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FE · 7% of the exam

Environmental Chemistry practice questions

10 free Environmental Chemistry questions for the FE Environmental Exam (FE) exam, each with the correct answer and an explanation for every option.

Start the questionsFree 10-question FE quiz

What this domain covers

The chemistry of natural and engineered systems: stoichiometry, equilibrium, acid-base behaviour, redox reactions and how organic contaminants move between phases.

Exam weight
7%
On a real exam
≈ 8 questions
In our bank
40 questions

Topics that come up most

  • Stoichiometry and concentration units
  • Acid-base equilibria, pH and alkalinity
  • The carbonate system and hardness
  • Oxidation-reduction reactions
  • Solubility, sorption and partition coefficients

How to study it

Practise converting between mg/L, mol/L, meq/L and mg/L as CaCO3. Hardness and alkalinity questions depend on getting those conversions right.

Sample Environmental Chemistry questions

Try each one before opening the answer. Original questions written to the official exam objectives.

  1. Question 1

    Water contains 24.3 mg/L of magnesium (Mg²⁺, equivalent weight 12.15). Expressed as CaCO₃, the magnesium hardness is:

    • A24.3 mg/L, the Mg concentration
    • B100 mg/L
    • C50 mg/L
    • D200 mg/L
    Show answer and explanation

    Answer: B) 100 mg/L

    • AIncorrect. Convert to CaCO₃ equivalents.
    • BCorrect. (24.3/12.15) × 50.
    • CIncorrect. That's one milliequivalent.
    • DIncorrect. That doubles the result.

  2. Question 2

    Water contains 40 mg/L of calcium (Ca²⁺, equivalent weight 20). Its calcium hardness as CaCO₃ (equivalent weight 50) is:

    • A2,000 mg/L as CaCO₃
    • B40 mg/L as CaCO₃
    • C16 mg/L as CaCO₃
    • D100 mg/L as CaCO₃
    Show answer and explanation

    Answer: D) 100 mg/L as CaCO₃

    • AIncorrect. Multiply by 50/20, not 50.
    • BIncorrect. Convert using equivalent weights.
    • CIncorrect. That's inverted.
    • DCorrect. 40 × 50/20.

  3. Question 3

    Hypochlorous acid (HOCl) has a pKa of about 7.5. At pH 7.5, the free chlorine is:

    • ANearly all OCl⁻
    • BNearly all HOCl
    • CAbout half HOCl and half OCl⁻
    • DAll chloramines
    Show answer and explanation

    Answer: C) About half HOCl and half OCl⁻

    • AIncorrect. That's at higher pH.
    • BIncorrect. That's at lower pH.
    • CCorrect. At pH = pKa, the two forms are equal.
    • DIncorrect. Chloramines need ammonia.

  4. Question 4

    Benzene, toluene, ethylbenzene and xylenes (BTEX) are common groundwater contaminants associated with:

    • AFertilizer runoff
    • BGasoline releases
    • CRoad salt
    • DSeptic systems only
    Show answer and explanation

    Answer: B) Gasoline releases

    • AIncorrect. That brings nitrate.
    • BCorrect. Leaking fuel tanks are a typical source.
    • CIncorrect. That brings chloride.
    • DIncorrect. BTEX comes from petroleum.

  5. Question 5

    Water contains 122 mg/L of bicarbonate (HCO₃⁻, equivalent weight 61). Expressed as CaCO₃ (equivalent weight 50), the alkalinity is:

    • A122 mg/L as CaCO₃
    • B100 mg/L as CaCO₃
    • C149 mg/L as CaCO₃
    • D61 mg/L as CaCO₃
    Show answer and explanation

    Answer: B) 100 mg/L as CaCO₃

    • AIncorrect. Convert using equivalent weights.
    • BCorrect. (122/61) × 50.
    • CIncorrect. That's inverted.
    • DIncorrect. Recheck the conversion.

  6. Question 6

    Chloramines form when free chlorine reacts with:

    • AAmmonia
    • BOxygen
    • CSodium chloride
    • DCarbon dioxide
    Show answer and explanation

    Answer: A) Ammonia

    • ACorrect. They give a longer-lasting residual.
    • BIncorrect. That doesn't form chloramines.
    • CIncorrect. That's salt.
    • DIncorrect. That doesn't form chloramines.

  7. Question 7

    At 25 °C, a solution with pH 10 has a hydroxide concentration of:

    • A1 × 10⁻¹⁰ M
    • B1 × 10⁻⁴ M
    • C10 M
    • D1 × 10⁻⁷ M
    Show answer and explanation

    Answer: B) 1 × 10⁻⁴ M

    • AIncorrect. That's [H⁺].
    • BCorrect. pOH = 14 − 10 = 4, so [OH⁻] = 10⁻⁴ M.
    • CIncorrect. Use pOH = 14 − pH.
    • DIncorrect. That's neutral water.

  8. Question 8

    Aerating groundwater that contains dissolved Fe²⁺ removes iron because the iron is:

    • AReduced to metallic Fe⁰, which settles as dense particles
    • BOxidized to Fe³⁺, which precipitates as ferric hydroxide
    • COxidized to Fe³⁺, which stays dissolved as a colorless ion
    • DKept as Fe²⁺ and carried off attached to rising air bubbles
    Show answer and explanation

    Answer: B) Oxidized to Fe³⁺, which precipitates as ferric hydroxide

    Aeration supplies oxygen that oxidizes soluble Fe²⁺ to Fe³⁺. The Fe³⁺ precipitates as insoluble ferric hydroxide, which is removed by settling and filtration.

    • AIncorrect. Oxygen is an oxidant, so aeration oxidizes iron rather than reducing it. Metallic iron does not form.
    • BCorrect. Dissolved oxygen oxidizes soluble Fe²⁺ to Fe³⁺. At normal pH, Fe³⁺ is highly insoluble and forms Fe(OH)₃ floc, which is removed by settling and filtration.
    • CIncorrect. The oxidation step is right, but Fe³⁺ is far less soluble than Fe²⁺ at neutral pH. It precipitates as reddish-brown hydroxide instead of staying in solution.
    • DIncorrect. Aeration does not remove iron by flotation or stripping. Dissolved Fe²⁺ is not volatile and must be oxidized and precipitated before it can be filtered out.

  9. Question 9

    At 25 °C, a solution with pH 4 has a pOH of:

    • A7
    • B4
    • C18
    • D10
    Show answer and explanation

    Answer: D) 10

    • AIncorrect. That's neutral.
    • BIncorrect. Subtract from 14.
    • CIncorrect. Subtract, don't add.
    • DCorrect. pH + pOH = 14.

  10. Question 10

    Total hardness of water is mainly the sum of:

    • ACalcium and magnesium hardness
    • BSodium and potassium
    • CChloride and sulfate
    • DIron and turbidity
    Show answer and explanation

    Answer: A) Calcium and magnesium hardness

    • ACorrect. Usually expressed as mg/L CaCO₃.
    • BIncorrect. Those don't cause hardness.
    • CIncorrect. Those are anions.
    • DIncorrect. It's mainly Ca and Mg.

Environmental Chemistry: FAQs

How much of the FE exam is Environmental Chemistry?

Environmental Chemistry is 7% of the FE exam by the official exam guide's weighting, which on a 110-question form works out to roughly 8 questions. The real exam's exact split varies by form.

What does the Environmental Chemistry domain cover?

The chemistry of natural and engineered systems: stoichiometry, equilibrium, acid-base behaviour, redox reactions and how organic contaminants move between phases.

How should I study Environmental Chemistry for FE?

Practise converting between mg/L, mol/L, meq/L and mg/L as CaCO3. Hardness and alkalinity questions depend on getting those conversions right.

Where can I practise more Environmental Chemistry questions?

This page has 10 free Environmental Chemistry questions with answers. The ExamWize FE question bank has 40 questions in this domain. Every practice exam result breaks your score down by domain, and Review Mode re-drills the questions you missed.

Other FE topics

Also: 15 free questions across all topics, the FE cheat sheet and the study guide.

Get Environmental Chemistry exam-ready

The full FE bank has 40 Environmental Chemistry questions. Timed practice exams match the real exam's length and domain weights, every result shows your score per domain, and Review Mode re-drills the questions you missed.

See the full FE practice examsTake the free diagnostic

Not affiliated with NCEES; questions are original, written from the official exam outline, and never copied from the real exam.