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Environmental chemistry

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Sample exercises

Grades 8–12 · Environmental chemistry

Does clear appearance prove that water is safe to drink?

  1. Only if it has no bubbles.
  2. Yes, always.
  3. No.
Answer and explanation

No.

Hazards can be invisible; this exercise makes no drinking-water determination.

Grades 8–12 · Environmental chemistry

A model sample contains 6 mg solute in 3 L. Find its mass concentration.

Answer and explanation

2 mg/L

6/3 = 2 mg/L.

Grades 8–12 · Environmental chemistry

What does below detection limit mean?

  1. The water contains no molecules.
  2. The method did not quantify the substance above its stated threshold.
  3. The substance is proven absent everywhere.
Answer and explanation

The method did not quantify the substance above its stated threshold.

Detection capability is limited.

Grades 8–12 · Environmental chemistry

Why should a water report include the sampling date and location?

Answer and explanation

Concentrations can vary across places and times.

Context is required before generalizing.

Grades 8–12 · Environmental chemistry

A measured concentration decreases from 10 to 4 mg/L. What is the percentage decrease?

Answer and explanation

60 %

(10 − 4)/10 × 100 = 60%.

Grades 8–12 · Environmental chemistry

Which statement is appropriately cautious?

  1. All water everywhere has 2 mg/L.
  2. This sample measured 2 mg/L with the stated method.
  3. The method guarantees universal safety.
Answer and explanation

This sample measured 2 mg/L with the stated method.

The conclusion should match the evidence scope.

Study notes