Acid-Base Chemistry Quiz
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Questions and Answers

What ions do bases produce when they ionize in water?

  • Oxygen ions (O2-)
  • Hydronium ions (H3O+)
  • Hydroxyl ions (OH-) (correct)
  • Hydrogen ions (H+)

    • Which of the following is a noted shortcoming of the definition of bases?

  • It does not describe their physical properties
  • It includes all non-metal oxides
  • It lacks explanation of acids and bases in non-aqueous media (correct)
  • It requires a presence of water

    • Which option does NOT describe a property associated with bases?

  • They turn litmus paper red (correct)
  • They can ionize to produce hydroxyl ions
  • They taste bitter
  • They feel slippery

    • In aqueous solutions, what is the result of base ionization?

    <p>Production of hydroxyl ions (OH-) (B)</p> Signup and view all the answers

    Why is the study of acid-base equilibria in non-aqueous media important?

    <p>It helps understand chemical reactions in different solvents (D)</p> Signup and view all the answers

    What will be the hydrogen ion concentration in a solution of salts derived from strong acids and bases in pure water?

    <p>$1 imes 10^{-7}$ M (B)</p> Signup and view all the answers

    Which ions do not react with water according to the information provided?

    <p>K+ (B), Cl- (C)</p> Signup and view all the answers

    What pH value corresponds to the hydrogen ion concentration of $1 imes 10^{-7}$ M?

    <p>pH = 7 (B)</p> Signup and view all the answers

    In solutions containing strong acids and bases, where does the hydrogen ion concentration primarily originate?

    <p>From water dissociation (A)</p> Signup and view all the answers

    Which of the following statements is true regarding K+ and Cl- ions in water?

    <p>They do not react with water. (C)</p> Signup and view all the answers

    What is the primary reaction in the Mohr Method for determining Cl- concentration?

    <p>Ag+(aq) + Cl-(aq)  AgCl(s) (C)</p> Signup and view all the answers

    In the Volhard Method, what forms as a result of the reaction between excess Ag+ and SCN-?

    <p>AgSCN(s) (B)</p> Signup and view all the answers

    Which statement about Fajans Titration is correct?

    <p>An adsorption indicator is used in the process. (D)</p> Signup and view all the answers

    What color does dichlorofluorescein exhibit when absorbed on AgCl during Fajans Titration?

    <p>Pink (B)</p> Signup and view all the answers

    In the Volhard Method, what is the role of Fe3+?

    <p>It acts as an indicator forming a red complex. (A)</p> Signup and view all the answers

    What type of ligand is EDTA classified as?

    <p>Hexadentate ligand (D)</p> Signup and view all the answers

    Which of the following statements about the formation constants of EDTA complexes is true?

    <p>Log KMY values can help assess the stability of metal ion complexes. (D)</p> Signup and view all the answers

    How many acid dissociation steps does EDTA have?

    <p>4 (C)</p> Signup and view all the answers

    Which of the following metals forms the most stable complex with EDTA based on its log KMY value?

    <p>Fe3+ (B)</p> Signup and view all the answers

    What does the term 'a4' refer to in the context of EDTA complex formation?

    <p>The ratio of Y4- to total concentration of EDTA (B)</p> Signup and view all the answers

    Which reaction demonstrates the combination of EDTA with a metal ion?

    <p>Ag+ + Y4- ⇌ AgY3- (D)</p> Signup and view all the answers

    What happens to the concentration of Y4- as pH decreases?

    <p>Y4- concentration decreases (A)</p> Signup and view all the answers

    Which of the following is NOT a form of EDTA?

    <p>Y5- (A)</p> Signup and view all the answers

    What is the concentration of hydroxide ions, [OH-], after adding 1.00 mL of 0.1000M HCl to 100.0 mL of 0.1000M NaOH?

    <p>0.09802M (D)</p> Signup and view all the answers

    What is the pH of the solution after the addition of 1.00 mL of 0.1000M HCl to 100.0 mL of 0.1000M NaOH?

    <p>12.9913 (B)</p> Signup and view all the answers

    How do you calculate the concentration of hydronium ions, [H3O+], in the solution?

    <p>[H3O+] = Kw / [OH-] (A)</p> Signup and view all the answers

    Which equation best represents the calculation of [OH-] in the given context?

    <p>[OH-] = (CbVb - CaVa) / (Vb + Va) (C)</p> Signup and view all the answers

    What is the role of Kw in calculating [H3O+]?

    <p>It is the product of concentrations of H+ and OH- at any temperature. (A)</p> Signup and view all the answers

    At the midpoint of a titration of a weak acid with a strong base, what is the relationship between pH and pKa?

    <p>pH = pKa (C)</p> Signup and view all the answers

    What is the initial pH of a 0.1M acetic acid solution before any titration is performed?

    <p>2.8785 (B)</p> Signup and view all the answers

    In a titration of 50.0 mL of 0.1 M HOAc with 10.0 mL of NaOH, what is the concentration of acetate ion (OAc-) after this addition?

    <p>0.0167 M (C)</p> Signup and view all the answers

    Which expression correctly describes [H3O+] during the buffer region of the titration?

    <p>[H3O+] = (Ka * [HOAc]) / [OAc-] (A)</p> Signup and view all the answers

    At the equivalence point of the titration, how does the pH compared to 7?

    <p>pH &gt; 7, basic (A)</p> Signup and view all the answers

    What is the formula to calculate the concentration of OAc- at the equivalence point?

    <p>Cs = CbVb / (Va + Vb) (B)</p> Signup and view all the answers

    What determines the pH after the equivalence point in the titration of acetic acid with sodium hydroxide?

    <p>The concentration of excess NaOH (A)</p> Signup and view all the answers

    What can be concluded about the concentration of OAc- at the half-neutralization point?

    <p>It is equal to 0.05 M (B)</p> Signup and view all the answers

    Flashcards

    Base

    A substance that produces hydroxide ions (OH-) when dissolved in water.

    Base in non-aqueous media

    The ability of a substance to act as a base can vary depending on the solvent it is dissolved in.

    Acid

    Substances that donate hydrogen ions (H+) when dissolved in water.

    Aqueous Solution Equilibria

    The study of chemical reactions and equilibrium involving substances dissolved in water.

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    Equilibrium

    The balance between the forward and reverse reactions in a chemical reaction.

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    Water dissociation

    The process where water molecules spontaneously split into hydrogen ions (H+) and hydroxide ions (OH-) in equal amounts.

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    Hydrogen ion concentration in strong acid/base salt solutions

    In solutions of salts formed from strong acids and strong bases, the hydrogen ion concentration is solely determined by the dissociation of water molecules.

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    Hydrogen ion concentration in pure water

    The concentration of hydrogen ions (H+) in pure water is 10^-7 M at 25°C.

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    pH

    A measure of the acidity or alkalinity of a solution. It is the negative logarithm of the hydrogen ion concentration (pH = -log[H+]).

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    K+ and Cl- interaction with water

    Neither potassium ions (K+) nor chloride ions (Cl-) react with water to alter its hydrogen ion concentration.

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    Equivalence Point

    The point in a titration where the moles of acid and base are equal, resulting in complete neutralization.

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    pH at Equivalence Point: Strong Acid & Strong Base

    The pH at the equivalence point depends on the strength of the acid and base. For the reaction of a strong acid and strong base, the pH at the equivalence point is 7.00.

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    pH at Equivalence Point: Weak Acid & Strong Base

    The pH at the equivalence point for a titration involving a weak acid and strong base will be greater than 7.00 due to the formation of the conjugate base of the weak acid.

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    pH at Equivalence Point: Strong Acid & Weak Base

    The pH at the equivalence point for a titration involving a strong acid and weak base will be less than 7.00 due to the formation of the conjugate acid of the weak base.

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    Titration Curve

    A graphical representation of the pH of a solution as a function of the volume of titrant added during a titration.

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    Buffer Solution

    A solution containing a weak acid and its conjugate base, or a weak base and its conjugate acid. Buffers resist changes in pH upon addition of small amounts of acid or base.

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    Buffer Region

    The region of a titration curve where the pH changes gradually as the titrant is added. This occurs when the weak acid and its conjugate base (or weak base and its conjugate acid) are present in significant amounts.

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    Titration

    The quantitative analysis of the concentration of an analyte in a solution by reacting it with a solution of known concentration (titrant). The reaction is typically carried out until the equivalence point is reached, which can be determined using an indicator.

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    Indicator

    A substance that changes color in response to a change in pH, indicating the endpoint of a titration. The endpoint ideally coincides with the equivalence point.

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    pH at Equivalence Point

    The pH at the equivalence point is not 7 for the titration of a weak acid and strong base. It is greater than 7 because the conjugate base of the weak acid is a weak base, and it hydrolyzes water slightly to produce OH- ions, thus making the solution slightly basic.

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    Henderson-Hasselbalch Equation

    The pH of a solution of a weak acid can be calculated using the Henderson-Hasselbalch equation, which relates the pH, pKa, and the concentrations of the weak acid and its conjugate base. This equation is particularly useful for calculating the pH of buffer solutions.

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    Mohr Method

    A titration method that uses the difference in solubility between two silver salts, AgCl and Ag2CrO4, to determine the chloride ion concentration. AgCl precipitates first due to its lower solubility, and the endpoint is indicated by the formation of a brick-red precipitate of Ag2CrO4.

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    Volhard Method

    An indirect method used to determine the concentration of silver ions (Ag+) or chloride ions (Cl-) by back titration. Excess silver nitrate (AgNO3) is added to precipitate chloride ions. The remaining silver ions are then titrated with potassium thiocyanate (KSCN) in the presence of iron(III) indicator. The endpoint is reached when a red complex (FeSCN2+) is formed, signaling the complete consumption of silver ions.

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    Fajans Titration

    A method for determining the endpoint of a precipitation titration by using adsorption indicators. These indicators are organic dyes that adsorb onto the surface of the precipitate, leading to a color change at the equivalence point. For instance, dichlorofluorescein adsorbs onto silver chloride (AgCl), changing from green to pink at the equivalence point.

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    Fajans Endpoint

    In the Fajans titration, prior to the equivalence point, there is an excess of chloride ions (Cl-) in solution. This excess Cl- will be adsorbed onto the surface of the AgCl precipitate. The adsorption of Cl- results in a negative charge on the surface of the precipitate, which attracts the positively charged indicator ions. As the titration progresses, the concentration of Cl- decreases, leading to a decrease in the adsorption of Cl- ions and a decrease in the indicator adsorption, thus signaling the endpoint.

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    Mohr Method: Endpoint Detection

    This technique relies on the difference in solubility between two silver salts. AgCl precipitates first due to its lower solubility. The endpoint is indicated by the formation of a brick-red Ag2CrO4 precipitate.

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    EDTA (Ethylenediaminetetraacetic acid)

    A chemical compound that forms stable complexes with metal ions. It has six binding sites (hexadentate) and is commonly used in analytical chemistry, for example, to determine water hardness.

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    Complex Formation

    A chemical reaction where a metal ion and a ligand (like EDTA) combine to form a stable complex.

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    Formation Constant (KMY)

    The strength of a complex is measured by its formation constant, also known as stability constant (KMY). A higher KMY indicates a more stable complex.

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    Fully Deprotonated Form of EDTA (Y4-)

    The pH-dependent form of EDTA that binds to metal ions most effectively. To calculate it, you consider all possible protonated and deprotonated forms of EDTA.

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    Alpha4 (α4)

    A factor that accounts for the pH-dependence of EDTA's ability to bind metal ions. It tells you the fraction of EDTA in its most reactive form (Y4-) at a specific pH.

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    Conditional Formation Constant (KMY')

    The effective formation constant for a metal-EDTA complex at a specific pH. It considers the pH-dependent availability of the fully deprotonated form of EDTA (Y4-) and the overall stability constant (KMY)

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    Solution Chemistry of EDTA

    The study of the equilibrium between different forms of a substance in solution, including the interaction of metal ions with ligands like EDTA.

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    Total EDTA Concentration (CT)

    The concentration of the total EDTA in solution, considering all possible protonated and deprotonated forms. It's used when calculating the conditional formation constant (KMY').

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    Study Notes

    Acid-Base Equilibria

    • ILOs: Students will learn to calculate pH, evaluate pH values of salts, use the Henderson-Hasselbalch equation, understand buffering capacity, explain polyprotic drugs, calculate pH of solutions with polyprotic species, and construct fractions of polyprotic species as functions of pH.

    Drug Nature and pKa Values

    • Acetyl salicylic acid is an acid with a pKa of 3.49.
    • Benzyl penicillin is an acid with a pKa of 2.76.
    • Ethosunamide is an acid with a pKa of 9.3.
    • Chlorpropamide is an acid with a pKa of 4.8.
    • Sulfadrazine is an acid with a pKa of 6.48.
    • Dephenghydantoin is an acid with a pKa of 8.3.
    • Atropine is a base with a pKa of 9.65.
    • Amphetamine is a base with a pKa of 9.8.
    • Lignocaine is a base with a pKa of 7.9.
    • Procaine is a base with a pKa of 8.8.
    • Tetracycline is a base with pKa values of 3.3, 7.8, and 9.7.

    Acidic Drug Examples

    • Ibuprofen
    • Naproxen
    • Aspirin
    • Nicotinic acid

    Amine-Containing Drugs

    • Labetalol (Trandate)
    • Clobenzorex (Dinintel)
    • Vyvanse (Lisdexamfetamine)
    • Exelon (Rivastigmine)
    • Sensipor (Cinacalcet)
    • Glucagon receptor antagonist (MK-0893)

    Aqueous Solution Equilibria

    • Electrolytes form ions in solution
      • Strong electrolytes are mostly in ionic form
      • Weak electrolytes are mostly not in ionic form
    • Water, methanol, and ethanol are amphiprotic solvents, exhibiting both acidic and basic properties.
    • H2CO3, CH3COOH, and NH3 are amphiprotic solutes
    • Water (2H2O ⇌ H3O+ + OH-) is an amphoteric substance
    • Methanol is an amphoteric substance
    • Glacial acetic acid is an amphoteric substance
      • Some aqueous solutes exhibit both acidic and basic properties

    Acid-Base Theories

    • Arrhenius theory defines acids as substances ionizing in water to release H+ and bases as substances ionizing to release OH-
    • Brønsted-Lowry theory defines acids as proton donors and bases as proton acceptors.

    pH Scale

    • pH = -log[H+]
    • pAnything = -log(Anything)
    • pKw = -logKw at 25°C = 14.00
    • Kw = [H+][OH-]
    • pKw = pH + pOH = 14
    • Blood pH at body temperature (37°C) is typically 7.35-7.45 (slightly basic)

    pH Scale Examples

    • pH of 1M HCl = 0
    • pH of pure water = 7
    • pH of blood = 7.35-7.45
    • pH of 1M NaOH = 14

    Salts of Strong Acids and Bases

    • The pH of the solutions stays constant at 7
    • Ions like Cl- or Na+ do not react significantly with water, keeping the solution neutral

    Weak Acids and Bases

    • Weak acids/bases are partially dissociated in water.
    • The amount dissociated is negligible compared to the original concentration.

    Buffers

    • Buffers resist pH changes upon addition of acid or base.
    • A buffer solution contains a mixture of a weak acid and its conjugate base.
    • Optimal buffering occurs where pH = pKa
    • Buffering capacity = maximum at pH = pKa

    Henderson-Hasselbalch Equation

    • pH = pKa + log [conjugate base]/[acid]

    Polyprotic Acids and Their Salts

    • Polyprotic acids can donate more than one proton, e.g., H3PO4
    • The stepwise dissociation constants for polyprotic acids progressively decrease.

    Titration Curves

    • Titrations are used to determine the concentration of an unknown analyte in a solution
    • Titration curves graph pH vs volume of titrant.
    • The equivalence point is the point at which the titration reaches neutralization
    • Indicators are substances that change color at specific pH ranges, or "equivalence point"

    Acid-Base Color Indicators

    • Organic weak acids/bases that change color over a specific pH range
    • Color change from acid to base form is apparent
    • A high [HIn]/[In-] ratio correlates with color A, while a low [HIn]/[In-] ratio correlates with color B

    Phenolphthalein

    • Weak acid that is colorless in its unionized form, and pink in its ionized form
    • Color change is usually found at pH range 8.2−10.0

    Amino Acids

    • Amino acids are polyprotic
    • Zwitterions are structures with both positive and negative sites.
    • The pI (isoelectric point) is the pH at which the amino acid has a net zero charge.

    Complex Formation Titrations

    • Metal ions form coordination compounds with electron-pair donors (ligands)
    • The coordination number is the number of covalent bonds formed.
    • Chelating ligands (especially multidentate ligands) are preferred for titrations because they form more complete complexes with metal ions

    Chelating Agents

    • Nitrilotriacetic acid (NTA)
    • Ethylenediaminetetraacetic acid (EDTA)
    • Diethylenetriaminepentaacetic acid (DTPA)
    • Trans-1,2-diaminocyclohexanetetraacetic acid (DCTA)
    • Bis-(aminoethyl)glycolether-N,N,N',N'-tetraacetic acid (EGTA)

    EDTA

    • Forms 1:1 complexes with metal ions via 6 ligands (4 O and 2 N)
    • Frequently used in titrations due to its ability to form stable chelates with metal ions.

    Gravimetric Analysis

    • A weighed sample is dissolved
    • A precipitating agent is added to the solution to produce an insoluble precipitate
    • The precipitate is filtered, dried, or ignited, and then weighed
    • The analyte weight % is calculated from the precipitate weight and relevant gravimetric factors.

    Gravimetric Factor (GF)

    • The weight of the analyte per unit weight of precipitate

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