Ionization Constants Acids Acid Formula Ionization Constant K a Acetic CH 3 COOH

Question

Ionization Constants

Acids

Acid

Formula

Ionization Constant Ka

Acetic

CH3COOH

1.8×10–5

Arsenic

H3AsO4

5.5×10–3

Benzoic

C6H5COOH

6.3×10–5

Boric

H3BO3

5.4×10–10

Butanoic

C3H7COOH

1.5×10–5

Carbonic

H2CO3

Ka1 = 4.5×10–7
Ka2 = 4.7×10–11

Chloroacetic

ClCH2COOH

1.4×10–3

Chlorous

HClO2

1.1×10–2

Chromic

H2CrO4

Ka1 = 1.8×10–1
Ka2 = 3.2×10–7

Cyanic

HCNO

3.5×10–4

Formic

HCOOH

1.8×10–4

Hydrazoic

HN3

2.5×10–5

Hydrocyanic

HCN

6.2×10–10

Hydrofluoric

HF

6.3×10–4

Hydrogen peroxide

H2O2

2.4×10–12

Hydrosulfuric

H2S

Ka1 = 8.9×10–8
Ka2 = 1.0×10–19

Hypobromous

HBrO

2.8×10–9

Hypochlorous

HClO

4.0×10–8

Hypoiodous

HIO

3.2×10–11

Iodic

HIO3

1.7×10–1

Nitrous

HNO2

5.6×10–4

Oxalic

C2H2O4

Ka1 = 5.6×10–2
Ka2 = 1.5×10–4

Paraperiodic

H5IO6

2.8×10–2

Pentanoic

C4H9COOH

1.5×10–5

Periodic

HIO4

7.3×10–2

Phenol

HC6H5O

1.3×10–10

Phosphoric

H3PO4

Ka1 = 6.9×10–3
Ka2 = 6.2×10–8
Ka3 = 4.8×10–13

Phosphorous

H3PO3

Ka1 = 5.0×10–2
Ka2 = 2.0×10–7

Propanoic

C2H5COOH

1.3×10–5

Sulfuric

H2SO4

Ka1 = very large
Ka2 = 1.2×10–2

Sulfurous

H2SO3

Ka1 = 1.4×10–2
Ka2 = 6.3×10–8

Trichloroacetic

Cl3CCOOH

2.2×10–1

Bases

Base

Formula

Ionization Constant Kb

Ammonia

NH3

1.8×10–5

Methylamine

CH3NH2

5.0×10–4

Dimethylamine

(CH3)2NH

5.4×10–4

Diethylamine

(C2H5)2NH

6.9×10–4

Trimethylamine

(CH3)3N

6.3×10–5

Triethylamine

(C2H5)3N

5.6×10–4

Ethylamine

CH3CH2NH2

6.3×10–4

Ethylenediamine

(CH2NH2)2

8.3×10–5

Pyridine

C5H5N

1.7×10–9

Hydroxylamine

NH2OH

8.7×10–9

Aniline

C6H5NH2

7.4×10–10

Hydrazine

H2NNH2

1.3×10–6

Ionization Constants

Acids

Acid

Formula

Ionization Constant Ka

Acetic

CH3COOH

1.8×10–5

Arsenic

H3AsO4

5.5×10–3

Benzoic

C6H5COOH

6.3×10–5

Boric

H3BO3

5.4×10–10

Butanoic

C3H7COOH

1.5×10–5

Carbonic

H2CO3

Ka1 = 4.5×10–7
Ka2 = 4.7×10–11

Chloroacetic

ClCH2COOH

1.4×10–3

Chlorous

HClO2

1.1×10–2

Chromic

H2CrO4

Ka1 = 1.8×10–1
Ka2 = 3.2×10–7

Cyanic

HCNO

3.5×10–4

Formic

HCOOH

1.8×10–4

Hydrazoic

HN3

2.5×10–5

Hydrocyanic

HCN

6.2×10–10

Hydrofluoric

HF

6.3×10–4

Hydrogen peroxide

H2O2

2.4×10–12

Hydrosulfuric

H2S

Ka1 = 8.9×10–8
Ka2 = 1.0×10–19

Hypobromous

HBrO

2.8×10–9

Hypochlorous

HClO

4.0×10–8

Hypoiodous

HIO

3.2×10–11

Iodic

HIO3

1.7×10–1

Nitrous

HNO2

5.6×10–4

Oxalic

C2H2O4

Ka1 = 5.6×10–2
Ka2 = 1.5×10–4

Paraperiodic

H5IO6

2.8×10–2

Pentanoic

C4H9COOH

1.5×10–5

Periodic

HIO4

7.3×10–2

Phenol

HC6H5O

1.3×10–10

Phosphoric

H3PO4

Ka1 = 6.9×10–3
Ka2 = 6.2×10–8
Ka3 = 4.8×10–13

Phosphorous

H3PO3

Ka1 = 5.0×10–2
Ka2 = 2.0×10–7

Propanoic

C2H5COOH

1.3×10–5

Sulfuric

H2SO4

Ka1 = very large
Ka2 = 1.2×10–2

Sulfurous

H2SO3

Ka1 = 1.4×10–2
Ka2 = 6.3×10–8

Trichloroacetic

Cl3CCOOH

2.2×10–1

Bases

Base

Formula

Ionization Constant Kb

Ammonia

NH3

1.8×10–5

Methylamine

CH3NH2

5.0×10–4

Dimethylamine

(CH3)2NH

5.4×10–4

Diethylamine

(C2H5)2NH

6.9×10–4

Trimethylamine

(CH3)3N

6.3×10–5

Triethylamine

(C2H5)3N

5.6×10–4

Ethylamine

CH3CH2NH2

6.3×10–4

Ethylenediamine

(CH2NH2)2

8.3×10–5

Pyridine

C5H5N

1.7×10–9

Hydroxylamine

NH2OH

8.7×10–9

Aniline

C6H5NH2

7.4×10–10

Hydrazine

H2NNH2

1.3×10–6

Acids

Acid

Formula

Ionization Constant Ka

Acetic

CH3COOH

1.8×10–5

Arsenic

H3AsO4

5.5×10–3

Benzoic

C6H5COOH

6.3×10–5

Boric

H3BO3

5.4×10–10

Butanoic

C3H7COOH

1.5×10–5

Carbonic

H2CO3

Ka1 = 4.5×10–7
Ka2 = 4.7×10–11

Chloroacetic

ClCH2COOH

1.4×10–3

Chlorous

HClO2

1.1×10–2

Chromic

H2CrO4

Ka1 = 1.8×10–1
Ka2 = 3.2×10–7

Cyanic

HCNO

3.5×10–4

Formic

HCOOH

1.8×10–4

Hydrazoic

HN3

2.5×10–5

Hydrocyanic

HCN

6.2×10–10

Hydrofluoric

HF

6.3×10–4

Hydrogen peroxide

H2O2

2.4×10–12

Hydrosulfuric

H2S

Ka1 = 8.9×10–8
Ka2 = 1.0×10–19

Hypobromous

HBrO

2.8×10–9

Hypochlorous

HClO

4.0×10–8

Hypoiodous

HIO

3.2×10–11

Iodic

HIO3

1.7×10–1

Nitrous

HNO2

5.6×10–4

Oxalic

C2H2O4

Ka1 = 5.6×10–2
Ka2 = 1.5×10–4

Paraperiodic

H5IO6

2.8×10–2

Pentanoic

C4H9COOH

1.5×10–5

Periodic

HIO4

7.3×10–2

Phenol

HC6H5O

1.3×10–10

Phosphoric

H3PO4

Ka1 = 6.9×10–3
Ka2 = 6.2×10–8
Ka3 = 4.8×10–13

Phosphorous

H3PO3

Ka1 = 5.0×10–2
Ka2 = 2.0×10–7

Propanoic

C2H5COOH

1.3×10–5

Sulfuric

H2SO4

Ka1 = very large
Ka2 = 1.2×10–2

Sulfurous

H2SO3

Ka1 = 1.4×10–2
Ka2 = 6.3×10–8

Trichloroacetic

Cl3CCOOH

2.2×10–1

Calculate the change in pH when 6.00 mL of 0.100 M HCI(aq) is added to 100.0 mL of a buffer solution that is 0.100 M in NH3(aq) and 0.100 M in NH4CI(aq). A list of ionization constants can be found here. Number Calculate the change in pH when 6.00 mL of 0.100 M NaOH(aq) is added to the original buffer solution. Number

Explanation / Answer

Volume of Buffer = 100 mL = 0.1 L

[NH3] = [NH4Cl] = 0.1 M

Moles = Molarity x Volume (L)

=> Moles of NH3 = 0.1 x 0.1 = 0.01

Moles of NH4Cl = 0.1 x 0.1 = 0.01

1)

Moles of HCl added = 0.1 x 0.006 = 0.0006 moles

Kb for NH3 = 1.8 x 10^-5

pKb = - log Kb

=> pKb = 4.745

pOH for the above buffer before adding HCl

pOH = pKb + log (NH4Cl / NH3)

=> pOH = 4.745 + log (0.01 / 0.01) = 4.745

pH = 14 - pOH = 9.255

pOH after adding HCl

pOH = pKb + log (NH4Cl + HCl / NH3 - HCl)

=> pOH = 4.745 + log (0.01 + 0.0006 / 0.01 - 0.0006) = 4.797

pH = 9.203

delta pH = 9.203 - 9.255 = - 0.052

2)

Moles of NaOH added = 0.1 x 0.006 = 0.0006 moles

Kb for NH3 = 1.8 x 10^-5

pKb = - log Kb

=> pKb = 4.745

pOH for the above buffer before adding NaOH

pOH = pKb + log (NH4Cl / NH3)

=> pOH = 4.745 + log (0.01 / 0.01) = 4.745

pH = 14 - pOH = 9.255

pOH after adding NaOH

pOH = pKb + log (NH4Cl - NaOH / NH3 + NaOH)

=> pOH = 4.745 + log (0.01 - 0.0006 / 0.01 + 0.0006) = 4.693

pH = 9.307

delta pH = 9.307 - 9.255 = 0.052

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