Analytical Chemistry First Grade PDF

Analytical Chemistry First Grade Dr. Hussein Fadhel Al- Rubaay 2025 First part 1  Lecture (1) Introduction to Analytical Chemistry Analytical chemistry is the branch of chemist...

Analytical Chemistry First Grade Dr. Hussein Fadhel Al- Rubaay 2025 First part 1  Lecture (1) Introduction to Analytical Chemistry Analytical chemistry is the branch of chemistry that deals with the analysis of different substances, and it involves the separation, identification, and the quantification of matter. by using of classical methods along with modern scientific instruments to achieve all these purposes. Analytical chemistry is often described as the area of chemistry responsible for: 1- Characterizing the composition of matter, both qualitatively and quantitatively. 2- Improving established analytical methods. 3- Extending existing analytical methods to new types of samples. 4- Developing new analytical methods for measuring chemical phenomena... The scope of analytical chemistry: The science seeks ever-improved means of measuring the chemical composition of natural and artificial materials by using techniques to identify the substances that may be present in a material and to determine the exact amounts of the identified substance. Analytical chemistry involves the analysis of matter to determine its composition and the quantity of each kind of matter that is present. Analytical chemists detect traces of toxic chemicals in water and air. A detection of the component in qualitative analysis can be the basis of the method or the procedure of its quantitative analysis. The reaction may be incomplete in qualitative analysis, while in quantitative analysis the reaction should be complete and give clear and known products. Analytical chemistry consists of: (A) Qualitative analysis: which deals with the identification of elements, ions, or compounds present in a sample (tells us what chemicals are present in a sample). (B)Quantitative analysis: which is dealing with the determination of how much of one or more constituents is present (tells how much amounts of chemicals are present in a sample). This analysis can be divided into three types: (1) Volumetric analysis (Titrimetric analysis): is measured the volume of a solution containing sufficient reagent to react completely with the analyte. (2) Gravimetric analysis: Gravimetric methods, determine the mass of the analyte or some compound chemically related to it. (3) Instrumental analysis: These methods are based on the measurement of physical or chemical properties using special instruments. These properties are related to the concentrations or amounts of the components in the sample. These methods are compared directly or indirectly with typical standard methods. These methods consist of: a) Spectroscopic methods: are based on measurement of the interaction between electromagnetic radiation and analyte atoms or molecules or on the production of such radiation by analytes (ultraviolet, visible, or infrared), fluorimetry, atomic spectroscopy (absorption, emission), mass 2  Lecture (1) spectrometry, nuclear magnetic resonance spectrometry (NMR), X-ray spectroscopy (absorption, fluorescence). a) Electroanalytical methods: involve the measurement of such electrical properties that wanted to be determined, such as pH measurements, electrodeposition, voltametry, thermal analysis, potential, current, resistance, and quantity of electrical charge. b) Separation methods: They mean the isolation of one component or more from a mixture of components in solid, liquid and gas cases. These methods are included with instrumental methods since the instruments and equipment's are used in separation processes. These methods involve precipitation, volatilization, ion exchange, extraction with solvent and various chromatographic methods. Modern analytical chemistry Modern analytical chemistry is dominated by instrumental analysis. There are so many different types of instruments today that it can seem like a confusing array of acronyms rather than a unified field of study. Many analytical chemists focus on a single type of instrument. Academics tend to either focus on new applications and discoveries or on new methods of analysis. The discovery of a chemical present in blood that increases the risk of cancer would be a discovery that an analytical chemist might be involved in. An effort to develop a new method might involve the use of a tunable laser to increase the specificity and sensitivity of a spectrometric method. Many methods, once developed, are kept purposely static so that data can be compared over long periods of time. This is particularly true in industrial quality assurance (QA), forensic and environmental applications. Analytical chemistry plays an increasingly important role in the pharmaceutical industry where, aside from QA, it is used in discovery of new drug candidates and in clinical applications where understanding the interactions between the drug and the patient are critical. The roles of analytical chemistry 1 It plays a vital role in the development of science.It has evolved from an art to a science with application throughout industry ,medicine and all science.To illustrate ,consider a few examples: a. The concentration of O 2and CO 2are determined in millions of blood samples every day and used to diagnose and treat illnesses. b. Quantitative measurement of ionized Ca in blood serum help diagnose parathyroid disease in human. c. Quantitative determination of N 2 in food establishes their protein content and thus their nutritional value. d. Quantitative analysis of raw materials and final product in the industrial production lines. 2 -Quantitative analytical measurements also play a vital role in many research areas in chemistry ,biochemistry ,biology ,geology and the other sciences ,for example: 3  Lecture (1) a. Quantitative measurements of K ,Ca and Na ions in the body fluids of animals permit physiologists to study the role of these ions in the nerve-signal conduction as well as muscle contraction and relaxation. b. Materials scientists rely heavily on quantitative analyses of crystalline germanium and silicon in their studies of semiconductor devices. Many chemists, biochemists, and medicinal chemists devote much time in the laboratory gathering quantitative information about system of interest to them. The central role of analytical chemistry in this enterprise and many others is illustrated in Figure (1). All branches of chemistry draw on the ideas and techniques of analytical chemistry. Chemistry is often termed the central science; and the top center position of chemistry as well as the center position of analytical chemistry in the figure symbolizes the importance of chemistry sciences. Analytical chemistry serves an essential tool in the entire field depicted in the figure. General steps in a chemical analysis 1- Define the problem. 2- Selecting analytical procedures( method.) 3 -Sampling( obtain sample.) 4 -Sample preparation( prepare sample for analysis.) 5 -Perform any necessary chemical separations. 6- Analysis( perform the measurement.) 7- Calculate the results and report 4  Lecture (2) Expressing of solution concentration We always discuss a solution being diluted or concentrated; this is a qualitative way of expressing the concentration of the solution. A dilute solution means the quantity of solute is relatively very small, and a concentrated solution implies that the solution has a large amount of solute. But these are relative terms and do not give us the quantitative concentration of the solution. Concentration It is the amount of solute present in one litre of solution. It is denoted by Mass Percentage (w/w): When the concentration is expressed as the percent of one component in the solution by mass it is called mass percentage (w/w). Suppose we have a solution containing component A as the solute and B as the solvent, then its mass percentage is expressed as: Mass % of A = A / A+ B* 100 Example: An aqueous solution contains 42% by mass ethanol. What mass of ethanol is present in 250 g of solution? Sol/ 1- Extract the data from the question: Aqueous solution is made up of two components, a solute (ethanol) and a solvent (water), mass % ethanol = 42 %, mass(solution) = mass(ethanol) + mass(water) = 250 g mass(ethanol) = ? g 2- Write the equation for finding mass % ethanol: mass % ethanol = mass(ethanol) ÷ mass(solution) × 100 Re-arrange the equation to find mass of ethanol: mass(ethanol) = mass % ethanol × mass(solution) ÷ 100 3- Substitute the values into the equation and solve: mass(ethanol) = 42 × 250 ÷ 100 = 105 g 5  Lecture (2) Volume Percentage (V/V): Sometimes we express the concentration as a percent of one component in the solution by volume, it is then called as volume percentage and is given as: It's the volume of solute present in 100 mL of solution. Volume of solute (ml) % V / v =-------------------------------- x 100 Volume of solution (ml) Example 2: A solution is prepared by dissolving 90 mL of hydrogen peroxide in enough water to make 3000 mL of solution. Identify the concentration of the hydrogen peroxide solution. Sol/ The given parameters are Volume of solute = 90 mL Volume of solution = 3000 mL Substitute the values in the given formula, Volume percent = volume of solute /volume of solution x 100% = 90 mL/ 3000mL x 100% Volume percent = 3 % Weight – Volume Percentage (% w/v) It's the amount of solute present in 100 mL of solution. 6  Lecture (2) % w/V = (Mass of component A in the solution/ Total Volume of the Solution)x 100 1. Concentration in Parts Per Million (ppm) The parts of a component per million parts (106) of the solution. Weight of solute (g) PPM =--------------------------------- x 10 6 Volume of Solution (ml) Relationship between PPM and Molarity and Normality PPM = M x M.Wt x 1000 PPM = N x Eq.Wt x 1000 Converting weight/volume (w/v) concentrations to ppm ppm = 1g/m3 = 1mg/L = 1μg/mL 1. A solution has a concentration of 1.25g/L. What is its concentration in ppm? a. Convert the mass in grams to a mass in milligrams: 1.25g = 1.25 x 1000mg = 1250mg b. Re-write the concentration in mg/L = 1250mg/L = 1250ppm 7  Lecture (2) 2. A solution has a concentration of 0.5mg/mL. What is its concentration in ppm? a. Convert the volume to litres: volume = 1mL = 1mL ÷ 1000mL/L = 0.001L b. Re-write the concentration in mg/L = 0.5mg/0.001L = 500mg/L = 500ppm Converting weight/weight (w/w) concentrations to ppm 1ppm = 1mg/kg = 1μg/g Mole Concept:- Mole: which is Avogadro’s number (6.0221023) of atoms, molecules, ions or other species. Numerically: it is the atomic, molecular, or formula weight of a substance expressed in grams. Or Mole: which is 1 mole is the amount of substance that contains as many particles (atoms or molecules) as there are in 12.0 g of C-12 Number of moles = (W) mass of sample (g) -1 (Mw) molar mass (gmol ) Molecular Weight = Sum. Of atomic weight 8  Lecture (2) Molarity (M): Molarity tells us the number of moles of solute in exactly one liter of a solution. (Note that molarity is spelled with an "r" and is represented by a capital M.) We need two pieces of information to calculate the molarity of a solute in a solution:  The moles of solute present in the solution.  The volume of solution (in liters) containing the solute. To calculate molarity we use the equation: Example 1. What is the molarity of a 5.00 liter solution that was made with 10.0 moles of KBr ? Solution: We can use the original formula. Note that in this particular example, where the number of moles of solute is given, the identity of the solute (KBr) has nothing to do with solving the problem. 9 Lecture (2) 10  Lecture (2) Normality is the number of equivalents of solute dissolved in one liter of solution. The units, therefore are equivalents per liter, specifically it's equivalents of solute per liter of solution. No. of equivalents of solute Normality = liter of solution Weight (g) No. of equivalents (n) =--------------------------- Equivalent Weight ( g/eq) n = No. of (H) atoms for acids for HCl n=1 n = No of OH groups for bases for NaOH n=1 n = No of Cation atoms (M+) for salts for Na2CO3 n= 2 n = No. of gained or lost electrons for oxidants and reductants for KMnO 4 n= 7 Molality (m): Molality, m, tells us the number of moles of solute dissolved in exactly one kilogram of solvent. (Note that molality is spelled with two "l"'s and represented by a lower case m.) We need two pieces of information to calculate the molality of a solute in a solution:  The moles of solute present in the solution.  The mass of solvent (in kilograms) in the solution. calculate molality we use the equation: Eq.Wt = M.Wt n N=Mxn Q / what is the normality of 0.1 mol /L of Na2SO4 ? N = 0.1 * 2 = 0.2 N 11  Lecture (3) Mole Fraction: The mole fraction, X, of a component in a solution is the ratio of the number of moles of that component to the total number of moles of all components in the solution. To calculate mole fraction, we need to know:  The number of moles of each component present in the solution. The mole fraction of A, XA, in a solution consisting of A, B, C,... is calculated using the equation: To calculate the mole fraction of B, XB, use: xA=nAnA+nB xB=nBnA+nB The above-mentioned methods are commonly used ways of expressing the concentration of solutions. All the methods describe the same thing that is, the concentration of a solution, each of them has its own advantages and disadvantages. Molarity depends on temperature while mole fraction and molality are independent of temperature. All these methods are used on the basis of the requirement of expressing the concentrations. Solutions. Solution: Homogeneous mixture of two or more substance produce from dissolved (disappeared) solute particle (ions, atoms, molecules) (lesser amount) between solvent particle (larger amount). Solute (lesser amount) + Solvent (larger amount) Solution 𝐍𝐚𝐂𝐥(𝐬) + 𝐇𝟐𝐎(𝐥) → 𝐒𝐚𝐥𝐭 𝐒𝐨𝐥𝐮𝐭𝐢𝐨 Concentrated Solution has a large amount of solute. Dilute Solution has a small amount of solute. Classification of solutions according to amount of solute: (1) Unsaturated solutions: if the amount of solute dissolved is less than the solubility limit, or if the amount of solute is less than capacity of solvent. 12  Lecture (3) (2) Saturated solutions: is one in which no more solute can dissolve in a given amount of solvent at a given temperature, or if the amount of solute equal to capacity of solvent. (3) Super saturated solutions: solution that contains a dissolved amount of solute that exceeds the normal solubility limit (saturated solution). Or a solution contains a larger amount of solute than capacity of solvent at high temperature. Classification of solution based on solute particle size: (1) True solution: A homogeneous mixture of two or more substance in which substance (solute) has a particle size less than 1 nm dissolved in solvent. Particles of true solution cannot be filtered through filter paper and are not visible to naked eye (NaCl in water). (2) Suspension solution: heterogeneous mixtures which settles on standing and its components can be separated by filtrating (Amoxcycilline Antibiotics), particle of solute visible to naked eye. (3) Colloidal solution: homogeneous mixture which does not settle nor are their components filterable, solute particle visible with electron microscope (milk). Stoichiometric Calculations:- Gram atomic weight (gAw some time Awt): Is the weight of a specified number of atoms of that element (contains exactly the same number of atoms of that element as there are carbon atoms in exactly 12g of carbon 12 (this number is Avogadro’s number = 6.0221023 atoms). Gram molecular weight (gMw some times M.wt): Defined as the sum of the atomic weight of the atoms that make up a molecular compound. Gram formula weight (gFw some time F.wt): The sum of the atomic weight of the atoms that make up an ionic formula. (is the more accurate description for substances that do not exist as molecules but exist as ionic compounds e.q strong electrolytes-acids, bases, salts). Sometimes use the term molar mass (Molecular weight, M.wt) in place of gram formula weight, gFw). Example (1) :-Calculate the number of grams in one mole of CaSO4.7H2O (calculate gram molecular or formula weight). Solution: One mole is the formula weight expressed in grams. The formula weight is (Ca=40.08; S=32.06; O=16.00; H=1.01) 𝐂𝐚𝐒𝐎𝟒. 𝟕𝐇𝟐𝐎 = 𝟒𝟎. 𝟎𝟖 + 𝟑𝟐. 𝟎𝟔 + (𝟏𝟔. 𝟎 × 𝟒) + 𝟕[(𝟐 × 𝟏. 𝟎𝟏) + 𝟏𝟔. 𝟎𝟎] = 𝟐𝟔𝟐. 𝟐𝟓 𝐠/𝐦𝐨𝐥 Diluting Solutions:- We are often concerned with how much solute is dissolved in a given amount of solution. We will begin our discussion of solution concentration with two related and relative terms: Dilute and concentrated. A dilute solution is one in which there is a relatively small amount of solute dissolved in the solution. A concentrated solution contains a relatively large amount of solute. These two terms do not provide any quantitative information (actual numbers), but they are often useful in comparing solutions in a more 13  Lecture (3) general sense. These terms also do not tell us whether or not the solution is saturated or unsaturated, or whether the solution is "strong" or "weak". These last two terms will have special meanings when we discuss acids and bases, so be careful not to confuse them. STOCK SOLUTIONS It is often necessary to have a solution with a concentration that is very precisely known. Solutions containing a precise mass of solute in a precise volume of solution are called stock (or standard) solutions. To prepare a standard solution, a piece of lab equipment called a volumetric flask should be used. These flasks range in size from 10 mL to 2000 mL and are carefully calibrated to a single volume. On the narrow stem is a calibration mark. The precise mass of solute is dissolved in a bit of the solvent, and this is added to the flask. Then, enough solvent is added to the flask until the level reaches the calibration mark. Often, it is convenient to prepare a series of solutions of known concentrations by first preparing a single stock solution, as described in the previous section. Aliquots (carefully measured volumes) of the stock solution can then be diluted to any desired volume. In other cases, it may be inconvenient to weigh a small mass of sample accurately enough to prepare a small volume of a dilute solution. Each of these situations requires that a solution be diluted to obtain the desired concentration. DILUTIONS OF STOCK (OR STANDARD) SOLUTIONS Imagine we have a salt water solution with a certain concentration. That means we have a certain amount of salt (a certain mass or a certain number of moles) dissolved in a certain volume of solution. Next, we will dilute this solution. This is done by adding more water, not more salt: Before Dilution and After Dilution For example ,we may prepare a dilute HCL solution from concentrated HCL to be used for titration.Or ,we may have a stock standard solution from which we wish to prepare a series of more dilute standards.The millimoles of stock solution taken for dilution will be identical to the millimoles in the final diluted solution. M stock × V stock = M diluted × V diluted 14  Lecture (3) Volumetric analysis (titration analysis):- Volumetric analysis is a general term for a method in quantitative chemical analysis in which the amount of a substance is determined by the measurement of the volume that the substance occupies. It is commonly used to determine the unknown concentration of a known reactant. Volumetric analysis is often referred to as titration. Acid-Base Titration What is the meaning of Titration? Titration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the titrant or titrator, of a known concentration (a standard solution) and volume is used to react with a solution of the analyte or titrant, whose concentration is not known. Using a calibrated burette or chemistry pipetting syringe to add the titrant. * A primary standard solution is a highly purified compound that serve as a reference material in all volumetric titrimetric methods. Important requirements for a primary standard are: 1- High purify. 2. To be of high stability and not affected or interact in one way or another under normal weather conditions. 3. Ready availability at modest cost. 4. Reasonable solubility in the titration medium. 5. Reasonable large molar mass so that the relative error associated with weighing the standard is minimized. It is possible to determine the exact amount that has been consumed when the endpoint is reached. The endpoint is the point at which the titration is complete, as determined by an indicator. This is ideally the same volume as the equivalence point, the volume of added titrant at which the number of moles of titrant is equal to the number of moles of analyte. For example: - in the classic strong acid- strong base titration, the endpoint of a titration is the point at which the pH of the reactant is just about equal to 7, and often when the solution takes on a persisting solid color as in the pink of phenolphthalein indicator. There are however many different types of titrations. 15  Lecture (3) Many methods can be used to indicate the endpoint of a reaction; titrations often use visual indicators (the reactant mixture changes color). In simple acid-base titrations a pH indicator may be used, such as phenolphthalein, which becomes pink when a certain pH (about 8.2) is reached or exceeded. Another example is methyl orange, which is red in acids and yellow in alkali solutions. Not every titration requires an indicator. In some cases, either the reactants or the products are strongly colored and can serve as the "indicator". For example, a redox titration using potassium permanganate (pink/purple) as the titrant does not require an indicator. When the titrant is reduced, it turns colorless. After the equivalence point, there is excess titrant present. The equivalence point is identified from the first faint persisting pink color (due to an excess of permanganate) in the solution being titrated. Types of titrations There are various sorts of titrations whose goals are different to the others. The most common types of titrations in qualitative work are acid-base titrations ,redox titrations, complexometric titration and precipitation titration. 1- Neutralization titrations (Acid-base titration) These titrations are based on the neutralization reaction that occurs between an acid and a base, when mixed in solution. The acid is added to a burette which was rinsed with the same acid prior to this addition to prevent contamination or diluting of the acid being measured. The base is added to a volumetric flask which had been rinsed with distilled water prior to the addition to prevent contamination or dilution of the base/alkali being measured. The solution in the volumetric flask is often a standard solution (one whose concentration is exactly known). The solution in the burette, however, is the solution whose concentration is to be determined by titration. The indicator used for such an acid-base titration often depends on the nature of the constituents. Common indicators, their colours, and the pH range in which they change colour, are given in the table below, when more precise results are required, or when the titration constituents are a weak acid and a weak base, a pH meter or a conductance meter are used. Sq. Indicator Color on Acidic Side Range of Color Color on Basic Side Change (pH) 1 Methyl Violet Yellow 0.0- 1.6 Violet 2 Bromophenol Blue Yellow 3.0- 4.6 Blue 3 Methyl Orange Red 3.1- 4.4 Yellow 4 Methyl Red Red 4.4- 6.2 Yellow 5 Litmus Red 5.0- 8.0 Blue 6 Bromothymol Blue Yellow 6.0- 7.6 Blue 7 Phenolphthalein Colorless 8.3- 10.0 Pink 8 Alizarin Yellow Yellow 10.1- 12.0 Red 𝐂𝐇𝟑𝐂𝐎𝐎𝐇 + 𝐍𝐚𝐎𝐇 → 𝐂𝐇𝟑𝐂𝐎𝐎𝐍𝐚 + 𝐇 16  Lecture (3) 2- Precipitation titration Precipitation titration: is titration depend upon the combination of ions to form a simple precipitate. Mohr method is a method depend upon formation a colored precipitate for the determination of chloride ion. A small quantity of potassium chromate (K2CrO4) solution is added to serve as indicator. The first excess of titrant results in the formation of a red silver chromate precipitate which signal the end point. 3- Redox titration These titrations are based on a redox reaction between an oxidizing agent and a reducing agent. The oxidizing agent is added to the burette which was rinsed with the same oxidizing agent. The reducing agent is added to the conical flask, which had been rinsed with distilled water. Like in an acid-base titration, the standard solution is often the one in the conical flask, and the solution whose concentration is to be determined is the one in the burette. Some redox titrations do not require an indicator, due to the intense colour of some of the constituents. For instance, in a titration where the oxidizing agent potassium permanganate (permanganometry) is present, a slight faint persisting pink colour signals the endpoint of the titration, and no particular indicator is therefore required. 4- Complexometric titration These titrations are based on the formation of a complex between the analyte and the titrant. The chelating agent Ethylenediaminetetraacetic acid (EDTA) is very commonly used to titrate metal ions in solution. These titrations generally require specialized indicators that form weaker complexes with the analyte. A common example is Eriochrome Black T and muroxide for the titration of calcium and magnesium ions. Ethylenediaminetetraacetic acid (EDTA) General Steps of Titrimetric analysis: 1) Sampling 2) Titrant preparation 3) Standard preparation and conversion to a measurable form. 4) Titrant standardization by titration of an accurately known quantity of standard 5) Sample preparation and conversion to a measurable form 6) Sample titration with the titrant solution 7) Data analysis Successful Titrimetric Analysis A few rules of thumb for designing a successful titration are: The titrant should either be a standard or should be standardized. The reaction should proceed to a stable and well-defined equivalence point. 17  Lecture (3) The equivalence point must be able to be detected. The titrant’s and sample’s volume or mass must be accurately known. The reaction must proceed by a definite chemistry. There should be complicating side reactions. The reaction should be nearly complete at the equivalence point. In other words, chemical equilibrium favors products. The reaction rate should be fast enough to be practical. Substances of known purity for the preparation of standard solution. A visual indicator or an instrumental method detecting the completion of the reaction Calibrated measuring vessels, including burettes, pipettes, and measuring flasks as followes:- Calculations of volumetric analysis: Standard solution is one, which contains a known weight of the reagent in a definite volume of the solution. Molar solution is one, which contains 1 gm molecular weight of the reagent per liter of solution. Normal solution is one that contains 1gm equivalent weight per liter of solution. Part per million(ppm): Milligrams of solute per liter of solution. For titrimetric reaction: aA+bB product titrant titrand At equivalent point: no.mmol of titrant(A)= no.mmol of titrand(B) NA × VA = NB × VB Or MA × VA = MB × VB (R=b/a) Equivalent weights (1) Equivalent weight in neutralization reactions. The equivalent weight of acid is that weight of it which contains one-gram atom of replaceable hydrogen. 18  Lecture (3) Ex: equivalent weight of H2SO4 =M.Wt H2SO4/2 equivalent weight of H3PO4 =M.Wt H3PO4/3 The equivalent weight of Base is that weight of it which contains one replaceable hydroxyl group. Ex: equivalent weight of NaOH =M.Wt NaOH/1 2) Equivalent weight in Oxidation -reduction reactions. The equivalent weight of an oxidant or a reductant is the number of electrons which 1moL of the substance gains or losses in the reaction. 3) Equivalent weight of complex formation and precipitation reactions. Here the equivalent weight is the weight of the substance which contains or reacts with 1g. atm of a univalent cation M+. Ex: When silver nitrate reacts with sodium chloride, to form silver chloride, the equivalent weight of AgNO3 is: 19  Lecture (4) Acid-Base Equilibria Acid-base theories:- 1) Arrhenius Theory (H+ and OH- ): Acid:-any substance that ionizes (partially or completely) in water to give hydrogen ion (which associate with the solvent to give hydronium ion H3O + ): 𝐇𝐀 + 𝐇𝟐𝐎 ↔ 𝐇𝟑𝐎 + + 𝐀 – Base:-any substance that ionizes in water to give hydroxyl ions. Weak (partially ionized) to generally ionize as follows:- 𝐁 + 𝐇𝟐𝐎 ↔ 𝐁𝐇+ − 𝐎𝐇− While strong bases such as metal hydroxides (e.g. NaOH) dissociate as 𝐌(𝐎𝐇)𝐧 ↔ 𝐌𝐧+ + 𝐧𝐎𝐇− This theory is obviously restricted to water as the solvent. 2) Bronsted-Lowry Theory (taking and giving protons, H+ ):- Acid:-any substance that can donate a proton. Base:-any substance that can accept a proton. Thus, we can write a half reaction: Acid = H+ + Base 3) Lewis Theory (taking and giving electrons):- Acid:-a substance that can accept an electron pair. Base:-a substance that can donate an electron pair. Pure water ionizes slightly, or undergoes autoprotolysis (self-ionization of solvent to give a cation and anion):- 𝟐𝐇𝟐𝐎 ↔ 𝐇𝟑𝐎 + + 𝐎𝐇− 20 Lecture (4) 21