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Volumetric Analysis

ANALYTICAL CHEMISTRY. Volumetric Analysis. Chapter 4. Dr. salwa albohy. Volumetric Analysis. Volumetric Analysis : depends on interaction of substances in solution in the ratio of their equivalent weights . Volumetric analysis involves using volumes of liquids to analyse a concentration.

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Volumetric Analysis

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  1. ANALYTICAL CHEMISTRY Volumetric Analysis Chapter 4 Dr. salwaalbohy lecture3

  2. Volumetric Analysis Volumetric Analysis : depends on interaction of substances in solution in the ratio of their equivalent weights . Volumetric analysisinvolves using volumes of liquids to analyse a concentration lecture3

  3. Volumetric Analysis concentration-What equation do we know involving n = Cv -Concentration is expressed in mol L-1, which is given the symbol M (C). To do this we need the following things: I.A chemical of a known concentration that will react with our ‘unknown’ concentration chemical II. An indicator that will tell us when all the chemical has been reacted lecture3

  4. Volumetric analysis To understand volumetric analysis, we must understand the types of reaction that happen in it. Types of reactions used in volumetric analysis : I- Ionic combination reactions:- - The reaction goes to completion due to formation of slightly ionizable or slightly insoluble products. a- Neutralization reaction : In which acid reacts with base to form slightly ionized water. H+ + OH- H2O b- Formation of precipitate : Ag+ + Cl- AgCl  c- Formation of slightly ionizable complex : Ag+ + 2 CN- [Ag(CN)2]- Ca+2 + H2Y-2 [EDTA] 2H+ + CaY-2 [Ca-EDTA complex] • II- Electron transfer reactions : • In which electron transfer from one reactant to another. It is called • (oxidation -reduction reactions) Ce+4 + Fe+2 Ce+3 + Fe+3 i.e. Fe+2 Fe+3 + e oxidation (loss of es.) Ce+4 + e Ce+3 reduction (gain of es)

  5. Volumetric Analysis Classification of Volumetric Methods 1. Acid-base titrations. 2. Precipitation titrations. 3. Complexometric titrations. 4. Reduction-oxidation (Redox) titrations lecture3

  6. Titrations In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete.مهم Equivalence point – the point at which the reaction is complete Indicator – substance that changes color as the pH of a solution changes (or near) the equivalence point Slowly add base to unknown acid UNTIL the indicator changes color lecture3

  7. Acids and Bases lecture3

  8. Acid–Base Learning Objectives • To know that solutions can be sorted by whether they are: acid, Baseor neutral. lecture3

  9. Acid Properties sour taste change the color of litmus from blue to red. react with * metals such as zinc and magnesium to produce hydrogen gas * bases to produce water and an ionic compound (salt) * carbonates to produce carbon dioxide. .. These properties are due to the release of hydrogen ions, H+, into water solution. lecture3

  10. Acids There are many acids present in our everyday lives. Lemon juice contains citric acid, and vinegar contains acetic acid. Some strong acids are hydrochloric acid, sulphuric acid and nitric acid. Some weak acids are ethanoic acid, citric acid and carbonic acid. lecture3

  11. Base Properties *bitter or caustic taste * a slippery, soapy feeling. * the ability to interact with acids * the ability to change litmus red to blue These properties are due to the release of hydroxide ions, OH-, into water solution. lecture3

  12. Bases Bases are present in many cleaning substances in use in our homes Kitchen cleaners are alkaline because they contain ammonia or sodium hydroxide, which attack grease. lecture3

  13. Acid-Base Acid- base theories 1- Arrhenius theory :- Acid : Is the substance which ionize to give H+ eg. HCl Base : Is the substance which ionize to give OH- eg NaOH 2- Bronsted - Lowry theory :- Acid : Is the substance which donate proton. Base : Is the substance which accept proton. Every acid has a conjugate base and the base has conjugate acid. The stronger the acid the weaker its conjugate base and vice versa. Eg. HCl + H2O Cl- + H3O+ Acid base conj.base conj.acid Eg. NH3 + H2O NH4+ + OH- base acid conj.acid conj.base N.B. Water behave as acid or base because it is neutral.

  14. 3- Lewis theory :- Acid : Is substance which accept lone pair of electrons eg. BF3, AlCl3. Base : Is substance which donate lone pair of electrons eg NH3, amines.

  15. 1.Arrhenius acid and base Arrhenius acid is a substance that produces H+ (H3O+) in water Arrhenius base is a substance that produces OH- in water lecture3

  16. Hydronium ion, hydrated proton, H3O+ lecture3

  17. 2. Brønsted acid and base A Brønsted acid must contain at least one ionizable proton! A Brønsted acid is a proton donor A Brønsted base is a proton acceptor base acid acid base lecture3

  18. Brønsted acid and base Ammonia acts as a weak Brønsted base ( proton acceptor)and water acts as an acid (proton donor) base acid acid base lecture3

  19. Water acts as a weak Brønsted base ( proton acceptor) and HCl acts as an acid (proton donor) Brønsted acid and base lecture3

  20. Water acts as an base or as acid depends on the other species present. Brønsted acid and base lecture3

  21. Brønsted acid and base HI (aq) H+ (aq) + I- (aq) CH3COO- (aq) + H+ (aq) CH3COOH (aq) H2PO4- (aq) H+ (aq) + HPO42- (aq) H2PO4- (aq) + H+ (aq) H3PO4 (aq) Identify each of the following species as a Brønsted acid, base, or both. (a) HI, (b) CH3COO-, (c) H2PO4- Brønsted acid Brønsted base Brønsted acid Brønsted base lecture3

  22. Acids and Bases lecture3

  23. acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H2O H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O H+ + OH- H2O Acid–Base reactions Acid–Base reactions = Neutralization reactions lecture3

  24. Acid-Base Titrations An acid-base titration can be used to determine the concentration of an acid or base solution titration: a technique for determining the concentration of an unknown solution using a standard solution a solution with a known concentration lecture3

  25. Acid-Base Titrations The equivalence point in a titration can be determined using either a pH indicator (ex. Phenolphthalein ph.ph) or a pH meter. Equivalence point: the point in the titration where stoichiometrically equivalent amounts of base have been added to the acid (or vice versa) the base added has completely reacted with all available protons (H+) lecture3

  26. Equivalence point Region of high buffer capacity pKa Acid-Base Titrations The general shape for a titration curve for a monoprotic acid: pH mL base added lecture3

  27. lecture3

  28. pH is the negative logarithm of the hydrogen ion concentration. pH Scale pH = -log [H+] Similar definition is made for the [OH-]: P OH = - log [OH-] lecture3

  29. pH [H+]= 10-1M pH = – log [H+] Log scale means 10X change per unit! [H+]= 10-9 M lecture3

  30. pH Scale • pKw = pH + pOH at 25oC 14 = pH + pOH • [H+] = [OH-]  the solution is neutral (pH=7). • [H+]  [OH-]  the solution is acidic (pH 7). • [H+]  [OH-]  the solution is alkaline (pH 7). lecture3

  31. pH Scale lecture3

  32. pH Scale Measures the degree of acidity (0 – 14) Most biologic fluids are in the pH range from 6 – 8 A small change in pH actually indicates a substantial change in H+ and OH- concentrations. lecture3

  33. A substance that eliminates large sudden changes in pH. Buffers help organisms maintain the pH of body fluids within the narrow range necessary for life. Are combinations of H+ acceptors and donors forms in a solution of weak acids or bases Work by accepting H+ from solutions when they are in excess and by donating H+ when they have been depleted. Buffers lecture3

  34. Buffers A pH buffer is a solution that resists changes in pH A pH buffer contains a weak acid (HA) and its conjugate base (A-); or a weak base (A-) and its conjugate acid. If a strong base (OH-) is added to a buffered solution, the weak acid in the buffer (HA) will react with OH- to give H2O and the weak base (A-). This results in converting a strong base (OH-) into a weak base (A-). As a result, the pH will slightly increase. HA + OH-➔ H2O + A- If a strong acid acid (H+) is added to a buffered solution, the weak base in the buffer (A-) will react with the (H+) ion to give HA. This results in converting a strong acid H+ into a weak acid HA. As a result, the pH will slightly decrease. A- + H+ ➔ HA

  35.  The main buffer system of the human blood is A.H2CO3 - HCO3 B.H2CO3 - CO32- C.CH3COOH - CH3COO- D.NH2CONH2 - NH2CONH+ lecture3

  36. In this system, carbon dioxide (CO2) combines with water to form carbonic acid (H2CO3), which in turn rapidly dissociates to form hydrogen ions and bicarbonate (HCO3- ). The carbon dioxide - carbonic acid equilibrium is catalyzed by the enzyme carbonic anhydrase; the carbonic acid - bicarbonate equilibrium is simple proton dissociation/association and needs no catalyst lecture3

  37.  Which among the following acids is abundant in Grapes, Bananas and Tamarind?[A]Lactic Acid[B]Oxalic Acid[C]Salicylic Acid[D]Tartaric Acid lecture3

  38. Thank you lecture3

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