IBChemistry: HLDPTopic Questions18. Acids & Bases (HL only)18.2 Calculations Involving Acids & Bases

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First teaching 2014

Last exams 2024

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Calculations Involving Acids & Bases (DP IB Chemistry: HL)

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18.2 Calculations Involving Acids & Bases

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18.2 Calculations Involving Acids & Bases

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1
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Which of the following is the acid dissociation, Ka, constant for ethanoic acid? 

  • CH3COOH 

  • fraction numerator left square bracket CH subscript 3 COO to the power of minus right square bracket left square bracket straight H to the power of plus right square bracket over denominator left square bracket CH subscript 3 COOH right square bracket end fraction

  • fraction numerator left square bracket CH subscript 3 COOH right square bracket over denominator left square bracket CH subscript 3 COO to the power of minus right square bracket left square bracket straight H to the power of plus right square bracket end fraction

  • left square bracket CH subscript 3 COO to the power of minus right square bracket left square bracket straight H to the power of plus right square bracket

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2
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At the same concentration, which acid would have the lowest pH?

  • C6H5COOH Ka = 6.3 x 10-5 mol dm-3

  • HCOOH Ka = 1.8 x 10-4 mol dm-3

  • HCN Ka = 4.9 x 10-10 mol dm-3

  • CH3CH2COOH Ka = 1.4 x 10-5 mol dm-3

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3
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The pKb value of ethylamine is 3.35 at 298 K. What is the value of the pKa ethylammonium ion?

  • fraction numerator 10 to the power of negative 14 end exponent over denominator 3.35 end fraction

  • 14 - 3.35

  • begin mathsize 14px style fraction numerator 14 over denominator 3.35 end fraction end style

  • begin mathsize 14px style 10 to the power of blank to the power of negative 14 end exponent end exponent over 10 to the power of negative 3.35 end exponent end style

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4
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Which of the following is the correct equation to calculate the concentration of hydroxide ions? 

  • K subscript straight w over pOH

  • -log [H+]

  • 14 - pOH

  • 10-pOH

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5
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Which shows the correct relationship between Kw, Ka and Kb? 

  • Kw = Ka + Kb

  • Kw = Ka Kb

  • K subscript w space equals space K subscript a over K subscript b

  • K subscript w space equals space K subscript b over K subscript a

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11 mark

The table shows the pKa and Ka values for four acids

Acid

pKa

Ka

Butanoic Acid

-

1.51 x 10-5

Nitrous acid

3.1

-

Lactic acid

3.4

-

Phenol

-

1 x 10-10

  

Which of the following is the correct order of increasing strength of the acids

  • Phenol < butanoic acid < lactic acid < nitrous acid 

  • Nitrous acid < lactic acid < butanoic acid < phenol

  • Nitrous acid < butanoic acid < phenol < lactic acid

  • Phenol < lactic acid < butanoic acid < nitrous acid

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21 mark

Which of the following statements is correct? 

  • As temperature increases, the pH value of pure water decreases

  • As temperature decreases, the pH value of pure water decreases

  • The pH of water is unaffected by temperature 

  • Pure water is not neutral 

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31 mark

Which of the following statements about conjugate acid and base pairs are correct?

I.
If an acid has a pKa value of 4, its conjugate base will have a pKb value of 10
II.
Ka + Kb = Kw
III.

The conjugate base for ethanoic acid is CH3COO-

  • I and II only

  • I and III only

  • II and III only

  • I, II and III

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41 mark

What is the correct expression to use to determine the pH of butanoic acid with concentration of 0.75 mol dm-3? 

The Ka of butanoic acid at 298 K is 1.51 x 10-5 mol dm-3

  • -log10 (begin mathsize 14px style 1.51 cross times 10 to the power of negative 5 end exponent cross times 0.75 end style)

  • -log10begin mathsize 14px style square root of left parenthesis 1.51 cross times 10 to the power of negative 5 end exponent cross times 0.75 right parenthesis end root end style

  • -log10 0.75

  • begin mathsize 14px style fraction numerator 0.75 over denominator 1.51 cross times 10 to the power of negative 5 end exponent end fraction end style

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51 mark

What is the correct expression for the base dissociation constant, Kb, for propylamine?

  • Kb = begin mathsize 14px style fraction numerator left square bracket C H subscript 3 C H subscript 2 C H subscript 2 N H subscript 3 to the power of plus right square bracket open square brackets O H to the power of minus sign close square brackets over denominator open square brackets C H subscript 3 C H subscript 2 C H subscript 2 N H subscript 2 close square brackets end fraction end style

  • Kb = begin mathsize 14px style fraction numerator left square bracket C H subscript 3 C H subscript 2 C H subscript 2 N H subscript 3 to the power of plus right square bracket open square brackets H subscript 2 O close square brackets over denominator open square brackets C H subscript 3 C H subscript 2 C H subscript 2 N H subscript 2 close square brackets end fraction end style

  • Kb = begin mathsize 14px style fraction numerator left square bracket C H subscript 3 C H subscript 2 C H subscript 2 N H subscript 3 to the power of plus right square bracket open square brackets O H to the power of minus sign close square brackets over denominator open square brackets C H subscript 3 C H subscript 2 C H subscript 2 N H subscript 2 close square brackets open square brackets H subscript 2 O close square brackets end fraction end style

  • Kb = begin mathsize 14px style left square bracket C H subscript 3 C H subscript 2 C H subscript 2 N H subscript 3 to the power of plus right square bracket open square brackets O H to the power of minus sign close square brackets end style

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1
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The table below shows data for the and values for some acids and bases at 298 K.

Acid Ka Base pKb
C5H6OH 1.02 x 10-10 (C2H5)3N 3.25
O2NC6H4OH 7.08 x 10-8 C6H5NH2 9.13

Which two formulas represent the weakest acid and the weakest base in the table?

  • C5H6OH and C6H5NH2

  • O2NC6H4OH and C6H5NH2

  • O2NC6H4OH and (C2H5)3N

  • C5H6OH and (C2H5)3N

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2
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The ionisation constant of water, Kw , at 40 °C is 2.92 x 10-14. Which of the following statements is correct?

  • pH = 7.0

  • The ionisation of water is exothermic

  • The pH of water is lower at 40 °C than at 25 °C

  • [H+] > [OH-] at 40 °C

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3
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The Kb value for a base is 8.0 x 10-4 at 298 K. What is the pKa value for the conjugate acid at this temperature? 

  • 10

  • 1.3 x 10-11

  • 3.1

  • 10.9

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4
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The pKb value of HPO42- is 6.8. What is its conjugate acid and what is the Ka value?

  Conjugate acid Ka
A. H2PO4- 7.2
B. H3PO4 7.2
C H3PO4 1.67 x 10-7
D. H2PO4- 6.3 x 10-8

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    5
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    The strengths of four bases are:

    • Phenylamine pKb = 9.13
    • Ethylamine Kb = 4.46 x 10-4
    • 3-Nitrophenol pKb = 8.36
    • Ethanol Kb = 3.16 x 10-16

    What is the order of increasing base strength?

    • Ethanol < phenylamine < 3-nitrophenol < ethylamine 

    • Ethanol < 3-nitrophenol < phenylamine < ethylamine 

    • Ethylamine < 3-nitrophenol < phenylamine < ethanol

    • Ethylamine < phenylamine < 3-nitrophenol < ethanol

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