كيف يحسب الرقم الهيدروجيني pH للمحاليل؟ How to calculate pH and pOH?

يحسب الرقم الهيدروجيني بالعلاقة: pH = -log[H⁺]، وللمحاليل المائية عند 25°C: pH + pOH = 14. إذا كان pH 7 فالمحلول قاعدي. [الصيغة الرمزية الموزونة: pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴]

D4.3Theme D — Continuity and change

Climate change — IB Biology SL Revision Notes & Topical Questions

10 min read 12 parts Lesson 12 of 14 2 quizzes

📚 IB Biology SL Hub / Topical Revision

Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution

pH = -log[H⁺]  |  pOH = -log[OH⁻]  |  pH + pOH = 14  |  [H⁺][OH⁻] = 10⁻¹⁴

Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14

Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.

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Lesson summary

D4.3 Climate change — IB BIOLOGY SL notes: Explain the causes of climate change, the feedback cycles that accelerate it, its effects on ecosystems and ways to increase carbon sequestration.Greenhouse effect = greenhouse gases absorb radiation re-emitted from the Earth's surface a…

Anthropogenic climate change
Damaged carbon sinks
Methane (CH4)
Warming source
Positive correlation
Negative correlation

Part 1 of 9Greenhouse effect

1Greenhouse effect

Greenhouse effect greenhouse gases absorb radiation re-emitted from the Earth's surface and trap it in the atmosphere

Radiation from the Sun warms the surface, which radiates it back as infrared.
It is natural and essential for life.
Without it Earth would swing in temperature like Mars, from about 20 °C to -153 °C.

2Greenhouse gases

Greenhouse gases carbon dioxide and methane, among others

3Anthropogenic climate change

Anthropogenic climate change atmospheric warming and climate change thought to be caused by human activities

Terms

The greenhouse effect is the natural effect of the atmosphere.
Global warming is the rise in global temperature, mainly from increased greenhouse gases.
Climate change is the long-term change in climate measures such as temperature, precipitation and wind patterns.

Part 2 of 9Methane

Methane (CH₄)

Methane (CH₄) a simple hydrocarbon and the main component of natural gas
Some bacteria produce it naturally, but levels have risen sharply in the last 150 years.

Human sources

The guts of farmed ruminant mammals such as cattle.
Decomposing organic waste in landfill.
Extraction of fossil fuels.
Anaerobic bacteria in waterlogged rice paddies.

Warming source

Warming source thawing permafrost releases methane from natural stores

Feature	Carbon dioxide	Methane	Water vapour
Main human sources	Fossil fuels and deforestation	Cattle, rice paddies, landfill and gas leaks	Indirect, as warmer air holds more
Warming per molecule	Lower	Much higher	Moderate
Time in atmosphere	Centuries	About a decade	Days
Removed by	Photosynthesis and ocean uptake	Oxidation to CO₂	Precipitation

Part 3 of 9Correlation and causation

Positive correlation

Positive correlation both variables rise together

Negative correlation

Negative correlation one variable rises as the other falls

Antarctic ice cores

Antarctic ice cores they show a positive correlation between global temperature and atmospheric CO₂ over hundreds of thousands of years

Limits of correlation

It does not show that one variable caused the other.
It does not show which variable drives which.
An unknown third variable might be involved.

Causal support

Causal support the infrared absorption mechanism of CO₂ is known and tested, and other evidence supports a causal link

Part 4 of 9Positive feedback cycles

Positive feedback = the output of a process moves the system further from equilibrium
- It is destabilising and can drive a system to a tipping point where it shifts to a new state.
- Global warming leads to more global warming.

Loop	Trigger	Result	Why it speeds warming
Ice loss	Melting sea ice and snow	Dark ocean or land exposed	Lower albedo and more heat absorbed
Permafrost thaw	Warmer soil	Decomposition resumes	CO₂ and methane released
Faster decomposition	Higher soil temperature	More microbial respiration	More CO₂ from soils
Drought and fire	Hotter, drier summers	Forests burn or die	Stored carbon released and less uptake

1Albedo

Albedo the proportion of light a surface reflects

Snow and ice have a high albedo and rock, soil and dark ocean have a low albedo.

2Decomposition

Decomposition enzyme reactions run faster when warm, so peat bogs and permafrost release CO₂
Permafrost is frozen ground whose organic matter cannot decompose at low temperatures.

3Methanogenic archaea

Methanogenic archaea they become active as permafrost melts and produce methane

Global temperatures rise.

Permafrost begins to thaw.

Stored organic matter becomes available to microbes.

Decomposition releases CO₂ and methane.

Greenhouse gas concentration increases.

Further warming thaws more permafrost.

Part 5 of 9Boreal forests

Boreal forest (taiga)

Boreal forest (taiga) low productivity but vast, so an important carbon sink across North America, Europe and Russia

Tipping point

Tipping point warming may switch it from a carbon sink to a carbon source

Warmer temperatures mean less snow and so less meltwater.

Drought reduces photosynthesis in the conifers.

The trees lose green pigment, which is forest browning, and then die.

Dead trees dry out and the fire risk rises.

Burning releases CO₂ and reduces photosynthetic uptake.

Legacy carbon
- old carbon in living trees, needle litter and soil is released by combustion
- The switch can be irreversible.

Part 6 of 9Polar habitats and ocean currents

Sea ice

Sea ice landfast ice attached to land now breaks off earlier
Emperor penguins breed on Antarctic sea ice, and early break-up leaves too little time to raise chicks.
Walrus mothers must nurse further from the water, so calves are unguarded longer while mothers hunt.
Polar bears depend on sea ice to hunt seals.

Ocean currents

Ocean currents driven by wind, temperature and salinity differences
Warm currents carry heat from the tropics, so the Gulf Stream makes Europe warmer than Canada at a similar latitude.
Cold currents carry cold water towards the tropics.
Upwelling brings cold nutrient-rich water to the surface when wind pushes surface water away, supporting fisheries.

Effects of change

Effects of change altered currents change regional climate and marine life
El Niño warms the central Pacific, which blocks upwelling off South America and cuts primary production.
It also causes droughts, floods and other extreme weather.
Warmer surface water reduces upwelling of nutrients.

Part 7 of 9Range shifts

Tolerance limits

Tolerance limits a species must migrate or face extinction if conditions change beyond its range of tolerance

Poleward shift

Poleward shift a range moves towards the poles
Many North American trees have contracted and spread northward, since the northern limit is set by cold.

Upslope shift

Upslope shift a range moves to a higher altitude
On Mt Karimui in Papua New Guinea, between 1965 and 2014 most birds moved upslope, by an average of more than 100 m.
A few species stayed or moved downslope.

Limits

Limits species at mountain tops run out of habitat, and some species shift faster than their food

Part 8 of 9Coral reefs and ocean acidification

Coral reefs

Coral reefs built from calcium carbonate secreted by polyps living with algae
About 25% of ocean fish species depend on reefs.
Death of polyps disrupts food webs, reduces niches and biodiversity, and can collapse the ecosystem.

Bleaching

Bleaching high water temperatures make polyps expel their algae, and prolonged heat kills the polyps

Acidification

Acidification dissolved CO₂ forms carbonic acid, which dissociates and raises the hydrogen ion concentration
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃^- ⇌ 2H⁺ + CO₃^2-.
H⁺ combines with carbonate ions, which lowers the carbonate available for skeletons.
The oceans stay slightly alkaline but their pH falls towards neutral.
It shares a cause with warming (CO₂) but is not caused by warming.

Atmospheric CO₂ rises from fossil fuel combustion.

More CO₂ dissolves in seawater.

It forms carbonic acid and releases hydrogen ions.

Hydrogen ions combine with carbonate ions and lower their concentration.

Corals cannot build calcium carbonate skeletons easily.

Reefs grow slowly or dissolve, harming reef biodiversity.

Part 9 of 9Carbon sequestration

Carbon sequestration

Carbon sequestration capturing and storing atmospheric carbon dioxide in natural carbon sinks

Artificial storage is still at the research stage.
Cutting emissions matters more than relying on sinks alone.

Reforestation and afforestation

Reforestation and afforestation reforestation plants trees in deforested areas and afforestation creates new forest
Mature trees store huge amounts of carbon in their biomass.
Costa Rica now plants about seven times more trees than it cuts, helped by government benefits to landowners.

Peat bog restoration

Peat bog restoration peat forms where plant matter cannot decompose fully in waterlogged, acidic, anaerobic conditions
Draining bogs and harvesting peat release carbon by decay organisms and combustion.
Filling drainage ditches and regulating harvesting lets the bog grow deeper and sequester carbon again.

Soil carbon

Soil carbon no-till farming and cover crops store organic matter

Debate

Fast-growing non-native plantations sequester the most carbon in the shortest time.
Rewilding with native species is slower but better for biodiversity.
Stored carbon can be lost to fire.

Key terms

Term	Meaning
Greenhouse gas	A gas that absorbs radiation re-emitted from the Earth's surface and traps heat in the atmosphere.
Albedo	The proportion of light reflected by a surface.
Positive feedback	A process whose output moves a system further from its equilibrium.
Permafrost	Ground that remains frozen all year round.
Ocean acidification	A fall in ocean pH as dissolved CO₂ raises the hydrogen ion concentration.
Carbon sequestration	Capturing and storing atmospheric carbon dioxide.
Poleward shift	A change in the range of a species towards the poles.
Upwelling	The rise of cold, nutrient-rich deep water to the surface.

Avoid these mistakes

Saying the greenhouse effect is harmful in itself — it is natural and essential, and the problem is the enhanced effect

Saying a correlation between CO₂ and temperature alone proves cause — the mechanism and other evidence also support it

Saying ocean acidification is caused by global warming — it is caused by dissolved CO₂

Saying positive feedback stabilises a system — it moves the system further from equilibrium

Last updated: 18 October 2026