Ocean Chemistry, Carbon & Acidification — Practice · Grade 12 Science

Chapter: Pollution, Carbon & Climate Evidence

What this practice covers

By the end of Ocean Chemistry, Carbon & Acidification you should be able to:

8 questions, numeric and written answer, each with a worked explanation.

Vocabulary used: acidification, alkalinity, dissolved inorganic carbon.

Problem 1

pH falls by 1. Find hydrogen-ion concentration factor.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

10 times

10¹=10.

Problem 2

Can pH8.0 water be acidified relative to pH8.2?
Answer and explanation

Yes; its pH has declined even though it remains basic.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 3

pH drops by .20. Find hydrogen-ion factor 10^.20.
Hints

List the given quantities, select a relationship, and check units before substituting.

Answer and explanation

1.585 times

10^.20≈1.585.

Problem 4

Why not equate acidification with warming?
Answer and explanation

They are distinct processes: acidification changes chemistry; warming changes temperature, though they can interact.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 5

A pH drop is 0.3 units. Estimate the hydrogen-ion activity factor. Show the reasoning, not just the conclusion.
Hints

Acidification names a shift, not necessarily crossing neutral pH.

Answer and explanation

10^0.3≈2.0, about a doubling.

Problem 6

How can additional dissolved CO₂ affect carbonate availability?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Carbonate-system equilibria shift, often lowering carbonate ion availability and affecting saturation, depending on conditions.

Problem 7

One pH change cannot determine every carbonate concentrationOne pH change cannot determine every carbonate concentrationQuestionEnoughinformation?ReasonH⁺ ratio from ΔpHApproximate yes10^(−ΔpH)Carbonate concentration from pHaloneNoNeeds coupledchemistry/boundary dataShell-building responseNoNeeds saturation andbiological contextA pH ratio is not automatically a carbonate-loss percentage.
Original inference-limit comparison; no empirical carbonate-loss percentage is supplied.
Interpret the supplied visual. What is wrong with saying a 0.1 pH fall proves 26% less carbonate?
Answer and explanation

The 26% calculation concerns[H⁺]; carbonate requires additional coupled-equilibrium information.

A known pH difference supports a hydrogen-ion ratio under the stated convention. It does not by itself determine carbonate concentration or a shell-dissolution rate. Alkalinity summarizes seawater’s acid-neutralizing charge account and helps constrain carbonate chemistry alongside dissolved inorganic carbon and conditions. Saturation state compares chemical conditions with mineral equilibrium. Keep these distinct quantities rather than converting a 26% hydrogen-ion increase directly into 26% carbonate loss or 26% biological harm.

The 26% calculation concerns[H⁺]; carbonate requires additional coupled-equilibrium information.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 8

A seawater sample changes frompH8.1 topH7.9. Estimate the[H⁺] ratio and explain whether that proves a 58% carbonate decrease.
Answer and explanation

[H⁺] increases by 10^0.2≈1.585, about 58.5%. It does not prove the same carbonate decrease; alkalinity, dissolved carbon and coupled-equilibrium conditions are also required.

[H⁺] increases by 10^0.2≈1.585, about 58.5%.

It does not prove the same carbonate decrease; alkalinity, dissolved carbon and coupled-equilibrium conditions are also required.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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