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?

  • A 1 . 3 9 × 1 0
  • B 1 . 7 7 × 1 0
  • C 5 . 6 5 × 1 0
  • D 1 . 1 0 × 1 0
  • E 1 . 1 8 × 1 0

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.

  • A 2 . 3 × 1 0 M
  • B 1 . 0 × 1 0 M
  • C 7 . 5 × 1 0 M
  • D 4 . 3 × 1 0 M
  • E 5 . 6 × 1 0 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?

  • A 1 . 3 × 1 0
  • B 2 . 5 × 1 0
  • C 1 . 3 × 1 0
  • D 2 . 5 × 1 0

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.

  • A 1 . 9 × 1 0 M
  • B 4 . 0 × 1 0 M
  • C 2 . 5 × 1 0 M
  • D 5 . 1 × 1 0 M
  • E 3 . 8 × 1 0 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.

  • A 7 . 1 × 1 0 M
  • B 6 . 9 × 1 0 M
  • C 1 . 1 × 1 0 M
  • D 2 . 5 × 1 0 M
  • E 1 . 8 × 1 0 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.

  • A 4 . 4 × 1 0 M
  • B 3 . 1 × 1 0 M
  • C 2 . 1 × 1 0 M
  • D 4 . 2 × 1 0 M
  • E 9 . 8 × 1 0 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.

  • A 1 . 8 0 × 1 0
  • B 5 . 5 6 × 1 0
  • C 4 . 1 1 × 1 0
  • D 2 . 4 3 × 1 0
  • 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.

  • A 6 . 0 0 × 1 0
  • B 3 . 1 7 × 1 0
  • C 5 . 0 3 × 1 0
  • D 3 . 5 0 × 1 0
  • E 2 . 8 6 × 1 0

Q10:

In a solution of acetic acid (CHCOH)32 at equilibrium, [HO]=M3+1.90×10, [CHCO]=M321.90×10, and [CHCOH]=M320.198. What is the value of 𝐾a for CHCOH32?

  • A 1 . 0 4 × 1 0
  • B 1 . 8 2 × 1 0
  • C 9 . 6 0 × 1 0
  • D 7 . 1 5 × 1 0
  • E 5 . 4 8 × 1 0

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?

  • A 1 . 8 × 1 0
  • B 5 . 6 × 1 0
  • C 1 . 3 × 1 0
  • D0.10
  • E 8 . 0 × 1 0

Q12:

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

[ N O ] = 0 . 0 6 1 9 M 2 ,

and [HNO]=2.14M2,

what is the value of 𝐾a for HNO2?

  • A 6 . 0 1 × 1 0
  • B 4 . 8 4 × 1 0
  • C 2 . 0 7 × 1 0
  • D 4 . 5 1 × 1 0
  • E 2 . 2 2 × 1 0

Q13:

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

  • A 0 . 1 0 g H C l in 1.0 L of solution
  • B 0 . 0 0 0 8 0 g N a O H in 0.10 L of solution
  • C 2 M H S O 2 4
  • D 1 × 1 0 M C a ( O H ) 2
  • E 3 × 1 0 M H N O 3

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 [ H O ] 3 + and [OH]
  • B [ H C O ] 2 3 and [HCO]3
  • C [ H O ] 3 + and [HCO]3
  • D [ O H ] and [HCO]3
  • E [ C O ] 3 2 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
  • B 5 . 8 × 1 0 M
  • C 9 . 1 × 1 0 M
  • D 1 . 6 × 1 0 M
  • E 6 . 1 × 1 0 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.

  • A 7 . 2 × 1 0 M
  • B 1 . 4 × 1 0 M
  • C 1 . 9 × 1 0 M
  • D 1 . 2 × 1 0 M
  • E 1 . 2 × 1 0 M

Q17:

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

  • A 1 . 6 × 1 0 M
  • B 3 . 1 × 1 0 M
  • C 7 . 9 × 1 0 M
  • D0.081 M
  • E 6 . 3 × 1 0 M

Q18:

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

  • A0.078 M
  • B 1 . 7 × 1 0 M
  • C 4 . 3 × 1 0 M
  • D 4 . 4 × 1 0 M
  • E 5 . 8 × 1 0 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.

  • A 3 . 8 × 1 0 M
  • B 2 . 6 × 1 0 M
  • C 5 . 6 × 1 0 M
  • D 1 . 1 × 1 0 M
  • E 5 . 3 × 1 0 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.

  • A 7 . 1 × 1 0
  • B 5 . 9 × 1 0
  • C0.29
  • D 6 . 4 × 1 0
  • E 1 . 6 × 1 0

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.

  • A 9 . 5 × 1 0 M
  • B 3 . 1 × 1 0 M
  • C 7 . 1 × 1 0 M
  • D 1 . 9 × 1 0 M
  • E 4 . 3 × 1 0 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?

  • A 4 . 7 6 × 1 0 M
  • B 2 . 2 6 × 1 0 M
  • C 4 . 6 9 × 1 0 M
  • D 8 . 1 7 × 1 0 M
  • E 2 . 8 6 × 1 0 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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