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Lesson Worksheet: Degree of Dissociation Chemistry

In this worksheet, we will practice defining and calculating the degree of dissociation of a weak acid and using it to derive Ostwald’s law of dilution.

Q1:

Which of the following statements best describes the degree of dissociation of an acid?

  • AThe probability that the acid will dissociate in an aqueous solution
  • BThe fraction of reactant molecules that dissociate at equilibrium
  • CThe total number of hydrogen atoms that can dissociate from a molecule
  • DThe concentration of the acid at equilibrium
  • EThe fraction of ionic species produced at equilibrium

Q2:

A weak acid with a dissociation constant of 1.54×10 mol/L is found to be 1.26% dissociated. What is the concentration of [H]+ ions? Give your answer to 2 decimal places.

  • A1.94×10 mol/L
  • B8.45×10 mol/L
  • C9.70×10 mol/L
  • D1.22×10 mol/L
  • E1.88×10 mol/L

Q3:

A 0.3 M solution of benzoic acid was found to be 1.47% dissociated. What is the value of 𝐾, to 2 decimal places, for this acid? Assume 1𝛼1.

  • A6.48×10 mol/L
  • B4.41×10 mol/L
  • C4.26×10 mol/L
  • D1.32×10 mol/L
  • E4.9×10 mol/L

Q4:

To 1 decimal place, what is the degree of dissociation for a 0.25 M solution of phenol at 25C? The dissociation constant 𝐾 is 1.6×10 M.

  • A2.5×10
  • B1.4×10
  • C4.0×10
  • D4.0×10
  • E6.4×10

Q5:

The equations below show a form of Ostwald’s law of dilution along with its simplified form:

𝐾=𝛼(1𝛼),𝐾=𝛼.vv

Which of the following approximation results in the simplified form of the equation?

  • AWhen 𝛼 is very small, (1𝛼) can be approximated to be equal to 1.
  • BFor strong acids, 𝛼 approaches 1, and so (1𝛼) can be approximated to be equal to 0.
  • CWhen 𝛼 is very large, (1𝛼) can be approximated to be equal to 0.
  • DWhen v is very large, (1𝛼) can be ignored in the equation.

Q6:

Which of the following factors would increase the degree of dissociation of a weak acid?

  • AIncreasing dilution
  • BDecreasing volume
  • CDecreasing dilution
  • DIncreasing acid concentration

Q7:

According to Ostwald’s law of dilution, which of the following is the correct relationship between the dissociation constant (𝐾) and the degree of dissociation (𝛼)? Assume that 1𝛼1.

  • A𝐾=𝐶𝛼
  • B𝐾=𝛼𝐶
  • C𝐾=𝛼𝐶
  • D𝐾=𝛼𝐶
  • E𝐾=𝛼𝐶

Q8:

Formic acid (HCOOH) is a common weak acid that is found primarily in wood ants. If 0.02 mol of HCOOH is dissolved into 1 L of water at 25C, what is [HO]3+ if 𝐾 of HCOOH is 1.8×10? Give your answer to 1 decimal place.

  • A2.7×10 mol/L
  • B9.5×10 mol/L
  • C1.9×10 mol/L
  • D3.6×10 mol/L
  • E1.1×10 mol/L

Q9:

You are given 5 acidic solutions in a lab experiment, and each acid exhibits a different degree of dissociation, as seen in the table.

AcidHUHWHXHYHZ
Degree of Dissociation2.8%5.9%11.2%6.7%7.9%

Which acid has better electrical conductivity? Assume that their concentration is the same and that room temperature is maintained.

  • AHY
  • BHU
  • CHW
  • DHZ
  • EHX

Q10:

Which of the following is true about weak acids?

  • ATheir degree of ionisation is very high.
  • BTheir degree of ionisation is very small.
  • CThey are completely ionised in water.
  • DTheir degree of ionisation is moderate.

This lesson includes 17 additional questions and 25 additional question variations for subscribers.

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