Worksheet: Concentrations from Ionization Constants

In this worksheet, we will practice using dissociation constants to find the equilibrium concentrations of undissociated acids and bases.

Q1:

Acetic acid is the principal ingredient in vinegar. In a sample of vinegar at equilibrium, [CHCOH]=0.0787M32 and [HO]=[CHCO]=0.00118M3+32. What is the value of 𝐾a for acetic acid?

  • A1.39×10
  • B1.77×10
  • C5.65×10
  • D1.10×10
  • E1.18×10

Q2:

What is the hydronium ion concentration in a 0.100 M solution of ammonium nitrate, NHNO43, a salt composed of the ions NH4+ and NO3? 𝐾b of ammonia is 1.8×10.

  • A2.3×10 M
  • B1.0×10 M
  • C7.5×10 M
  • D4.3×10 M
  • E5.6×10 M

Q3:

Caffeine, CHNO81042, is a weak base. What is the value of 𝐾b for caffeine if a solution at equilibrium has [CHNO]=M810420.050, [CHNOH]=M81042+5.0×10, and [OH]=M2.5×10?

  • A1.3×10
  • B2.5×10
  • C1.3×10
  • D2.5×10

Q4:

Consider the equilibrium for the ionization of trimethylamine, a weak base. (CH)N()+HO()(CH)NH()+OH()33233+aqlaqaq

The 𝐾b of trimethylamine is 6.3×10. Assuming the effect of dissociation on the trimethylamine concentration is negligible, calculate the concentration of hydroxide ions in a 0.25 M trimethylamine solution.

  • A1.9×10 M
  • B4.0×10 M
  • C2.5×10 M
  • D5.1×10 M
  • E3.8×10 M

Q5:

Consider the following equilibrium. CHCO()+HO()CHCOH()+OH()32232aqlaqaq

What is the equilibrium acetic acid concentration in a solution where [CHCO]=0.050M32 and [OH]=M2.5×10 at equilibrium? The 𝐾a of acetic acid is 1.8×10.

  • A7.1×10 M
  • B6.9×10 M
  • C1.1×10 M
  • D2.5×10 M
  • E1.8×10 M

Q6:

When Al(NO)33 dissolves in water, [Al(HO)]263+ ions are formed. The [Al(HO)]263+ ion acts as a monoprotic acid with a 𝐾a value of 1.4×10. Calculate the concentration of [Al(HO)(OH)]252+ ions in a 0.15 M solution of Al(NO)33 if the concentration of HO3+ ions is 0.10 M.

  • A4.4×10 M
  • B3.1×10 M
  • C2.1×10 M
  • D4.2×10 M
  • E9.8×10 M

Q7:

When dealing with acid and base solutions, when is it necessary to use equilibrium calculations to accurately determine equilibrium concentrations?

  • AIn nonaqueous systems
  • BWhen the temperature is not 25C
  • COnly at very low concentrations
  • DWhen a strong acid or base is involved
  • EWhen a weak acid or base is involved

Q8:

In an aqueous solution at equilibrium, [OH]=M4.38×10, [NH]=M4+4.38×10 and [NH]=1.066M3. Calculate the value of 𝐾b for NH3.

  • A1.80×10
  • B5.56×10
  • C4.11×10
  • D2.43×10
  • E1.07

Q9:

In a hypochlorous acid (HClO) solution at equilibrium, [OH]=M4.0×10, [HClO]=M2.38×10 and [ClO]=M3.33×10. Calculate to 3 significant figures the value of 𝐾b for ClO.

  • A6.00×10
  • B3.17×10
  • C5.03×10
  • D3.50×10
  • E2.86×10

Q10:

In a solution of acetic acid (CHCOH)32 at equilibrium, [HO]=M3+1.90×10, [CHCO]=M321.90×10, and [CHCOH]=0.198M32. What is the value of 𝐾a for CHCOH32?

  • A1.04×10
  • B1.82×10
  • C9.60×10
  • D7.15×10
  • E5.48×10

Q11:

Using the equilibrium concentrations [NH]=0.10M,+4[NH]=M,37.5×10 and [HO]=M,3+7.5×10 what is the value of 𝐾a for NH+4?

  • A1.8×10
  • B5.6×10
  • C1.3×10
  • D0.10
  • E8.0×10

Q12:

Using the equilibrium concentrations [HO]=0.0156M3+,

[NO]=0.0619M2,

and [HNO]=2.14M2,

what is the value of 𝐾a for HNO2?

  • A6.01×10
  • B4.84×10
  • C2.07×10
  • D4.51×10
  • E2.22×10

Q13:

For which of the following solutions must we consider the ionization of water when calculating the pH or pOH?

  • A2 M  HSO24
  • B0.00080 g  NaOH in 0.10 L of solution
  • C1×10 M  Ca(OH)2
  • D3×10 M  HNO3
  • E0.10 g  HCl in 1.0 L of solution

Q14:

A 0.134 M solution of the diprotic acid HCO23 contains HO3+, OH, HCO23, HCO3, and CO32. Which two of these species are present in almost equal concentrations?

  • A[HO]3+ and [OH]
  • B[HCO]23 and [HCO]3
  • C[HO]3+ and [HCO]3
  • D[OH] and [HCO]3
  • E[CO]32 and [OH]

Q15:

What is the concentration of ClO in a 0.0092 M aqueous solution of hypochlorous acid (HClO) at 25C? The 𝐾a of hypochlorous acid is 2.9×10.

  • A0.0092 M
  • B5.8×10 M
  • C9.1×10 M
  • D1.6×10 M
  • E6.1×10 M

Q16:

What is the concentration of Fe(HO)OH25+ in 0.120 MFe(HO)262+ at 25C? 𝐾a of Fe(HO)262+ is 1.6×10.

  • A7.2×10 M
  • B1.4×10 M
  • C1.9×10 M
  • D1.2×10 M
  • E1.2×10 M

Q17:

What is the concentration of CN in 0.0810 MHCN at 25C? 𝐾a of HCN is 4.9×10.

  • A1.6×10 M
  • B3.1×10 M
  • C7.9×10 M
  • D0.081 M
  • E6.3×10 M

Q18:

What is the concentration of CHNH653+ in 0.0784 MCHNH652 at 25C? 𝐾b of CHNH652 is 4.3×10.

  • A0.078 M
  • B1.7×10 M
  • C4.3×10 M
  • D4.4×10 M
  • E5.8×10 M

Q19:

What is the concentration of (CH)NH33+ in 0.11 M(CH)N33 at 25C? 𝐾b of (CH)N33 is 6.3×10.

  • A3.8×10 M
  • B2.6×10 M
  • C5.6×10 M
  • D1.1×10 M
  • E5.3×10 M

Q20:

In a trimethylamine ((CH)N)33 solution at equilibrium, [(CH)N]=M330.29, [(CH)NH]=M33+4.3×10, and [OH]=M4.3×10. Calculate the value of 𝐾b for trimethylamine.

  • A7.1×10
  • B5.9×10
  • C0.29
  • D6.4×10
  • E1.6×10

Q21:

Propionic acid, CHCOH252 (𝐾=1.34×10a) is used in the manufacture of calcium propionate, a food preservative. Calculate to 2 significant figures the hydronium ion concentration in a 0.712 M solution of CHCOH252.

  • A9.5×10 M
  • B3.1×10 M
  • C7.1×10 M
  • D1.9×10 M
  • E4.3×10 M

Q22:

The ionization constant of lactic acid, CHCH(OH)COH32, an acid found in blood after strenuous exercise, is 1.36×10. If 15.0 g of lactic acid is used to make a solution with a volume of 1.00 L, what is the concentration of hydronium ions in the solution?

  • A4.76×10 M
  • B2.26×10 M
  • C4.69×10 M
  • D8.17×10 M
  • E2.86×10 M

Q23:

A 1.00 L stock solution is prepared by dissolving 1.00 mole of a monoprotic acid in water. The 𝐾a value of the acid is 0.050. When calculating [H]+ at equilibrium, a student assumes that the change in concentration of the undissociated acid is negligible. Calculate to 2 significant figures the percentage error in the calculated value of [H]+ relative to the true value.

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