Self-Ionisation of Water and pH Concepts
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Questions and Answers

Match the following definitions with the correct terms:

Strong Acid = Good proton donor Weak Acid = Poor proton donor Strong Base = Good proton acceptor Weak Base = Poor proton acceptor

Match the following acids with their strength classification:

HCl = Strong Acid H2SO4 = Strong Acid Ethanoic Acid = Weak Acid NH3 = Weak Base

Match the following chemical symbols with their meanings:

K_a = Acid dissociation constant K_b = Base dissociation constant [H^+] = Hydrogen ion concentration [OH^-] = Hydroxide ion concentration

Match the following pH measurement tools with their descriptions:

<p>pH data loggers = Most accurate method of measuring pH Universal indicator paper = Color comparison to a chart pH meters = Electronic devices measuring pH Test strips = Convenient and portable pH measurement</p> Signup and view all the answers

Match the following acid-base reactions with their classifications:

<p>HCl + H2O = Strong acid + weak base CH3COOH + H2O = Weak acid + strong base NaOH + HCl = Strong base + strong acid NH3 + H2O = Weak base + weak acid</p> Signup and view all the answers

Match the following indicators with their respective pH range:

<p>Methyl Orange = 3 -- 5 Litmus = 5 -- 8 Phenolphthalein = 8 - 10 Universal Indicator = 0 -- 14</p> Signup and view all the answers

Match the following indicators with their acid and base colors:

<p>Methyl Orange = Red / Yellow Litmus = Red / Blue Phenolphthalein = Colourless / Pink Bromothymol Blue = Yellow / Blue</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Self-Ionisation of Water = The process where water produces H^+^ and OH^-^ ions pH Scale = A measure of hydrogen ion concentration Kw = Ionic product of water Acidic Solution = A solution with pH less than 7</p> Signup and view all the answers

Match the following values with their meanings:

<p>1 × 10^-14 = Kw at 25°C 7.1 × 10^-7 mol/L = Hydrogen ion concentration for a specific pH 7 = pH of a neutral solution &lt; 7 = pH range of acidic solutions</p> Signup and view all the answers

Match the following components involved in a pH titration:

<p>Burette = Contains the base Beaker = Contains the acid Magnetic stir bar = Keeps the acid stirred pH sensor = Measures the pH</p> Signup and view all the answers

Match the following pH values with their corresponding solution types:

<p>pH &lt; 7 = Acidic solution pH = 7 = Neutral solution pH &gt; 7 = Basic solution pH = 3 = Strong acidic solution</p> Signup and view all the answers

Match the following actions in a titration with their outcomes:

<p>Adding OH^-^ (base) = Favors the reverse reaction Adding H^+^ (acid) = Favors the forward reaction Stirring the acid = Ensures uniform pH Recording pH data = Tracks changes over time</p> Signup and view all the answers

Match the following terms with their definitions or actions:

<p>Le Chatelier's Principle = Predicts the shift in equilibrium pH range of an indicator = Interval of pH with color change Titration = Process of adding acid to base Indicator = Substance that changes color with pH</p> Signup and view all the answers

Match the following formulas with their descriptions:

<p>Kw = [H^+^][OH^-^] = Relationship of hydrogen and hydroxide ions in water pH = -log10[H^+^] = Calculation of acidity based on hydrogen ion concentration Kc = [H^+^][OH^-^]/[H2O] = Equilibrium constant for self-ionisation of water [H^+] = 1 × 10^-7 = Hydrogen ion concentration at neutral pH</p> Signup and view all the answers

Match the following statements with their truths:

<p>Water conducts electricity only when ions are present = True Acidic solutions have a pH of 8 = False OH^-^ ions are produced from water self-ionisation = True pH can be greater than 14 = False</p> Signup and view all the answers

Match the following titration types with their characteristics:

<p>Titrating a Strong Acid against a Strong Base = Large jump of pH at the end point Titrating a Strong Acid against a Weak Base = Methyl orange as a suitable indicator Titrating a Weak Acid against a Strong Base = Phenolphthalein is a suitable indicator Titrating a Weak Acid against a Weak Base = No sudden jump in pH value</p> Signup and view all the answers

Match the acid-base theories with their definitions:

<p>Brønsted-Lowry Theory = Defines an acid as a proton donor Arrhenius Theory = Strong acids nearly completely dissociate in water Conjugate Pair = Acid and base that differ by one proton Indicator Reaction = Changes color due to shifts in hydronium ion concentration</p> Signup and view all the answers

Match the indicators with their suitable titration:

<p>Litmus = Titrating a Strong Acid against a Strong Base Methyl Orange = Titrating a Strong Acid against a Weak Base Phenolphthalein = Titrating a Weak Acid against a Strong Base Not suitable = Titrating a Weak Acid against a Weak Base</p> Signup and view all the answers

Match the pH calculations with their corresponding solutions:

<p>pOH of 0.5 M NaOH = 13.7 pH of 0.5 M NaOH = 14 - 0.3 = 13.7 Calculation of [H^+^] for 0.1 M indicator = 0.00141 pH of 0.1 M indicator solution = 2.85</p> Signup and view all the answers

Match the concepts of strong and weak acids:

<p>Strong Acid = Almost completely dissociates in solution Weak Acid = Partially dissociates in solution Dibasic Acid = Can donate two protons Monobasic Acid = Can donate one proton</p> Signup and view all the answers

Match the experimental setup to the acid-base reaction:

<p>0.1 M NaOH with 0.1 M HCl = Strong Acid against Strong Base 0.1 M NH3 with 0.01 M HCl = Strong Acid against Weak Base 0.1 M NaOH with 0.1 M CH3COOH = Weak Acid against Strong Base 0.01 M NH3 with 0.1 M CH3COOH = Weak Acid against Weak Base</p> Signup and view all the answers

Match the function of hydroxyl ions with its effect in reactions:

<p>Hydroxyl ions = Remove hydrogen ions Reaction shift forward = Caused by addition of hydroxyl ions Color change in indicators = Result of proton concentration shift No endpoint detection = Occurs in Weak Acid against Weak Base titration</p> Signup and view all the answers

Match the chemical formulas with their corresponding substances:

<p>NaOH = Strong base HCl = Strong acid NH3 = Weak base CH3COOH = Weak acid</p> Signup and view all the answers

Match the following pH calculations with their solutions:

<p>0.04 M H2SO4 = pH = 0.097 0.15 M NaOH = pH = 13.18 0.1 M ethanoic acid = pH = 2.9 0.1 M methanoic acid = pH = 2.34</p> Signup and view all the answers

Match the following indicators with their behavior in acid or base:

<p>HIn in acid = Colour 1 is seen HIn in base = Colour 2 is seen Adding H+ = Reverse reaction favored Adding OH- = Forward reaction favored</p> Signup and view all the answers

Match the following acids/bases with their dissociation constants:

<p>Ethanoic acid = Ka = 1.8 x 10^-5 Methanoic acid = Ka = 2.1 x 10^-4 H2SO4 = Strong acid (dissociates completely) NaOH = Strong base (dissociates completely)</p> Signup and view all the answers

Match the following pH scale limitations:

<p>Limited range = 0.1 - 14 Temperature limitation = 25°C Concentration limitation = Does not work at extremely low concentrations Theoretical range = Possible values outside 0 - 14</p> Signup and view all the answers

Match the following formulas for calculating pH:

<p>pH = -log10[H^+] = Calculating pH of acids pOH = -log10[OH^-] = Calculating pH of bases [H^+] = sqrt(Ka x Macid) = Calculating [H^+] for weak acids [OH^-] = sqrt(Kb x Mbase) = Calculating [OH^-] for weak bases</p> Signup and view all the answers

Match the following reactions with their respective components:

<p>H2SO4 dissociation = 2H+ + SO4^2- Weak acid equilibrium = HA ⇌ H+ + A^- NaOH dissociation = Na+ + OH^- Acid-base indicator reaction = HIn ⇌ H+ + In^-</p> Signup and view all the answers

Match the following pH outcomes with their respective substances:

<p>Strong acid = Low pH Strong base = High pH Weak acid = Moderate pH Neutral solution = pH = 7</p> Signup and view all the answers

Match the following acids and their characteristics:

<p>H2SO4 = Strong acid, complete dissociation Ethanoic acid = Weak acid, Ka = 1.8 x 10^-5 Methanoic acid = Weak acid, Ka = 2.1 x 10^-4 NaOH = Strong base, complete dissociation</p> Signup and view all the answers

Study Notes

Self-Ionisation of Water

  • Water conducts electricity when ions are present
  • Pure water conducts a small current due to self-ionisation
  • H₂O ⇌ H⁺ + OH⁻
  • Equilibrium favors the left side, concentrations of H⁺ and OH⁻ are very small
  • The concentration of H₂O is considered constant
  • Equilibrium constant (K) = [H⁺][OH⁻]/[H₂O]
  • Kw = lonic product of water, Kw = 1 x 10⁻¹⁴ at 25°C
  • [H⁺] = 1 x 10⁻⁷ mol/L, [OH⁻] = 1 x 10⁻⁷ mol/L for pure water

pH Scale

  • pH = -log₁₀[H⁺]
  • Concentration is in moles per litre
  • pH of a solution measures the concentration of hydrogen ions
  • Value ranges from 0-14
  • pH less than 7 = acidic
  • pH greater than 7 = alkaline
  • pH 7 = neutral

Strengths of Acids and Bases

  • Strong acid: Good proton donor. Example: HCl, H₂SO₄. Completely dissociates in water.

  • Weak acid: Poor proton donor. Example: Ethanoic acid. Slightly dissociates in water.

  • Strong base: Good proton acceptor. Example: NaOH, KOH. Completely dissociates in water.

  • Weak base: Poor proton acceptor, Example: NH₃. Slightly dissociates in water.

  • Ka: Acid dissociation constant

  • Kb: Base dissociation constant

Calculating pH of Strong Acids and Bases

  • Strong acids and bases fully dissociate in water, so assume complete dissociation when calculating pH
  • Example: 0.4 M H₂SO₄ solution produces 0.8 moles of H⁺ ions, pH of ~0.1
  • pH of a strong base: pOH = -log₁₀[OH⁻] then pH=14-pOH

Limitations of the pH Scale

  • The pH scale is limited to the range 0.1 - 14, theoretically possible outside
  • Applicable to dilute aqueous solutions at 25°C
  • Does not work at extremely low concentrations

Calculating pH of Weak Acids and Bases

  • To find pH of a weak acid or base, need the dissociation constant
  • Example: Calculating pH of 0.1 M ethanoic acid using Ka = 1.8 x 10⁻⁵, results in a pH of ~2.9

Acid-Base Indicators

  • A substance that changes color based on the solution's pH
  • Indicators are weak acids or bases; color change occurs with pH changes
  • The indicator shows a clear range of color change, useful for titration
  • Examples include: Methyl Orange and Phenolphthalein

pH Titration

  • Experiment measuring pH change during acid-base reaction
  • Acid in beaker, base in burette, pH measured as base added
  • Curve of pH versus volume plotted; The equivalence point on the curve helps determine the endpoint
  • Titrating strong acid vs strong base - large change in pH near endpoint
  • Titrating weak acid vs strong base - large change in pH near endpoint
  • Titrating weak acid vs weak base - small change in pH near endpoint. No clear endpoint

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pH and Indicators PDF

Description

Explore the fundamental concepts of self-ionisation of water, the pH scale, and the strengths of acids and bases. This quiz covers essential definitions, equilibrium expressions, and the behavior of various acids and bases in solution. Test your understanding of how these concepts interact in the realm of chemistry.

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