochemical reactions. Table salt (NaCl) consists of a positively charged sodium ion and a negatively charged chloride ion. The oxygen of water is attracted to a positive Na ion. The hydrogens of water are attracted to the negative Cl ion. Figure 2 : This diagram shows the parts of water molecule. It also depicts how a charge, such as on an ion can interact with a water molecule. Hydrogen Bonding Opposite electrical charges attract one another. Therefore, the positive part of one molecule is attracted to a negative parts of other water molecules. Because of this attraction, bonds form between hydrogen and oxygen atoms of adjacent water molecules. This type of bond always involves a hydrogen atom , so it is called hydrogen bond. Hydrogen bond can also form within a single organic molecule. For example, hydrogen bonds that form between different parts of a protein molecule bend the molecule into distinctive shape, which is important for the protein’s functions. Hydrogen bonds also held together the two nucleotide chains of a DNA molecule.  Figure 3 : Hydrogen bonds form between positively and negatively charged parts of water molecule. The bonds hold the water molecules together. Properties of Water Water has some unusual properties due to its hydrogen bonds. One property is cohesion, the tendency for water molecules to stick together. The cohesive forces between water molecules are responsible for the phenomenon known as surface tension. The molecules at the surface do not have other like molecules on all sides of them and consequently, they cohere more strongly to those directly associated with them on the surface. For example, if you drop a tiny amount of water onto a very smooth surface, the water molecules will stick together and form a droplet, rather than spread out over the surface. The same thing happens when water slowly drips from a leaky faucet. The water doesn’t fall from the faucet as individual water molecules but as droplets of water. The tendency of water to stick together in droplets is also illustrated by the dew drops. Figure 4 : From left to right,an image showing how cohesion and surface tension works Another important physical property of water is adhesion. In terms of water, adhesion is the bonding of water of a water molecule to another substance such as the sides of the leaf’s veins. This process happens because hydrogen bonds are special in that they break and reform with great frequency. This constant rearranging of hydrogen bonds allows a percentage of all molecules in a given sample to bond to another substance. This grip-like characteristics that water molecules form causes capillary action, the ability of a liquid to flow against gravity in a narrow space. An example of capillary action is when you place a straw into a glass of water. The water seems to climb up the straw before you even place your mouth on the straw. The water has created hydrogen bonds with the surface of the straw, causing the water to adhere to the sides of the straw. As the hydrogen bonds keep interchanging with the straw’s surface, the water molecules interchange positions and some begin to ascend the straw.  Figure 5 (From left to right) : An image showing adhesion and capillary action works Adhesion and capillary action are necessary to the survival of most organisms. It is the mechanism that is responsible for water transport in plants through roots and stems. In animals, through small blood vessels. Hydrogen bonds can also explain why water’s boiling point is higher than the boiling points of similar substances without hydrogen bonds. Because of water’s relatively high boiling point, most water exists in a liquid state on Earth. Liquid water is needed by all living organisms. Therefore the availability of liquid water enables life to survive over much of the planet. Furthermore, water has a high specific heat because it takes a lot of energy to raise or lower the temperature of the water. As a result, water plays a very important role in temperature regulation. Since cells are made up of water, this property helps to maintain homeostasis. The density of ice and water The melting point of water is 0 degree celcius. Below this temperature, water is a solid. Unlike most chemical substances, water as a solid state has a lower density than water in a liquid state. This is because water expands when it freezes. Again, hydrogen bonding is the reason. Hydrogen bonds cause water molecules to line up less efficiently in ice than in liquid water. As a result, water molecules are spaced farther apart in ice, giving ice a lower density than liquid water. A substance with lower density floats on a substance with higher density. This explains why ice floats on liquid water, whereas many other solids sink to the bottom of liquid water. In a large body of water, such as th elake or ocean, the water with the greatest density always sinks to the bottom. Water is most dense at about 4 degree celcius. As a result, the water at the bottom of a lake or the ocean usually has a temperature of about 4 degree celcius. In climates with cold winters, this layer of 4 degree celcius water insulates the bottom of a lake from freezing temperatures. Lake organisms such as fish can survive the winter by staying n this cold, but unfrozen water at he bottom of the lake. Figure 6 : A comparison of the molecular structure of ice and liquid water Lesson 3.1 : Thermal Properties of Water Water has a unique thermal properties that enable it to exist in three different states: vapor,solid and liquid under environmentally relevant conditions. Changes in each phase have certain terminology depending upon the state changes ,as described below: Condensation : vapor to liquid Evaporation : liquid-vapor Freezing : liquid to solid Melting :solid-liquid Sublimation : solid-vapor Frost formation : vapor to solid Most liquids contract with decreasing temperature. This contraction also makes these liquids denser as temperature decreases. Water is unique because its density increases only down to approximately 4 degree Celsius, at which point it starts to become less dense. This is important because without this unique property, icebergs and other solid forms of water would sink to the bottom of the ocean, displacing liquid water as they did so. Also, lakes and ponds would freeze from the bottom up with the same effect. Figure 1 : The Density of water at varying temperatures The following are the thermal properties of water 1. The specific heat. The specific heat of water is the amount of energy required to raised one gram of water to one degree Celsius and is usually expressed as joules per gram-degree Celsius or J/g ℃. specific heat values for the different phases of water are given below: Phase J/g ℃. Liquid 4.18 Solid 2.06 Vapor 2.02 2. The latent heat of fusion. It is the amount of energy required to change 1 gram of ice at its melting point temperature to liquid. It is considered latent because there is no temperature change associated with this energy transfer, only a change in phase. The heat of fusion of water is -333 J/g ℃. the energy required for the phase changes of water are given in the table below: Process From To Energy gained or lost( J/g ℃.) Condensation vapor liquid 2500 Deposition vapor ice 2833 Evaporation liquid vapor -2500 Freezing liquid ice 333 Melting ice liquid -333 Sublimation ice vapor 2833 At the melting point of ice, temperature remains constant. The energy absorbed is used to break the bonds that hold the water molecules in the solid structure of ice. The heat absorbed to melt one gram of ice to one gram of water is the heat of fusion of ice,ΔHfus. When water turns Into ice,heat is released. The amount use of heat given up or released when one gram of water changes to one gram of ice is the heat of solidification of water ΔH sol. Since melting and freezing are reverse processes, the heat of fusion and heat of solidification are equal but opposite in signs.  +333.6 J/g Ice Water *The positive sign indicates that heat is absorbed while the negative sign indicates that heat is released. For ice, 333.6 joules of energy is required to melt 1 g of ice(solid) to -333.6 J/g liquid(water) or 6.01 kilojoules(kJ) per mole 0℃. Heat of fusion( 0℃.) = 333.6 J / g(ice) 3. Heat of vaporization. The energy absorbed to change 1 g of liquid to gas at its boiling point is called the heat of vaporization,ΔHvap. When a vapor condenses to liquid, the opposite transfer of heat occurs. The heat is released when 1 gram of a gas condenses to a liquid at its boiling point is the heat of condensation. Since vaporization and condensation are reverse processes,the heat of vaporization and the heat of condensation of a substance are equal but opposite in signs. +2258 J/g *The following may be used in calculations of heat transfer Water steam(vapor) of water: Specific heat of ice - 2.04 J/g ℃ -2258 J/g Specific heat of water - 4.18 J/g ℃ Specific heat of steam - 2.00 J/g ℃ Heat of fusion of water (0℃) - 333.6 J/g Heat of vaporization of water(100℃) - 2258 J/g Earth is unique because it contains the necessary temperatures and pressures for all these three states of water to exist. Water, under correct combination of temperature and pressure,is capable of existing in all three states simultaneously and in equilibrium. This is referred to as the triple point, where infinitesimally small increases or decreases in either pressure or temperature will cause water to be either liquid,solid or gas. Specifically, the triple point of water exists at a temperature and pressure of 273.16 Kelvin(0.0098 ℃) and 611.73 pascals*(0.00603 atm) respectively. The increasing pressure causes water to pass directly from a gas to a solid. At pressures higher than the triple point, increasing temperature causes solid water to transform into liquid and eventually gas. Liquid water cannot exists in pressures lower than the triple point and ice simultaneously becomes steam with increasing temperature. This process is known as sublimation. Figure 2 : Phase Diagram of the triple point of water  Chapter 3 Water,Medium of Life At the end of the lesson, you should be able to: 1. Differentiate the ways of expressing solutions 2. Compute for the unknown values in a given problem 3. State the importance of knowing how to express solutions Lesson 3.1 : Though its known that water dissolves almost all of solutes, oftentimes solvent aside from water is used to dissolve other solutes. Thus, it can be said that solutions can be gaseous,liquid or solid based on their physical properties. Types Examples Solute Solvent Gaseous solutions Gas in gas Air Oxygen and other gases Nitrogen Liquid solutions Gas in liquid Soda water Carbon dioxide Water Liquid in liquid Antifreeze Ethylene glycol Water Solid in liquid Sea water Sodium chloride Water Solid solutions Liquid in solid Dental amalgam Mercury Silver Solid in solid Steel Carbon Iron Gas in solid Charcoal filter Poisonous gases Carbon Gaseous Solutions The air we breath is considered to be an example of gaseous solutions for it contain mixture of different gases such as nitrogen,oxygen,argon and neon. Some pollutants such as SO2 and NO2 can be seen also in the atmosphere. Since nitrogen is considered to be the most abundant gas in the atmosphere it is considered to be the solvent as per the rule. Liquid solutions These are the most common type of solutions. Carbonated beverages and softdrinks are solutions of carbon dioxide and other components in water. Vinegar is acetic acid in water, antifreeze is ethylene glycol in water. Salt dissolve in water makes a liquid solution. Solid solutions Gold or sterling silver jewelry are examples of solid solutions. The most common solid solutions are combinations of two or more metals called alloys. Lesson 3.2 : Concentration of Solutions Solutions can be described qualitatively or quantitatively based on the amount of solute relative to a given amount of solvent. Qualitatively, we can describe solutions as either dilute or concentrated. A dilute solution contains relatively small amount of solute whereas a concentrated solution contains a relatively large amount of solute. For example, a solution containing 5 g of salt in 100 ml of water is dilute while a solution containing 40 g of salt in the same volume of water is concentrated. Below are the different ways of expressing the quantity of solute present in a given amount of solvent. 1. Parts per Million Parts per million(ppm) is a unit for expressing very dilute concentrations. It is commonly used to express the concentration of pollutants in air or in water. Components of gas mixtures present in very small amounts are usually expressed in parts per million by volume as defined by the equation, ppm= volume of component / total volume of solution x 106 ppm. If the solution is given in grams or mass unit, then you can simply change the volume units in the equation to mass units. Example: If 100 L of a gas mixture over a metropolitan area contains 0.0060 L of CO,what is the concentration in ppm of CO present? Given : Volume of pure gas - 0.0060 L Total volume of gas mixture - 100 L Unknown: ppm=? Formula: ppm= volume of component / total volume of solution x 106 ppm Solution: ppm = 0.0060 L / 100 L x 106 ppm Ppm = 60 ppm 2. Mass or volume percent One of the simplest ways to express concentration of solutions is by mass or volume percent. It is computed with the formula, mass % of component = mass of component in solution / total mass of solution x 100%. If the amounts of the component and the solution are given in terms of volume, change the mass units to volume units. The volume by volume percent(Vsolute / Vsolution)% is useful when dealing with liquid solutions. The volumes are usually given in mililiters. To express the alcohol content of wines and liquors,the term proof is used which is twice the volume percentage or the mass percentage of an alcohol. Example: A solution is prepared by dissolving 10 g of glucose C6H12O6 in 100 g of water. What is the percentage by mass of glucose in the solution? Given : mass of glucose = 10 g mass of solution = 100 g + 10 g Unknown: mass & of glucose Formula : mass % of glucose = mass of glucose / mass of solution x 100% Solution : mass % of glucose = 10 g / 100 g + 10 g x 100% =10 g/110 g x 100% = 9% Example: 15 mL of alcohol is mixed with 85 mL of water. Find the (a) percentage by volume of the solution and (b) proof of the solution A. (Vsolute /Vsolution)% = volume of alcohol / volume of solution x 100% = 15 mL / 15 mL+85 mL x 100% =15 % B. Proof = (Vsolute /Vsolution)% x 2 = (15%) x 2 = 30 3. Mole Fraction The three most commonly used to quantitative measures of concentration of solutions are mole fraction,molarity and molality. Mole fraction(X) is the ratio of the number of moles of one component(nA) to the total number of moles in the solution (nA + nB). mole fraction = moles of component / total moles of solution or XA =nA / nA + nB or XB = nB / nA +nB Example: Calculate the mole fraction of Phosphoric acid (H3PO4 ) in 30% aqueous Phosphoric acid solution. Assume that the solution is 100 g. Given : 30% Aqueous H3PO4 (30g H3PO4 ) Mass of solution is 100 g Unknown: mole fraction of H3PO4 Formula: mole fraction = moles of component / total moles of solution Solution: 30 g H3PO4 Molar mass = 98 g/mol 70 g of H2O Molar mass = 18 g/mol Moles of H3PO4 = 30 g H3PO4 (1 mol H3PO4 / 98 g H3PO4) = 0.31 mol Moles of H2O = 70 g H2O (1 mol H2O / 18 g H2O) = 3.9 mol Moles of solution = 0.31 mol + 3.9 mol = 4.21 mol Mole fraction = moles of H3PO4 / moles of solution = 0.31 mol / 4.21 mol = 0.074 4. Molarity(M) Is the most common way of expressing the concentration of solution. It is defined as the number of moles of solute per liter of solution. Molarity = moles of solute / liter of solution M = nsolute / Lsolution Example: A solution is prepared by dissolving 4.00 g of NaOH in 100 g of water. The volume of the resulting solution is 102 mL. Calculate its molarity. Given : L of solution = 102 ml = 0.102 L *Convert ml to L. Just divide it by 1000 Molar mass of NaOH = 40 g/mol Molar mass of H2O = 18 g/mol Unknown: M=? Formula: Mole fraction = moles of H3PO4 / moles of solution Solution: XNaOH = 4g NaOH (1mol NaOH / 40g NaOH) = 0.10 mol XH2O = 100g H2O (1mol H2O / 18g H2O) =5.55 mol M = mol solute / L solute = 0.10 mol / 0.102 L = 0.98 mol/L or 0.98 M 5. Molality(m) The molality of a solution is the number of moles of solute dissolved per kilogram of solvent where Molality(m) = moles of solute / kilogram of solvent or m = nsolute / kgsolvent.. Although molarity and molality are quite similar,notice that molarity is defined in terms of the volume of a solution whereas molality is defined in terms of the mass of a solvent. Example: Calculate the molality of a solution made by dissolving 65.2 g sucrose in a 500 ml water. Given: mass of solute= 65.2g Volume of solvent=500mL=500g=0.500kg Kg solvent=0.500kg Molar mass of sucrose=342g/mol Required: m=? Solution: m = 65.2 g (1 mol/342 g) / 0.500kg m = 0.1906mol / 0.500 kg m = 0.381 mol/kg or 0.381 m Lesson 3.3 : Dilution Stock solutions are concentrated solutions in laboratory with a known molar concentration and are diluted to a lower concentration for the actual use in the experiment or activity. In your experiments, you may need to prepare dilute solutions from concentrated solutions. Bear in mind that the number of moles of solute does not change when a solution is diluted. Number of moles of dilution = number of moles after dilution. From the definition of molarity: Molarity = moles of solute(n) / liter of solution(V); nsolute = M x V. Since the total number of moles of solute does not change,M1V1 = M2V2 where M1 and V1 are the molarity and the volume of the initial solutions respectively, and M2 and V2 are the molarity and volume of the final solution respectively. Example: How would you prepare a 0.1 M of HCl solution from 10 ml of a 0.5 M of HCL stock solution? Solution: M1V1 = M2V2; therefore, V2 = M1V1 / M2 substituting the values into the equation, V2 = ( 0. 5 M X 10 mL) / 0.1 M V2 = 50 ml