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Place 01 · The Great Barrier Reef · Chapter 2 of 7
Salt Water Is Not Water
Seawater is 96.5% water. The other 3.5% is why the planet works.
About 15 minutes · 1 video · 1 simulation · 1 quick activity
Start here
The recipe is the same everywhere on Earth
Everyone knows the ocean is salty. Almost nobody knows that the recipe is nearly identical everywhere, from the Arctic to the Great Barrier Reef. Same ingredients, same ratios. Only the strength changes. And one of those ingredients is the calcium a coral builds its skeleton from.
Watch this
See it move
SciShow — Why’d the Ocean Stop Getting Saltier? Rivers keep delivering salt, so why isn’t the sea getting saltier every year?
While you watch, look for
- Where the salt comes from in the first place
- What keeps the ocean from getting saltier forever
- Something you did not expect. Hold onto it.
The short version
Three things going on here
The molecule
A lopsided little magnet
Water is bent, not straight, so one end is slightly negative and the other slightly positive. That uneven charge is why water can pull salt apart and hold it.
The superpower
It swallows heat
Water soaks up enormous amounts of heat before its temperature budges. That makes the ocean the planet’s thermostat, and it is why coastal towns have milder winters.
The recipe
About 35 grams per liter
Sodium and chloride make up most of it, then sulfate, magnesium, calcium and potassium, in the same proportions worldwide. Calcium is on that list for a reason.
Photos: Vilnis Husko, Nothing Ahead, Marina Leonova / Pexels
Play with it
Pull a water molecule apart
This is a real chemistry simulator. Open the Real Molecules tab and find water, H₂O. Turn on the charge view and watch where the electrons like to sit.
Simulation: Molecule Polarity, PhET Interactive Simulations, University of Colorado Boulder (CC BY 4.0).
Two questions to answer while you are in there
- Which end of the water molecule is more negative, the oxygen end or the hydrogen end?
- Why would a lopsided molecule be good at pulling salt crystals apart?
Try it yourself
Check yourself
Try it
Sort the Salt
Click the seven major ingredients dissolved in seawater. Watch out for the ones that are only there in tiny traces.
Try it · interactive
Build a Liter of Seawater
Mix the seven main salts until you have real seawater, then check your recipe.
Open the Build a Liter of Seawater in its own window (opens in a new tab).
Words you will hear
Four terms, that is all
Polarity
Water’s uneven electrical charge
Salinity
How much salt is dissolved
Parts per thousand
The unit: grams of salt per kilogram of seawater
Heat capacity
How much heat it takes to warm something up
Check your understanding
Practice the whole chapter
Everything in this chapter, in eight quick questions. Retry as often as you like. Read the feedback on every answer, right or wrong, because that is where the learning is.
Practice
Practice: Salt Water Is Not Water
Eight questions covering the video, the three cards, the four terms and the interactive above.
If you want more
Go deeper
- Our World Ocean 7.5–7.7 — LibreTexts · the friendliest version of this · 15 minutes
- Webb 5.1 and 5.3 — Properties of Water, Salinity Patterns — LibreTexts · 10 minutes
- TED-Ed: How polarity makes water behave strangely — Video · 5 minutes · optional
Photo credits (Pexels): Charlotte Youlten, Maahid Photos, Vilnis Husko, Nothing Ahead, Marina Leonova.