Volumetric Analysis Titration Dr.Riham Hazzaa

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. Dr.Riham Hazzaa

Standard solution is a chemical term which describes a solution of known concentration. Primary Standard: Substances whose exact solution concenteration can be determined by transferring a known weight of the reagent to a volumetric flask and diluting to the mark with solvent Secondary standard: A titrant is prepared in an approximate concentration and then titrated against a primary standard to determine its exact concenteration Standardization process of calibrating the secondary standard against our primary standard Dr.Riham Hazzaa

M = Amount of moles of solute liters of solution Molarity: is defined as the number of moles of solute divided by the number of liters of solution containing the solute. M = Amount of moles of solute liters of solution Amount of moles of solute = Weight MW Dr.Riham Hazzaa

N = Amount of equivalent(eq) of solute Liters of solution Normality: is defined as the number of equivalents (eq) of solute divded by the number of liters of solution containing the solute. N = Amount of equivalent(eq) of solute Liters of solution Amount of equivalents (eq) = weight (grams) EW Equivalent weight= Molecular weight Z Dr.Riham Hazzaa

Normality is related to molarity: M = Weight OR MW = Weight MW×volume M×volume N = Weight OR EW = Weight EW×volume N×volume Equivalent weight = Molecular weight Z Weight × Z = Weight N×volume M ×volume Thus, Normality (N) = Molarity (M)  (Z) Dr.Riham Hazzaa

Normality is related to molarity: Normality (N) = Molarity (M)  (Z) 1M sulfuric acid H2SO4 is 2N for acid-base reactions because each mole of sulfuric acid provides 2 moles of H+ ions (Z). Dr.Riham Hazzaa

After Dilution Before Dilution moles1 = moles2 Solution1 Solution2 M1 = moles1 litre1 M2 = moles2 litre2 moles1 = moles2 M1 × litre1 = M2 × litre2 Dr.Riham Hazzaa

Acids and Bases Titration

Properties of Acids An acid is any substance that releases hydrogen ions, H+, into water. Blue litmus paper turns red in the presence of hydrogen ions. Blue litmus is used to test for acids. Acids have a sour taste; lemons, limes, and vinegar are acidic. Dr.Riham Hazzaa

Properties of Bases A base is a substance that releases hydroxide ions, OH –, into water. Red litmus paper turns blue in the presence of hydroxide ions. Red litmus is used to test for bases. Bases also have a bitter taste; soapy feel. Dr.Riham Hazzaa

Neutralization Reactions If we have an acid with two hydrogens (sulfuric acid, H2SO4), we need two hydroxide ions to neutralize it. H2SO4(aq) + 2 NaOH(aq) → Na2SO4(aq) + 2 H2O(l) H2SO4(aq) + Ca(OH)2(aq) → CaSO4(aq) + 2 H2O(l) Dr.Riham Hazzaa

Acid-Base Reactions with Gas Formation 1. Carbonates react with acids to form CO2, carbon dioxide gas. NaCO3+ 2HCl → 2NaCl + H2O +CO2 2. Sulfites react with acids to form SO2, sulfur dioxide gas. Na2SO3 2HCl → 2NaCl + H2O + SO2 3. Sulfides react with acids to form H2S, hydrogen sulfide gas. Na2S + 2HCl → 2NaCl + H2S Dr.Riham Hazzaa

Acid/Base Neutralization An acid and a base react with each other in a neutralization reaction. When an acid and a base react, water and a salt are produced. For example, nitric acid reacts with sodium hydroxide to produce sodium nitrate and water: HNO3(aq) + NaOH(aq) → NaNO3(aq) + H2O(l) Dr.Riham Hazzaa

[H+] is the molar hydrogen ion concentration The pH Scale A pH value expresses the acidity or basicity of a solution. Most solutions have a pH between 0 and 14. Acidic solutions have a pH less than 7. As a solution becomes more acidic, the pH decreases. Basic solutions have a pH greater than 7. As a solution becomes more basic, the pH increases. pH = –log[H+] [H+] = 10–pH [H+] is the molar hydrogen ion concentration

Acid/Base Classifications of Solutions Strongly acidic solutions have a pH less than 2. Weakly acidic solutions have a pH between 2 and 7. Weakly basic solutions have a pH between 7 and 12. Strongly basic solutions have a pH greater than 12. Neutral solutions have a pH of 7. Dr.Riham Hazzaa

Acid – base theories 1. Arrhenius theory 2. The Brønsted –Lowry theory 3. Lewis theory Dr.Riham Hazzaa

Arrhenius Theory Svante Arrhenius proposed the following definitions for acids and bases in 1884: An Arrhenius acid is a substance that ionizes in water to produce hydrogen ions. An Arrhenius base is a substance that ionizes in water to release hydroxide ions. For example: HCl is an Arrhenius acid NaOH is an Arrhenius base. Dr.Riham Hazzaa

Strengths of Acids Acids have varying strengths. The strength of an Arrhenius acid is measured by the degree of ionization in solution. Ionization is the process where polar compounds separate into cations and anions in solution. The acid HCl ionizes into H+ and Cl– ions in solution. HCl + H2O → H3O+ + Cl- hydronium ions Dr.Riham Hazzaa

Arrhenius Acids in Solution All Arrhenius acids have a hydrogen atom bonded to the rest of the molecule by a polar bond. This bond is broken when the acid ionizes. Polar water molecules help ionize the acid by pulling the hydrogen atom away: HCl(aq) + H2O(l) → H3O+(aq) + Cl–(aq) (~100%) HC2H3O2(aq) + H2O(l) → H3O+(aq) + C2H3O2–(aq) (~1%) The hydronium ion, H3O+, is formed when the aqueous hydrogen ion attaches to a water molecule. Dr.Riham Hazzaa

Strong & Weak Arrhenius Acids Strong acids ionize extensively (completly) to release hydrogen ions into solution. HCl is a strong acid and ionizes nearly 100% Weak acids only ionize slightly(partialy )in solution. HF is a weak acid and ionizes only about 1%

Strengths of Bases Bases also have varying strengths. The strength of an Arrhenius base is measured by the degree of dissociation in solution. Dissociation is the process where cations and anions in an ionic compound separate in solution. A formula unit of NaOH dissociates into Na+ and OH– ions in solution. NaOH  Na+ + OH- Dr.Riham Hazzaa

Arrhenius Bases in Solution When we dissolve Arrhenius bases in solution, they dissociate giving a cation and a hydroxide anion. Strong bases dissociate almost fully and weak bases dissociate very little: NaOH(aq) → Na+(aq) + OH–(aq) (~100%) NH4OH(aq) ↔ NH4+(aq) + OH–(aq) (~1%) Dr.Riham Hazzaa

Strong & Weak Arrhenius Bases Strong bases dissociate extensively to release hydroxide ions into solution. NaOH is a strong base and dissociates nearly 100% Weak bases only ionize slightly in solution. NH4OH is a weak base and only partially dissociates

Brønsted-Lowry Theory The Brønsted-Lowry definitions of acids and bases are broader than the Arrhenius definitions. A Brønsted-Lowry acid is a substance that donates a hydrogen ion to any other substance. It is a proton donor. A Brønsted-Lowry base is a substance that accepts a hydrogen ion. It is a proton acceptor. Dr.Riham Hazzaa

Brønsted-Lowry Acids & Bases Lets look at two acid/base reactions: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) HCl(aq) + NH3(aq) → NH4Cl(aq) HCl donates a proton in both reactions and is a Brønsted-Lowry acid. In the first reaction, the NaOH accepts a proton and is the Brønsted-Lowry base. In the second reaction, NH3 accepts a proton and is the Brønsted-Lowry base. Dr.Riham Hazzaa

Amphiprotic Compounds A substance that is capable of both donating and accepting a proton is an amphiprotic compound. NaHCO3 is an example: HCl(aq) + NaHCO3(aq) → NaCl(aq) + H2CO3(aq) NaOH(aq) + NaHCO3(aq) → Na2CO3 (aq) + H2O(l) NaHCO3 accepts a proton from HCl in the first reaction and donates a proton to NaOH in the second reaction. Dr.Riham Hazzaa

Dr.Riham Hazzaa

H+ + :NH3  H:NH3+ Lewis Theory Lewis acid-base theory relates acid-base behavior of molecules to their molecular structure. Lewis acid- A species that is an electron pair acceptor. Lewis base- A species that is an electron pair donor. H+ + :NH3  H:NH3+ Dr.Riham Hazzaa

Acid-Base Titrations A titration is used to analyze an acid solution using a solution of a base. A measured volume of base is added to the acid solution. When all of the acid has been neutralized, the pH is 7. One extra drop of base solution after the endpoint increases the pH dramatically. When the pH increases above 7, phenolphthalein changes from colorless to pink indicating the endpoint of the titration. Dr.Riham Hazzaa

Acid-Base Indicators Methyl Red Bromothymol Blue Phenolphthalein Dr.Riham Hazzaa

Acid-Base Titrations: Strong Acid/Strong Base HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) ? M KNOWN M Dr.Riham Hazzaa

Titration curve 30/09/99 7 14 25 50 Fewer moles of H2SO4 would be required to neutralize 25 mL NaOH, thus the curve would shift left 7 14 25 50 Because we start with pure HCl, then add NaOH the pH starts low then goes high, thus the curve flips Dr.Riham Hazzaa

The theory Begin with a balanced equation for the reaction: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) na = 1 nb = 1 (mole ratios of acid and base) Mole = concentration X volume For the acid: na = MaVa For the base: nb = MbVb na : nb (stoichiometry mole ratio) MaVa : MbVb Dr.Riham Hazzaa

The Theory na : nb MaVa : MbVb i.e. na nb MaVa MbVb Then, MaVa na MbVb nb = = MaVa na MbVb nb = Dr.Riham Hazzaa

Titration Problem 1.What is the molarity of a hydrochloric acid solution if 25.50 mL are required to neutralize 0.375 g Na2CO3? 2 HCl(aq) + Na2CO3(aq) → 2 NaCl(aq) + H2O(l) + CO2(g) = 0.277 M HCl the molarity of a hydrochloric acid 2. A 10.0 mL sample of 0.555 M H2SO4 is titrated with 0.233 M NaOH. What volume of NaOH is required for the titration? H2SO4(aq) + 2 NaOH(aq) → Na2SO4(aq) + H2O(l) volume of NaOH = 49.8 mL NaOH Dr.Riham Hazzaa