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Worksheet: Concentrations from Ionization Constants

Q1:

Consider the equilibrium for the ionization of trimethylamine, a weak base:

The 𝐾 b of trimethylamine is 6 . 3 Γ— 1 0 βˆ’ 5 . 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 Γ— 1 0 βˆ’ 2 M
  • B 3 . 8 Γ— 1 0 βˆ’ 2 M
  • C 2 . 5 Γ— 1 0 βˆ’ 3 M
  • D 4 . 0 Γ— 1 0 βˆ’ 3 M
  • E 5 . 1 Γ— 1 0 βˆ’ 2 M

Q2:

What is the concentration of F e ( H O ) O H 2 5 + in 0 . 1 2 0 M F e ( H O ) 2 6 2 + at 2 5 ∘ C ? 𝐾 a of F e ( H O ) 2 6 2 + is 1 . 6 Γ— 1 0 βˆ’ 7 .

  • A 7 . 2 Γ— 1 0 βˆ’ 1 1 M
  • B 0.12 M
  • C 1 . 9 Γ— 1 0 βˆ’ 4 M
  • D 1 . 4 Γ— 1 0 βˆ’ 4 M
  • E 1 . 2 Γ— 1 0 βˆ’ 3 M

Q3:

A 0.134 M solution of the diprotic acid H C O 2 3 contains H O 3 + , O H , H C O , H C O , a n d C O – 2 3 3 – 3 2 – . Which two of these species are present in almost equal concentrations?

  • A [ H C O ] , [ H C O ] 2 3 3 –
  • B [ H O ] , [ O H ] 3 + –
  • C [ O H ] , [ H C O ] – 3 –
  • D [ H O ] , [ H C O ] 3 + 3 –
  • E [ C O ] , [ O H ] 3 2 – –

Q4:

What is the hydronium ion concentration in a 0.100 M solution of ammonium nitrate, N H N O 4 3 , a salt composed of the ions N H 4 + and N O 3 – ? 𝐾 b of ammonia is 1 . 8 Γ— 1 0   .

  • A 1 . 0 Γ— 1 0   οŠͺ M
  • B 2 . 3 Γ— 1 0   M
  • C 4 . 3 Γ— 1 0    M
  • D 7 . 5 Γ— 1 0   M
  • E 5 . 6 Γ— 1 0    M

Q5:

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 1 Γ— 1 0 βˆ’ 4 M C a ( O H ) 2
  • C 0 . 0 0 0 8 0 g N a O H in 0.10 L of solution
  • D 3 Γ— 1 0 βˆ’ 8 M H N O 3
  • E 2 M H S O 2 4

Q6:

Acetic acid is the principal ingredient in vinegar. In a sample of vinegar at equilibrium, [ C H C O H ] = 0 . 0 7 8 7 M 3 2 and [ H O ] = [ C H C O ] = 0 . 0 0 1 1 8 M 3 + 3 2 – . What is the value of 𝐾 a for acetic acid?

  • A 1 . 1 0 Γ— 1 0 βˆ’ 7
  • B 5 . 6 5 Γ— 1 0 βˆ’ 4
  • C 1 . 3 9 Γ— 1 0 βˆ’ 6
  • D 1 . 7 7 Γ— 1 0 βˆ’ 5
  • E 1 . 1 8 Γ— 1 0 βˆ’ 3

Q7:

In a hypochlorous acid ( H C l O ) solution at equilibrium, [ O H ] M – = 4 . 0 Γ— 1 0 βˆ’ 6 , [ H C l O ] M = 2 . 3 8 Γ— 1 0 βˆ’ 5 and [ C l O ] M – = 3 . 3 3 Γ— 1 0 βˆ’ 4 . Calculate to 3 significant figures the value of 𝐾 b for C l O – .

  • A 3 . 5 0 Γ— 1 0 βˆ’ 6
  • B 3 . 1 7 Γ— 1 0 βˆ’ 1 4
  • C 5 . 0 3 Γ— 1 0 βˆ’ 8
  • D 2 . 8 6 Γ— 1 0 βˆ’ 7
  • E 6 . 0 0 Γ— 1 0 βˆ’ 1 0

Q8:

The ionization constant of lactic acid, C H C H ( O H ) C O H 3 2 , an acid found in blood after strenuous exercise, is 1 . 3 6 Γ— 1 0  οŠͺ . 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 2 . 2 6 Γ— 1 0   M
  • B 2 . 8 6 Γ— 1 0   M
  • C 8 . 1 7 Γ— 1 0  οŠͺ M
  • D 4 . 6 9 Γ— 1 0   M
  • E 4 . 7 6 Γ— 1 0   M

Q9:

When A l ( N O ) 3 3 dissolves in water, [ A l ( H O ) ] 2 6 3 + ions are formed. The [ A l ( H O ) ] 2 6 3 + ion acts as a monoprotic acid with a 𝐾 a value of 1 . 4 Γ— 1 0 βˆ’ 5 . Calculate the concentration of [ A l ( H O ) ( O H ) ] 2 5 2 + ions in a 0.15 M solution of A l ( N O ) 3 3 if the concentration of H O 3 + ions is 0.10 M.

  • A 3 . 1 Γ— 1 0 βˆ’ 5 M
  • B 4 . 2 Γ— 1 0 βˆ’ 5 M
  • C 9 . 8 Γ— 1 0 βˆ’ 6 M
  • D 2 . 1 Γ— 1 0 βˆ’ 5 M
  • E 4 . 4 Γ— 1 0 βˆ’ 6 M

Q10:

Using the equilibrium concentrations [ N H ] M 4 + = 0 . 1 0 , [ N H ] M 3 = 7 . 5 Γ— 1 0 ,   and [ H O ] M 3 + = 7 . 5 Γ— 1 0 ,   what is the value of 𝐾 a for N H 4 + ?

  • A 1 . 8 Γ— 1 0  
  • B0.10
  • C 8 . 0 Γ— 1 0  
  • D 5 . 6 Γ— 1 0   
  • E 1 . 3 Γ— 1 0   

Q11:

Propionic acid, C H C O H 2 5 2 ( 𝐾 = 1 . 3 4 Γ— 1 0 a βˆ’ 5 ) 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 C H C O H 2 5 2 .

  • A 9 . 5 Γ— 1 0 βˆ’ 6 M
  • B 4 . 3 Γ— 1 0 βˆ’ 3 M
  • C 7 . 1 Γ— 1 0 βˆ’ 5 M
  • D 3 . 1 Γ— 1 0 βˆ’ 3 M
  • E 1 . 9 Γ— 1 0 βˆ’ 5 M

Q12:

Using the equilibrium concentrations

[ H O ] M 3 + = 0 . 0 1 5 6 ,

[ N O ] M 2 – = 0 . 0 6 1 9 ,

and [ H N O ] M 2 = 2 . 1 4 ,

what is the value of 𝐾 a for H N O 2 ?

  • A 4 . 8 4 Γ— 1 0 
  • B 2 . 2 2 Γ— 1 0 
  • C 2 . 0 7 Γ— 1 0  
  • D 4 . 5 1 Γ— 1 0  οŠͺ
  • E 6 . 0 1 Γ— 1 0  

Q13:

In a trimethylamine ( ( C H ) N ) 3 3 solution at equilibrium, [ ( C H ) N ] = 0 . 2 9 M , [ ( C H ) N H ] M 3 3 3 3 + = 4 . 3 Γ— 1 0 βˆ’ 3 and [ O H ] M – = 4 . 3 Γ— 1 0 βˆ’ 3 . Calculate the value of 𝐾 b for trimethylamine.

  • A 1 . 6 Γ— 1 0 4
  • B0.29
  • C 5 . 9 Γ— 1 0 βˆ’ 3
  • D 6 . 4 Γ— 1 0 βˆ’ 5
  • E 7 . 1 Γ— 1 0 βˆ’ 8

Q14:

What is the concentration of C H N H 6 5 3 + in 0 . 0 7 8 4 M C H N H 6 5 2 at 2 5 ∘ C ? 𝐾 b of C H N H 6 5 2 is 4 . 3 Γ— 1 0 βˆ’ 1 0 .

  • A 0.078 M
  • B 1 . 7 Γ— 1 0 βˆ’ 9 M
  • C 4 . 4 Γ— 1 0 βˆ’ 4 M
  • D 5 . 8 Γ— 1 0 βˆ’ 6 M
  • E 4 . 3 Γ— 1 0 βˆ’ 1 0 M

Q15:

What is the concentration of C l O – in a 0.0092 M aqueous solution of hypochlorous acid ( H C l O ) at 2 5 ∘ C ? The 𝐾 a of hypochlorous acid is 2 . 9 Γ— 1 0 βˆ’ 8 .

  • A 0.0092 M
  • B 6 . 1 Γ— 1 0 βˆ’ 1 0 M
  • C 5 . 8 Γ— 1 0 βˆ’ 5 M
  • D 1 . 6 Γ— 1 0 βˆ’ 5 M
  • E 9 . 1 Γ— 1 0 βˆ’ 7 M

Q16:

What is the concentration of ( C H ) N H 3 3 + in 0 . 1 1 M ( C H ) N 3 3 at 2 5 ∘ C ? The 𝐾 b of ( C H ) N 3 3 is 6 . 3 Γ— 1 0 βˆ’ 5 .

  • A 5 . 6 Γ— 1 0 βˆ’ 8 M
  • B 3 . 8 Γ— 1 0 βˆ’ 1 2 M
  • C 1 . 1 Γ— 1 0 βˆ’ 3 M
  • D 2 . 6 Γ— 1 0 βˆ’ 3 M
  • E 5 . 3 Γ— 1 0 βˆ’ 5 M

Q17:

What is the concentration of C N – in 0 . 0 8 1 0 M H C N at 2 5 ∘ C ? 𝐾 a of H C N is 4 . 9 Γ— 1 0 βˆ’ 1 0 .

  • A 1 . 6 Γ— 1 0 βˆ’ 9 M
  • B 0.081 M
  • C 3 . 1 Γ— 1 0 βˆ’ 8 M
  • D 6 . 3 Γ— 1 0 βˆ’ 6 M
  • E 7 . 9 Γ— 1 0 βˆ’ 3 M

Q18:

Consider the equilibrium

What is the equilibrium acetic acid concentration in a solution where [ C H C O ] M 3 2 – = 0 . 0 5 0 and [ O H ] M – = 2 . 5 Γ— 1 0 βˆ’ 6 at equilibrium? The 𝐾 a of acetic acid is 1 . 8 Γ— 1 0 βˆ’ 5 .

  • A 6 . 9 Γ— 1 0 βˆ’ 3 M
  • B 1 . 8 Γ— 1 0 βˆ’ 5 M
  • C 2 . 5 Γ— 1 0 βˆ’ 6 M
  • D 1 . 1 Γ— 1 0 βˆ’ 5 M
  • E 7 . 1 Γ— 1 0 βˆ’ 8 M

Q19:

Caffeine, C H N O 8 1 0 4 2 , is a weak base. What is the value of 𝐾 b for caffeine if a solution at equilibrium has [ C H N O ] M , 8 1 0 4 2 = 0 . 0 5 0 [ C H N O H ] M , 8 1 0 4 2 + = 5 . 0 Γ— 1 0 βˆ’ 3 and [ O H ] M ? – = 2 . 5 Γ— 1 0 βˆ’ 3

  • A 2 . 5 Γ— 1 0 βˆ’ 2
  • B 1 . 3 Γ— 1 0 βˆ’ 5
  • C 1 . 3 Γ— 1 0 βˆ’ 4
  • D 2 . 5 Γ— 1 0 βˆ’ 4

Q20:

In a solution of acetic acid ( C H C O H ) 3 2 at equilibrium, [ H O ] M 3 + = 1 . 9 0 Γ— 1 0 βˆ’ 3 , [ C H C O ] M 3 2 – = 1 . 9 0 Γ— 1 0 βˆ’ 3 and [ C H C O H ] M 3 2 = 0 . 1 9 8 . What is the value of 𝐾 a for C H C O H 3 2 ?

  • A 1 . 0 4 Γ— 1 0 2
  • B 5 . 4 8 Γ— 1 0 4
  • C 9 . 6 0 Γ— 1 0 βˆ’ 3
  • D 1 . 8 2 Γ— 1 0 βˆ’ 5
  • E 7 . 1 5 Γ— 1 0 βˆ’ 7

Q21:

In an aqueous solution at equilibrium, [ O H ] M , [ N H ] M a n d [ N H ] M – 4 + 3 = 4 . 3 8 Γ— 1 0 = 4 . 3 8 Γ— 1 0 = 1 . 0 6 6 βˆ’ 3 βˆ’ 3 . Calculate the value of 𝐾 b for N H 3 .

  • A 5 . 5 6 Γ— 1 0 4
  • B 4 . 1 1 Γ— 1 0 βˆ’ 3
  • C 2 . 4 3 Γ— 1 0 2
  • D 1 . 8 0 Γ— 1 0 βˆ’ 5
  • E1.07

Q22:

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

  • AWhen the temperature is not 2 5 ∘ C .
  • BIn nonaqueous systems.
  • CWhen a strong acid or base is involved.
  • DWhen a weak acid or base is involved.
  • EOnly at very low concentrations.