Proton Transfer Reactions (DP IB Chemistry)

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  • Define Brønsted-Lowry acid?

    A Brønsted-Lowry acid is a species that gives away a proton (H+).

  • Define Brønsted-Lowry base?

    A Brønsted-Lowry base is a species that accepts a proton (H+).

  • In the following reaction, which species is acting as a Brønsted-Lowry acid?

    HCl (aq) + H2O (l) → Cl- (aq) + H3O+ (aq)

    In the following reaction, HCl (aq) is acting as a Brønsted-Lowry acid.

    HCl (aq) + H2O (l) → Cl- (aq) + H3O+ (aq)

  • In the following reaction, which species is acting as a Brønsted-Lowry base?

    HCl (aq) + H2O (l) → Cl- (aq) + H3O+ (aq)

    In the following reaction, H2O (l) is acting as a Brønsted-Lowry base.

    HCl (aq) + H2O (l) → Cl- (aq) + H3O+ (aq)

  • True or False?

    All bases are alkalis.

    False.

    Not all bases are alkalis.

  • True or False?

    An alkali is a soluble base.

    True.

    An alkali is a soluble base.

  • In the following reaction, which species is acting as a Brønsted-Lowry acid?

    HCl (g) + NH3 (g) → NH4Cl (s)

    In the following reaction, HCl (l) is acting as a Brønsted-Lowry acid.

    HCl (g) + NH3 (g) → NH4Cl (s)

  • In the following reaction, which species is acting as a Brønsted-Lowry base?

    HCl (g) + NH3 (g)  ⇌ NH4Cl (s)

    In the following reaction, NH3 (g) is acting as a Brønsted-Lowry base.

    HCl (g) + NH3 (g) ⇌ NH4Cl (s)

  • In the following reaction, what species is acting as a Brønsted-Lowry base?

    H2PO4(aq) + H2O (l) → HPO42− (aq) + H3O+ (aq)

    In the following reaction, H2O (l) is acting as a Brønsted-Lowry base.

    H2PO4(aq) + H2O (l) → HPO42− (aq) + H3O+ (aq)

  • In the following reaction, what species is acting as a Brønsted-Lowry acid?

    H2PO4(aq) + H2O (l) → HPO42− (aq) + H3O+ (aq)

    In the following reaction, H2PO4(aq) is acting as a Brønsted-Lowry acid.

    H2PO4(aq) + H2O (l) → HPO42− (aq) + H3O+ (aq)

  • True or False?

    A proton in aqueous solution can be represented as H+ (aq) only.

    False.

    A proton in aqueous solution can be represented as both H+ (aq) and H3O+ (aq).

  • What is meant by conjugate acid-base pair?

    A conjugate acid-base pair is two species that are different from each other by a H+ ion.

  • In the following reaction, what is the acid and conjugate base pair?

    H2CO3 (aq) + OH- (aq) ⇌ HCO3- (aq) + H2O (l)

    In the following reaction, the acid and conjugate base pair is H2CO3 (aq) and HCO3- .

    H2CO3 (aq) + OH- (aq) ⇌ HCO3- (aq) + H2O (l)

  • In the following reaction, what is the base and conjugate acid pair?

    H2PO4(aq) + CN- (aq) ⇌  HCN (aq)  + HPO42− (aq)

    In the following reaction, the base and conjugate acid pair is CN- (aq) and HCN (aq) .

    H2PO4(aq) + CN- (aq) ⇌  HCN (aq)  + HPO42− (aq)

  • In the following reaction, what is the acid and conjugate base pair?

    HSO4- (aq) + OH- (aq) ⇌ SO4- (aq) + H2O (l)

    In the following reaction, the acid and conjugate base pair is HSO4- (aq) and SO4- (aq).

    HSO4- (aq) + OH- (aq) ⇌ SO4- (aq) + H2O (l)

  • In the following reaction, what is the acid and conjugate base pair?

    HCO3- (aq) + H2O (l)  ⇌ CO32- (aq) + H3O+ (aq)

    In the following reaction, the acid and conjugate base pair is HCO3- (aq) and CO32- (aq).

    HCO3- (aq) + H2O (l)  ⇌ CO32- (aq) + H3O+ (aq)

  • True or False?

    In the following reaction the acid on the left hand side has a conjugate acid on the right hand side.

    H2SO4 + HNO3 ⇋  H2NO3+ + HSO4-

    False.

    In the following reaction the acid on the left hand side has a conjugate base on the right hand side.

    H2SO4 + HNO3 ⇋  H2NO3+ + HSO4-

  • What is the conjugate acid in the following reaction?

    CH3COOH + HCl  ⇌ CH3COOH2+ + Cl-

    The conjugate acid in the reaction is CH3COOH2+.

    CH3COOH + HCl  ⇌ CH3COOH2+ + Cl-

  • What is the conjugate base of NH4+?

    The conjugate base of NH4+ is NH3.

  • True or False?

    The conjugate base of a strong acid is a weak base.

    True.

    The conjugate base of a strong acid is a weak base.

  • What is the relationship between the strength of an acid and its conjugate base?

    The relationship between the strength of an acid and its conjugate base is:

    The stronger the acid, the weaker its conjugate base.

  • Define amphiprotic.

    Amphiprotic is a term describing species that can act both as proton donors and acceptors.

  • True or False?

    Water is an example of an amphiprotic species.

    True.

    Water is an example of an amphiprotic species.

  • What is an amphoteric compound?

    An amphoteric compound has both basic and acidic character.

  • True or False?

    All amphiprotic substances are amphoteric.

    True.

    All amphiprotic substances are amphoteric.

  • True or False?

    All amphoteric substances are amphiprotic.

    False.

    Not all amphoteric substances are amphiprotic.

    For example, aluminium oxide is amphoteric but not amphiprotic.

  • True or False.

    Amphiprotic substances can only accept protons.

    False.

    Amphiprotic substances can both accept or donate protons.

  • In the following equation, is Al2O3 acting as an acid or base?

    Al2O3 (s) + 2NaOH (aq) + 3H2O (l) → 2NaAl(OH)4 (aq)     

    In the following equation is Al2O3 is acting as an acid.

    Al2O3 (s) + 2NaOH (aq) + 3H2O (l) → 2NaAl(OH)4 (aq)     

  • True or False.

    HCO3 is amphiprotic.

    True.

    HCO3 is amphiprotic.

  • Define pH.

    pH is the negative logarithm of the hydrogen ion concentration in mol dm-3

    pH = -log[H+]

  • What does the pH scale measure?

    The pH scale measures how acidic or basic a substance is.

  • True or False?

    The pH scale is linear.

    False.

    The pH scale is logarithmic.

  • What is the pH range for acidic solutions?

    The pH range for acidic solutions is 0-6 .

  • What is the pH range for alkaline solutions?

    The pH range for alkaline solutions is 8-14.

  • What is the most accurate way of measuring pH?

    The most accurate way of measuring pH is using a pH meter.

  • What is the pH of a neutral solution at 298K?

    The pH of a neutral solution at 298K is 7.

  • How does pH change as [H+] increases?

    As [H+] increases, pH decreases.

  • True or False?

    A solution with pH 4 is 10 times more acidic than a solution with pH 5.

    True.

    A solution with pH 4 is 10 times more acidic than a solution with pH 5.

  • What is the pH of a solution that has an H+ concentration of 0.001 mol dm-3 at 298 K?

    The pH of a solution that has an H+ concentration of 0.001 mol dm-3 at 298 Kis pH 3.

  • In alkaline solutions which ions are in a greater concentration than H+ ions?

    In alkaline solutions OH- ions are in a greater concentration than H+ ions.

  • True or False?

    Using universal indicator is a more accurate method is to measure the pH of a substance than a using a pH meter.

    False.

    Using universal indicator is a less accurate method is to measure the pH of a substance than a using a pH meter.

  • Calculate the pH of HCl with a concentration of 0.43 mol dm-3.

    pH = -log[H+]

    The pH of HCl with a concentration of 0.43 mol dm-3 is 0.37.

    pH = -log[0.43]

    pH = 0.37

  • Write the equation for the equilibrium established in water.

    An equation for the equilibrium established in water is:

    H2O (l) ⇌ H+ (aq) + OH- (aq).

  • State the equation for the ion product of water.

    The equation for the ion product of water is:

    Kw = [H+][OH-]

  • True or False?

    The value of Kw remains constant at all temperatures.

    False.

    The value of Kw changes with temperature.

  • How does increasing temperature affect Kw?

    As temperature increases, Kw increases.

  • What is the relationship between [H+] and [OH-] in pure water at 298 K?

    In pure water at 298K, [H+] = [OH-].

  • True or False?

    In acidic solutions, [H+] > [OH-].

    True.

    In acidic solutions, [H+] > [OH-].

  • True or False?

    In alkaline solutions, [H+] < [OH-].

    True.

    In alkaline solutions, [H+] < [OH-].

  • How does the pH of water change with increasing temperature?

    As temperature increases, the pH of water decreases.

  • Is the ionisation of water exothermic or endothermic?

    The ionisation of water is endothermic.

  • A solution of sodium hydroxide, NaOH (aq) has a concentration of 1.0 × 10−4 mol dm−3 ?

    (Kw = 1.0 × 10−14 at 298 K)

    What is the pH of the solution?

    The pH of a solution of sodium hydroxide, NaOH (aq) of concentration 1.0 × 10−4 mol dm−3 is 10.

    • Kw = [H+] [OH-]

    • Rearranging gives [H+]  = Kw ÷ [OH-]

    • [H+] = (1.0 × 10−14) ÷ (1.0 × 10−4) = 1.0 × 10−10 mol dm−3

    • pH = – log10[1.0 × 10−10 (aq)]

    • So the pH = 10

  • Why is [H2O (l)] not included in the expression for Kw?

    [H2O (l)] not included in the expression for Kw a s the concentration of water molecules remains constant.

  • Define strong acid.

    A strong acid is an acid that dissociates almost completely in aqueous solutions.

  • Define weak acid.

    A weak acid is an acid that partially (or incompletely) dissociates in aqueous solutions.

  • True or False?

    Weak acids are proton donors and their solutions are poor conductors.

    True.

    Weak acids are proton donors and their solutions are poor conductors.

  • Define strong base.

    A strong base is a base that dissociates almost completely in aqueous solutions.

  • True or False?

    HCl, HBr, HI, HNO3 and H2SO4 are all strong acids.

    True.

    HCl, HBr, HI, HNO3 and H2SO4 are all strong acids.

  • Give an example of a strong base.

    Examples of strong bases include Group 1 hydroxides (e.g. NaOH, KOH)

  • Which is a stronger acid, HBr or HI?

    HI is a stronger acid than HBr.

    This is because the HI bond is a longer bond than HBr and is weaker. Therefore H+ ions are more easily released.

  • Do strong or weak acids conduct electricity better?

    Strong acids conduct electricity better than weak acids.

    A stronger acid has a higher concentration of H+ so it conducts electricity better.

  • Which acid has a higher pH?

    CH3CH2COOH or HNO3

    CH3CH2COOH has a higher pH than HNO3.

  • Why do strong acids react more vigorously than weak acids?

    Strong acids react more vigorously because the concentration of H+ is greater in strong acids compared to weak acids.

  • Write an equation for the ionisation of ethanoic acid.

    The equation for the ionisation of ethanoic acid is:

    CH3COOH (aq)rightwards harpoon over leftwards harpoonCH3COO- (aq) + H+ (aq)

  • Why are stronger acids better at conducting electricity than weak acids?

    A strong acid has a higher concentration of H+ ions so it conducts electricity better than a weak acid.

  • Why are weak acids less acidic than strong acids?

    Weak acids are less acidic than strong acids as they contain fewer H+ in solution. This is because they only partially ionise.

  • Give an example of a weak base.

    Weak bases include:

    • NH3

    • Amines

    • Some transition metal hydroxides

  • True or False?

    In general, strong acids produce strong conjugate bases and weak acids produce weak conjugate bases.

    False.

    In general, strong acids produce weak conjugate bases and weak acids produce strong conjugate bases.

  • Write the ionic equation to show how a base accepts hydrogen ions.

    The ionic equation to show how a base accepts hydrogen ions is:

    OH– (aq) +  H+ (aq)  ⇌  H2O (l)

  • HNO3 dissociates to form H+ and NO3- ions.

    Is the NO3- ion a strong or weak conjugate base?

    HNO3 dissociates to form H+ and NO3- ions.

    The NO3- ion is a weak conjugate base.

  • True or False?

    A solution of 10 mol dm-3 HCN is a concentrated weak acid.

    True.

    A solution of 10 mol dm-3 HCN is a concentrated weak acid.

  • Define neutralisation reaction.

    A neutralisation reaction is one in which an acid and a base/alkali react together to form water and a salt

  • What type of salt is produced if an alkali is added to sulfuric acid?

    A sulfate salt is produced when sulfuric acid is reacted with an alkali.

  • What type of salt is produced if an alkali is added to nitric acid?

    A nitrate salt is produced when nitric acid is reacted with an alkali.

  • What type of salt is produced if an alkali is added to hydrochloric acid?

    A chloride salt is produced when hydrochloric acid is reacted with an alkali.

  • What acid is used to make ethanoate salts?

    Ethanoic acid is used to make ethanoate salts.

  • State the general equation for the reaction between an acid and a metal hydroxide.

    The general equation for the reaction between an acid and a metal hydroxide is:

    acid + metal hydroxide → salt + water

  • Write the symbol equation for the reaction between hydrochloric acid  + potassium hydrogencarbonate.

    The equation for the reaction between hydrochloric acid  + potassium hydrogencarbonate is:

    HCl (aq) + KHCO3 (s) → KCl (aq) + H2O (l) + CO2 (g)

  • Write the equation for the reaction between nitric acid + copper carbonate .

    The equation for the reaction between nitric acid + copper carbonate is:

    2HNO(aq) + CuCO(s) → Cu(NO3)2 (aq) + H2O (l) + CO2 (g)

  • Write the equation for the reaction between sulfuric acid + barium hydroxide.

    The equation for the reaction between sulfuric acid + barium hydroxide is:

    H2SO(aq) + Ba(OH)2 (aq) → BaSO(s) + 2H2O (l)

  • What salt is formed when sulfuric acid reacts with ammonia?

    Ammonium sulfate is formed when sulfuric acid reacts with ammonia.

  • What base could be used to form copper(II) chloride?

    Bases that could be used to form copper(II) chloride are copper(II) oxide, copper(II) hydroxide, copper(II) carbonate.

  • Name the piece of equipment that can be used to measure the pH during a titration to plot a curve.

    During a titration, a pH meter can be used and a pH curve plotted.

  • What is point X called?

    A pH curve showing the midpoint of the inflection which is the equivalence point.

    X is the equivalence or stoichiometric point.

    A pH curve showing the midpoint of the inflection which is the equivalence point.
  • What is the pH at the equivalence point of a titration between HCl and NaOH?

    The pH at the equivalence point of a titration between HCl and NaOH is 7.

  • What four pieces of information can be obtained from a pH curve?

    From a pH curve, you can determine:

    • The initial pH of the acid

    • The pH at the equivalence point

    • The volume of base at the equivalence point

    • The range of pH at the vertical section of the curve

  • What is the pH at the start of the titration?

    A graph to show the pH curve of a strong base and weak acid

    The pH at the start of the titration is pH 3.

    A graph to show the pH curve of a strong base and weak acid
  • What is the pH at equivalence point?

    A graph to show the pH curve of a strong base and weak acid

    The pH at equivalence point is pH 8.

    A graph to show the pH curve of a strong base and weak acid
  • What volume of NaOH (aq), in cm3, was added to reach equivalence point?

    A graph to show the pH curve of a strong base and weak acid

    The volume of NaOH (aq) that was added to reach the equivalence point is 30 cm3.

    A graph to show the pH curve of a strong base and weak acid
  • What is the equivalence point strong acid and strong base titration?

    The equivalence point strong acid and strong base titration is pH 7.

  • True or False?

    The equivalence point for a weak acid and strong base titration is below 7.

    False.

    The equivalence point for a weak acid and strong base titration is above 7.

  • True or False?

    The equivalence point for a strong acid and weak base titration is below 7.

    True.

    The equivalence point for a strong acid and weak base titration is below 7.

  • What is the half equivalence point?

    The half equivalence point is the stage of the titration at which exactly half the amount of weak acid has been neutralised.

  • What is labelled X?

    pH curve to show the half equivalence point

    X is the half equivalence point.

    pH curve to show the half equivalence point
  • What region is labelled X?

    pH curve to show the buffer region labelled

    The region that is labelled X is the buffer region.

    pH curve to show the buffer region labelled
  • What is the relationship between half equivalence point and pH and pOH?

    pKa = pH at half equivalence 

    AND

    pKb = pOH at half equivalence 

  • True or False?

    [NH3 (aq)] = [NH4+ (aq)] at the half equivalence point during a titration involving NH3 (aq) and HCl (aq).

    True.

    [NH3 (aq)] = [NH4+ (aq)] at the half equivalence point during a titration involving NH3 (aq) and HCl (aq)

  • What type of pH curve is shown below?

    pH curve showing a weak acid and a weak base

    A weak acid and weak base pH curve is shown.

    pH curve showing a weak acid and a weak base
  • What type of pH curve is shown below?

    pH curve to show a strong acid and weak base.

    A weak base and strong acid pH curve is shown below.

    pH curve to show a strong acid and weak base.
  • What is the pH at the y-intercept in the pH curve below?

    pH curve to show a strong acid and weak base.

    The pH at the y-intercept is pH 11.

    pH curve to show a strong acid and weak base.
  • What is the pH when [H+] is 2.80 x 10-3 mol dm-3 at 298 K?

    pH = -log[H+]

    The pH when [H+] is 2.80 x 10-3 mol dm-3 is:

    pH = -log[H+]

    pH = -log [2.80 x 10-3 ]

    pH = 2.55

  • What is the conversion for pH to [H+]?

    pH = -log[H+]

    The conversion for pH to H+ concentration is:

    [H+]= 10-pH .

  • What is [H+] when the pH is 1.89 at 298 K?

    pH = -log[H+]

    [H+] when the pH is 1.89 is 0.013 mol dm-3 at 298 K.

    [H+]= 10-pH

  • What is the pH of 0.75 mol dm-3 sodium hydroxide, NaOH.

     Kw = 1 x 10-14 at 298 K

    The pH of 0.75 mol dm-3 sodium hydroxide, NaOH is:

    • [H+] = Kw  ÷ [OH]

    • [H+] = (1 x 10-14) ÷ 0.75 = 1.33 x 10-14

    • pH = -log 1.33 x 10-14  = 13.88

  • How can [OH-] be calculated from pOH?

    pOH = -log[OH-]

    [OH-] can be calculated from pOH by:

    [OH-] = 10-pOH

  • State the equation to calculate [H+] from Kw and [OH-].

    Kw = [OH-] [H+]

    The equation to calculate [H+] from Kw and [OH-] is:

    [H+] = fraction numerator K subscript w over denominator open square brackets O H to the power of minus close square brackets end fraction

  • True or False?

    pH can be calculated by pH = 14 - pOH.

    True.

    pH can be calculated by pH = 14 - pOH.

  • Calculate the pH of NaOH with a concentration of 0.49 mol dm3 using the equation pH = 14 - pOH.

    pOH = -log[OH-]

    To calculate the pH of NaOH with a concentration of 0.49 mol dm3 using the equation pH = 14 - pOH:

    • pOH = -log [0.49] = 0.31

    • pH = 14 - 0.31 = 13.69

  • True or False?

    pH x pOH = pKw

    False.

    pH + pOH = pKw

  • What is the acid dissociation constant, Ka for the acid HA?

    The acid dissociation constant, Ka, for the acid HA is:

    Ka = fraction numerator open square brackets H to the power of plus close square brackets open square brackets A to the power of minus close square brackets over denominator open square brackets H A close square brackets end fraction

  • What is the base dissociation constant, Kb, for C6H5CH2NH2?

    The base dissociation constant, Kb, for C6H5CH2NH2 is:

    Kb = fraction numerator open square brackets C subscript 6 H subscript 5 C H subscript 2 N H subscript 3 to the power of plus close square brackets open square brackets O H to the power of minus close square brackets over denominator open square brackets C subscript 6 H subscript 5 C H subscript 2 N H subscript 2 close square brackets end fraction

  • The pKa of benzoic acid is 4.18.

    What is its Ka?

    The Ka of benzoic acid is 6.61 x 10–5.

    • Ka= 10-pKa

    • Ka= 10-4.18

    • Ka = 6.61 x 10–5

  • What is the relationship between Ka, Kb and Kw?

    The relationship between Ka, Kb and Kw is:

    Ka x Kb = Kw

  • What is the relationship between pKa, pKb and pKw?

    The relationship between pKa, pKb and pKw is:

    pKa + pKb = pKw

  • True or False?

    The larger the pKa value, the weaker the acid.

    True .

    The larger the pKa value, the weaker the acid.

  • True or False?

    The smaller the Kb value, the stronger the base.

    False.

    The larger the Kb value, the stronger the base.

  • What is the acid dissociation constant, Ka, for propanoic acid?

    The acid dissociation constant, Ka, for propanoic acid is:

    K subscript straight a space equals space fraction numerator stretchy left square bracket CH subscript 3 CH subscript 2 COO to the power of minus stretchy right square bracket stretchy left square bracket straight H to the power of plus stretchy right square bracket over denominator stretchy left square bracket CH subscript 3 CH subscript 2 COOH stretchy right square bracket end fraction

  • Hydrocyanic acid has a Ka of 6.17 x 10-10.

    What is its pKa?

    The pKa of hydrocyanic acid is 9.21.

    • pKa = -logpKa

    • pKa = -log 6.17 x 10-10 = 9.21

  • The pKb of CH(Cl2)COO- is 12.65.

    What is the pKa value of CH(Cl2)COOH?

    The pKa value of CH(Cl2)COOH is 1.35.

    • pKa + pKb = 14

    • 14 - pKb

    • 14 - 12.65 = 1.35

  • What is the [H+] in a 0.15 mol dm-3 solution which has a Ka of 1.00 x 10-8 at 298 K?

    The [H+] in a 0.15 mol dm-3 solution whose Ka = 1.00 x 10-8 at 298 K is 3.87 x 10-5.

    • Kafraction numerator left square bracket straight H to the power of plus right square bracket squared over denominator 0.15 end fraction = 1.00 x 10-8

    • [H+]2 = 1.5 x 10-9

    • [H+] = 3.87 x 10-5 (mol dm-3)

  • What is the [OH-] of a solution with a [H+] of 4.50 x 10-6 mol dm3 at 298 K?

    Kw = [H+][OH-]

    At 298K, Kw is 1 x 10-14 mol2 dm-6

    The [OH-] of a solution with a [H+] of 4.50 x 10-6 mol dm3 at 298 K is:

    • [OH-] = fraction numerator K subscript w over denominator left square bracket straight H to the power of plus right square bracket end fraction equals space fraction numerator 1.00 space cross times 10 to the power of minus to the power of 14 over denominator 4.50 space cross times space 10 to the power of negative 6 end exponent end fraction space= 2.22 x 10-9 mol dm-3

  • What is the acid dissociation constant, Ka, at 298 K for a 0.50 mol dm-3 solution of propanoic acid with a [H+] of 1.75 x 10-5?

    The acid dissociation constant, Ka, at 298 K for a 0.50 mol dm-3 solution of propanoic acid with a [H+] of 1.75 x 10-5 is:

    • Kafraction numerator open square brackets straight H to the power of plus close square brackets squared over denominator open square brackets CH subscript 3 CH subscript 2 COOH close square brackets end fraction

    • Ka = fraction numerator open parentheses 1.75 space cross times 10 to the power of negative 5 end exponent close parentheses squared over denominator 0.50 end fraction

    • Ka = 6.13 × 10-10

  • What is the relationship of Ka and Kb for a conjugate acid-base pair?

    The relationship of Ka and Kb for a conjugate acid-base pair is Ka x Kb = Kw.

  • What is the pH of a 0.04 mol dm-3  solution of NaOH at 298 K?      

    Kw = [H+][OH-]

    At 298K, Kw is 1 x 10-14 mol2 dm-6.

    The pH of a 0.04 mol dm-3  solution of NaOH at 298 K is:

    • [H+] = begin mathsize 14px style fraction numerator K subscript straight w over denominator left square bracket OH to the power of minus right square bracket end fraction end stylefraction numerator 1 blank cross times blank 10 to the power of negative 14 end exponent over denominator 0.04 end fraction = 2.5 x 10-13

    • pH = -log(2.5 x 10-13)

    • pH = 12.60

  • What is the [OH-] of 0.05 mol dm-3 ammonia solution, NH3 (aq)?

    Kb NH3 = 1.78 x 10-5 at 298K.

    The [OH-] of 0.05 mol dm-3 ammonia solution, NH3 (aq) is:

    • Kb = fraction numerator open square brackets N H subscript 4 to the power of plus close square brackets open square brackets O H to the power of minus close square brackets over denominator open square brackets N H subscript 3 close square brackets end fraction

    • [OH-]2 = 1.78 x 10-5 x 0.05

    • [OH-] = 9.43 x 10-4 mol dm-3

  • Why does the salt NaCl not change the pH of a solution?

    The Na+ and Cl- ions do not act as Brønsted-Lowry acids or bases as they can not release or accept H+ ions.

  • Is NH4Cl (aq) an acidic, neutral or alkaline salt?

    NH4Cl is an acidic salt as it is formed from NH3 (aq) (weak base) and HCl (aq) (strong acid)

  • Write an equation to show how NH4+ reacts with water.

    An equation to show how NH4+ reacts with water.

    NH4+ (aq) + H2O (l) → H3O+ (aq) + NH3 (aq) 

  • Is CH3COONa (aq) an acidic, neutral or alkaline salt?

    CH3COONa (aq) is an alkaline salt as it is formed from NaOH (aq) (strong base) and CH3COOH (aq) (weak acid).

  • Write an equation to show how CH3COO (aq) reacts with water.

    An equation to show how CH3COO (aq)+ reacts with water is:

    CH3COO (aq) + H2O (l) → CH3COOH (aq) + OH- (aq)

  • True or False?

    If the salt is formed from a weak acid and weak base then its hydrolysis is determined by the relative Ka and Kb values.

    True.

    If the salt is formed from a weak acid and weak base then its hydrolysis is determined by the relative Ka and Kb values.

  • True or False?

    If a salt is formed from a strong acid and strong base titration then it is alkaline.

    False.

    If a salt is formed from a strong acid and strong base titration then it is neutral.

  • Is the K2CO3 salt acidic, basic or neutral?

    The K2CO3 salt is alkaline as it is formed from KOH (aq) (strong bae) and H2CO3 (aq) (weak acid).

  • Is the KNO3 salt acidic, basic or neutral?

    The KNO3 salt is neutral as it is formed from KOH (aq) (strong base) and HNO3 (aq) (strong acid).

  • True or False?

    The NaHCO3 salt is alkaline by hydrolysis.

    True.

    The NaHCO3 salt is alkaline by hydrolysis as it is formed from NaOH (aq) (strong base) and H2CO3 (aq) (weak acid).

  • Define acid-base indicator.

    Acid-base indicators are weak acids, where the components of the conjugate acid–base pair have different colours.

  • Write an equation for the dissociation of the weak acid HIn.

    An equation for the dissociation of the weak acid HIn.

    HIn (aq)   ⇌ H+ (aq) + In– (aq)

  • Write the acid dissociation constant, Ka, for the weak acid HIn.

    The acid dissociation constant, Ka, for the weak acid HIn is:

    Ka = fraction numerator open square brackets H to the power of plus close square brackets open square brackets I n to the power of minus close square brackets over denominator open square brackets H I n close square brackets end fraction

  • The dissociation of the indicator phenolphthalein can be represented as:

    H-Phen   ⇌ H+ + Phen-

    Which direction will the equilibrium shift in acidic conditions?

    The equilibrium will shift to the left in acidic conditions.

    H-Phen   ⇌ H+ + Phen-

  • True or False?

    The pKof an indicator is the same as the pH of its endpoint.

    True.

    The pKof an indicator is the same as the pH of its endpoint.

  • Which indicator is a mixture of many indicators with a wide range of colour change?

    The indicator is a mixture of many indicators with a wide range of colour change is universal indicator.

  • The dissociation of the indicator methyl orange can be represented as:

    H-MO   ⇌ H+ + MO-

    Which direction will the equilibrium shift in at a high pH?

    The equilibrium will shift to the right at a high pH as H+ ions will be mopped up by OH- ions introduced. Therefore the H+ ions need to be replenished by the equilibrium shifting to the right hand side.

  • True or False?

    An appropriate indicator for a titration has an end point range that coincides with the pH at the equivalence point.

    True.

    An appropriate indicator for a titration has an end point range that coincides with the pH at the equivalence point.

  • Define end point.

    The end point is the point where the indicator changes colour during a titration.

  • Define equivalence point.

    The equivalence point in a titration refers to a point at which the added titrant is chemically equivalent to the sample analyte.

    OR

    At the equivalence point in an acid-base titration, moles of base = moles of acid and the solution only contains salt and water.

  • Methyl red has a pKa value of 5.1. What type of titration is methyl red suitable for?

    Methyl red is suitable for a strong acid and weak base titration.

  • True or False?

    Phenolphthalein has a pKa of 9.6 so is suitable for a strong base and weak acid titration.

    True.

    Phenolphthalein has a pKa of 9.6 so is suitable for a strong base and weak acid titration.

  • Why does a weak acid and weak base titration not have a suitable indicator?

    In weak acid and weak base titrations, there is no sudden pH change at the end-point and thus there are no suitable indicators for these titrations.

  • True or False?

    The indicator changes colour when the pH = fraction numerator p K subscript a over denominator p K subscript I n end subscript end fractionof the acid.

    True.

    The indicator changes colour when the pH = pKa of the acid.

  • What is a buffer solution?

    buffer solution is a solution which resists changes in pH when small amounts of acid or base are added.

  • What is a buffer made from?

    A buffer can consist of weak acid – conjugate base or weak base – conjugate acid.

  • Write the equation for the ionisation of sodium ethanoate.

    The equation for the ionisation of sodium ethanoate is:

    CH3COONa + aq → Na+ (aq) + CH3COO- (aq) 

  • Write the equation for the ionisation of ethanoic acid.

    The equation for the ionisation of ethanoic acid is:

    CH3COOH (aq) ⇌ H(aq) + CH3COO- (aq) 

  • What is the composition of a basic buffer?

    The composition of a basic buffer is a weak base and its salt.

  • What is formed when OH- ions are added to an acidic buffer?

    Water is formed when OH- are added to an acidic buffer.

    OH (aq) + H+  (aq) → H2O (l)

  • True or False?

    When OH- ions are added to an acidic buffer, CH3COOH molecules ionise to form more H+ and CH3COO until equilibrium is re-established.

    True.

    When OH- ions are added to an acidic buffer, CH3COOH molecules ionise to form more H+ and CH3COO until equilibrium is re-established.

  • What happens to the equilibrium if acid is added to an acidic buffer containing HA?

    When an acid is added to an acidic buffer Hions react with A ions to form more HA until equilibrium is re-established.

  • Write the equation to show how NH3 (aq) reacts with water.

    The equation to show how NH3 (aq) reacts with water by:

    NH3 (aq) + H2O (l)rightwards harpoon over leftwards harpoon NH4+ (aq) + OH (aq)

  • Write the equation to show what happens when acid is added to a basic buffer which contains ammonia.

    The equation to show what happens when acid is added to a basic buffer which contains ammonia is:

    NH3 (aq) + H+ (aq)rightwards harpoon over leftwards harpoon NH4+ (aq) 

  • What is a basic buffer made from?

    A basic buffer is made by mixing a solution of a weak base with its salt.

  • True or False?

    A basic buffer contains NH3 (aq) and NH4Cl (aq).

    If a base is added, OH ions will combine with the acid NH4+ and form NH3 and H2O.

    True.

    A basic buffer contains NH3 (aq) and NH4Cl (aq). If a base is added OH ions will combine with the acid NH4+ and form NH3 and H2O.

    NH4+ (aq) + OH (aq) rightwards harpoon over leftwards harpoonNH3 (aq) + H2O (l)

  • What two factors does the pH of a buffer depend upon?

    The pH of a buffer solution depends on:

    • The pKa or pKb of its acid or base.

    • The ratio of the concentration of acid or base to the concentration of the conjugate base or acid.

  • State the equation to calculate [H+] of an acidic buffer solution.

    The equation to calculate the [H+] of an acidic buffer solution is:
    open square brackets straight H to the power of plus close square brackets space equals space K subscript straight a space fraction numerator open square brackets acid close square brackets over denominator open square brackets salt close square brackets end fraction

  • State the equation to calculate [OH-] of a basic buffer solution.

    The equation to calculate [OH-] of a basic buffer is:

    [OH] = Kb begin mathsize 14px style fraction numerator open square brackets base close square brackets over denominator open square brackets salt close square brackets end fraction end style

  • True or False?

    Temperature does not change the pH of a buffer solution.

    False.

    A constant temperature must be maintained when using buffers as temperature will influence the pH of the solution

  • True or False?

    Dilution does not change the pH of a buffer solution.

    True.

    Dilution does not change the ratio of acid or base to the salt concentration as both components will be decreased by the same amount

  • Calculate [H+] of a buffer solution containing 0.45 mol dm-3 of ethanoic acid and 0.36 mol dm-3 sodium ethanoate.

    The Ka of ethanoic acid  = 1.74 × 10-5 at 298 K

    To calculate [H+] of a buffer solution containing 0.45 mol dm-3 of ethanoic acid and 0.36 mol dm-3 sodium ethanoate:

    • open square brackets straight H to the power of plus close square brackets space equals space K subscript straight a space fraction numerator open square brackets acid close square brackets over denominator open square brackets salt close square brackets end fraction

    • open square brackets straight H to the power of plus close square brackets space equals space 1.74 space cross times 10 to the power of negative 5 end exponent cross times fraction numerator 0.45 over denominator 0.36 end fraction = 2.18 x 10-5 mol dm-3