Water - Liquid Awesome: Crash Course Biology #2

Summary

This script from Crash Course HQ dives into the remarkable properties of water, essential for life on Earth. It highlights water's unique ability to exist in solid, liquid, and gas forms, emphasizing the significance of hydrogen bonds that give water its high cohesion, surface tension, and polarity. The video also explores water's role as an exceptional solvent, its heat capacity, and how ice floats due to hydrogen bonding. The script celebrates the eccentric Henry Cavendish, who first determined water's composition, and concludes with a review of water's life-sustaining properties.

Takeaways

• 💧 Water is a unique substance that naturally occurs in solid, liquid, and gas forms and is essential for life on Earth.
• 🌌 The search for water, especially liquid water, in the universe is a key interest for scientists and astronomers as it may indicate the possibility of extraterrestrial life.
• 🚀 The discovery of gypsum on Mars by the rover Opportunity suggests the existence of liquid water billions of years ago, sparking excitement about the potential for past life on the planet.
• 🔬 Water's molecular structure, H2O, with its polar nature, results in hydrogen bonds that give water its unique properties.
• 🔗 Hydrogen bonds create a high cohesion in water, leading to high surface tension, which allows certain insects and a few vertebrates to 'walk on water'.
• 🌱 Water's adhesion to surfaces like glass, combined with its cohesion, results in capillary action, allowing water to defy gravity and rise in narrow spaces.
• 🧪 Water is an exceptional solvent due to its polarity, capable of dissolving more substances than any other liquid on Earth.
• 🛡 Hydrophobic substances, which are non-polar and lack charged poles, do not dissolve in water due to the strong cohesive forces of water molecules.
• 🏵 Henry Cavendish, an eccentric scientist, was the first to recognize hydrogen gas and determine the composition of water, despite his unconventional methods and reluctance to publish his work.
• ❄️ The solid form of water (ice) is less dense than its liquid form due to the crystalline structure formed by hydrogen bonds, which is crucial for aquatic ecosystems and climate regulation.
• 🌡 Water has a high heat capacity, meaning it can absorb and retain heat, playing a significant role in moderating Earth's climate and enabling sweating as a cooling mechanism for the human body.

Q & A

Why is water considered the only substance on Earth that naturally occurs in solid, liquid, and gas forms?

Water is unique because it can exist in all three states of matter under normal conditions on Earth, making it the only substance with this property.

What is the significance of finding liquid water on other planets, such as on Mars?

The discovery of liquid water on other planets is significant because it suggests the potential for life, as water is a key ingredient for life as we know it.

What is the chemical formula for water and what does its molecular structure indicate about its properties?

The chemical formula for water is H2O, indicating two hydrogen atoms bonded to one oxygen atom. Its V-shaped molecular structure and polarity result in hydrogen bonding, which gives water many of its unique properties.

What is the importance of hydrogen bonds in water molecules?

Hydrogen bonds are crucial because they cause water molecules to attract each other, leading to properties like high cohesion, surface tension, and the ability to form capillary action.

Why does water have a high cohesion and surface tension?

Water's high cohesion and surface tension are due to hydrogen bonding, which causes water molecules to stick together more strongly than in most other liquids.

How does water's cohesive force allow some insects and a few vertebrates to walk on its surface?

The high surface tension of water, a result of its cohesive forces, can support the weight of small insects and some vertebrates, allowing them to 'walk on water'.

What is the difference between cohesion and adhesion in the context of water?

Cohesion is the attraction between water molecules, while adhesion is the attraction between water molecules and other substances, such as glass, which can cause water to spread out rather than bead up.

Why is water considered an amazing solvent?

Water is an amazing solvent because it can dissolve more substances than any other liquid on Earth, due to its polarity which allows it to break hydrogen bonds and surround dissolved polar substances.

What is a hydrophobic substance and how does it interact with water?

A hydrophobic substance is one that repels water. These substances are non-polar and do not dissolve in water because they cannot overcome the cohesive forces of water, essentially being pushed out.

Who was Henry Cavendish and what is his contribution to the understanding of water?

Henry Cavendish was a scientist who first recognized hydrogen gas as a distinct substance and determined the composition of water, showing that water is not an element but a compound of hydrogen and oxygen.

Why does ice float on water and what are the implications of this for life on Earth?

Ice floats on water because the hydrogen bonds in the crystalline structure of ice space the molecules apart, making it less dense than liquid water. This is crucial for life on Earth as it prevents bodies of water from freezing solid, which would disrupt aquatic ecosystems and climate regulation.

What is water's high heat capacity and why is it important for the Earth's climate and temperature regulation?

Water's high heat capacity means it can absorb and retain a lot of heat without a significant increase in temperature. This property is important for the Earth's climate as it helps to regulate temperatures and prevents rapid and extreme changes, especially in coastal areas.

How does the process of sweating help in cooling the body?

Sweating cools the body by evaporating water from the skin. As the water evaporates, it takes heat energy with it, leaving the body cooler.

Outlines

00:00

💧 The Marvels of Water's Properties

The script introduces water as a unique substance that exists naturally in solid, liquid, and gas forms on Earth. It emphasizes the importance of water for life and the excitement it generates in scientific communities, especially when found on other planets. The narrator discusses the molecular structure of water (H2O), highlighting its polarity and the formation of hydrogen bonds, which contribute to water's high cohesion and surface tension. These properties are crucial for phenomena like capillary action and the ability of some insects to 'walk on water'. The script also touches on water's role as an 'amazing' solvent due to its polarity, which allows it to dissolve more substances than any other liquid.

05:04

🔬 Henry Cavendish and Water's Unusual Behavior

This paragraph delves into the historical contributions of Henry Cavendish, a reclusive yet brilliant scientist who first recognized hydrogen gas and determined the composition of water. Despite the common belief in the 1700s that water was an element, Cavendish's experiments showed that hydrogen and oxygen react to form water. His work laid the groundwork for understanding specific gravity and even led to the discovery of the Earth's density. The script also explains water's anomalous property of having its solid form (ice) less dense than its liquid form, a characteristic attributed to the hydrogen bonds that form a crystalline structure in ice, making it float. This property is vital for aquatic ecosystems and global climate regulation.

10:08

🌡 Water's High Heat Capacity and Evaporation

The final paragraph discusses water's high heat capacity, which allows it to absorb and retain heat effectively, contributing to the regulation of Earth's temperature and climate. Oceans act as massive heat sinks, maintaining a stable temperature in coastal regions. The script also describes an experiment illustrating water's slow heat absorption when boiling. Additionally, it explains the cooling effect of water through the process of evaporation, which is the principle behind sweating. When the body heats up, water molecules on the skin break their hydrogen bonds and evaporate, taking heat energy with them and resulting in a cooling sensation.

Keywords

💡Hydrogen Bonds

Hydrogen bonds are a type of dipole-dipole attraction that occurs between a hydrogen atom covalently bonded to a highly electronegative atom (like oxygen) and another electronegative atom. In the context of the video, hydrogen bonds are crucial because they give water its unique properties. The script mentions that these bonds cause water molecules to be attracted to each other, forming a V-shape due to the slight negative charge on the oxygen atom and slight positive charge on the hydrogen atoms.

💡Cohesion

Cohesion refers to the intermolecular forces that cause molecules of the same substance to stick together. The video emphasizes that water has the highest cohesion of any non-metallic liquid, which is why it forms droplets or beads on surfaces like wax paper. Cohesion is a direct result of the hydrogen bonding between water molecules, as illustrated when the script talks about water's high surface tension and the ability of certain insects to 'walk on water'.

💡Adhesion

Adhesion is the attraction between different substances, such as water molecules and the surface of glass. The script explains that water spreads out on glass due to the adhesive forces being stronger than the cohesive forces within the water molecules. This concept is used to describe capillary action, where water climbs up a straw due to the combined effects of adhesion to the straw and cohesion among water molecules.

💡Capillary Action

Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces, like gravity. In the video, this phenomenon is explained through the lens of water's cohesion and adhesion properties, where water climbs up a straw due to the adhesive forces to the straw's material and cohesive forces among the water molecules themselves.

💡Solvent

A solvent is a substance that has the ability to dissolve other substances. Water, as described in the script, is an 'amazing solvent' because more substances can dissolve in it than in any other liquid. This is due to its polarity, which allows it to break the cohesive forces of water and surround the dissolved substances, such as sugar or salt.

💡Hydrophilic

Hydrophilic substances are those that are 'water-loving' and can dissolve in water due to their polarity. The script uses sugar and salt as examples of hydrophilic substances, which are able to dissolve because their polarity is stronger than the cohesive forces of water, allowing them to break the hydrogen bonds and be surrounded by water molecules.

💡Hydrophobic

Hydrophobic substances are 'water-fearing' and are non-polar, meaning they do not dissolve in water. The script explains that these substances cannot overcome the cohesive forces of water and are thus pushed out, making them an example of substances that do not dissolve in water.

💡Henry Cavendish

Henry Cavendish was a scientist known for his experiments with hydrogen and his role in determining the composition of water. The script mentions him as an eccentric genius who first recognized hydrogen gas as a distinct substance and contributed to the understanding of water's composition, despite his reclusive nature and limited publication of his work.

💡Heat Capacity

Heat capacity is the amount of heat energy needed to raise the temperature of a substance by a certain amount. The video script highlights water's high heat capacity, meaning it can absorb a lot of heat without a significant increase in temperature. This property is important for regulating Earth's climate and is also why water can be used for cooling, such as in sweating.

💡Evaporation

Evaporation is the process by which a liquid turns into a vapor, typically occurring when the liquid is heated. In the context of the script, when the body sweats, the water evaporates from the skin, taking heat energy with it and thus cooling the body. This is a critical process for thermoregulation in humans and other animals.

💡Polarity

Polarity refers to the separation of electric charges within a molecule, leading to a molecule having a positive and a negative end. In the video, polarity is essential for understanding why water is a good solvent and why hydrogen bonds form. The V-shaped structure of the water molecule, with the slightly negative oxygen and the slightly positive hydrogens, is a direct result of polarity.

Highlights

Water is the only substance on Earth that naturally occurs in solid, liquid, and gas forms.

The importance of water for life is emphasized, with its presence being a key indicator for potential extraterrestrial life.

The discovery of gypsum on Mars by the Opportunity rover suggests the past presence of liquid water, hinting at possible ancient life.

Water's necessity for life is linked to its unique molecular structure, H2O, and the covalent bonds between hydrogen and oxygen.

The polarity of water molecules leads to hydrogen bonding, which is crucial for many of water's properties.

Water's high cohesion and surface tension allow certain insects and a lizard to 'walk on water'.

Adhesion and capillary action are explained through the interaction between water and other substances like glass.

Water's polarity makes it an excellent solvent, capable of dissolving more substances than any other liquid on Earth.

Hydrophobic substances, which do not dissolve in water, are explained by their inability to overcome water's cohesive forces.

Henry Cavendish's eccentricity and scientific achievements, including determining the composition of water, are highlighted.

Cavendish's experiments with hydrogen and oxygen gases laid the groundwork for understanding water's molecular composition.

The unique property of ice floating on water is attributed to the crystalline structure formed by hydrogen bonds.

The significance of ice floating in maintaining aquatic ecosystems and preventing catastrophic climate changes is discussed.

Water's high heat capacity is explained as its ability to absorb and retain heat, influencing Earth's climate and temperature regulation.

The demonstration of water's heat capacity through cooking examples illustrates the concept in a relatable way.

Evaporation of water and its cooling effect is related to the body's natural cooling mechanism through sweating.

A review of the key properties and significance of water is provided, encouraging further learning and understanding.

Transcripts

Hello there.

Here at Crash Course HQ we like to start out each day with a nice healthy dose of water

in all it's three forms.

It's the only substance on all of our planet earth that occurs naturally in solid, liquid,

and gas forms.

And to celebrate this magical bond between two hydrogen atoms and one oxygen atom

here, today, we are going to be celebrating the wonderful

life sustaining properties of water.

But we're going to do it slightly more clothed.

Much better.

When we left of here at the Biology Crash Course, we were talking about life

and the rather important fact that all life as we know it is dependent upon there being

water around.

Scientists and astronomers are always looking out into the universe trying to figure out

whether there is life elsewhere

because that is kind of the most important question that we have right now.

They're always getting really excited when they find water someplace

particularly liquid water.

And this is one reason why I am so many other people geeked out so hard last December when

Mars' seven-year-old rover, Opportunity, found a 20-inch long vein of gypsum that was almost

certainly deposited by long-term liquid water on the surface of mars.

And this was probably billions of years ago, and so it's going to be hard to tell

whether or not the water that was there resulted in some life.

But maybe we CAN figure that out and that would be REALLY exciting!

But why?! Wy do we think that water is necessary for life?

Why does water on other planets get us so freaking excited?

So let's start out by investigating some of the amazing properties of water.

In order to do that we're going to have to start out with THIS

The world's most popular molecule -- or at least the world's most memorized molecule.

We all know about it. Good old H2O.

Two hydrogens, one oxygen. The hydrogens each sharing an electron with oxygen in what we

call a covalent bond.

So as you can see, I've drawn my water molecule in a particular way

and this is actually the way that it appears.

It is V-shaped. Because this big old oxygen atom is a little bit more greedy for electrons

it has a slight negative charge whereas this area here with the hydrogen atoms has a slight

positive charge.

Thanks to this polarity, all water molecules are attracted to one another -- so much so

they actually stick together, and these are called hydrogen bonds. We talked about them

last time.

Essentially what happens is that the positive pole around those hydrogen atoms bonds to

the negative pole around the oxygen atoms of a DIFFERENT water molecule.

And so it's a weak bond.

But look, they're bonding!

Seriously though, I cannot overstate the importance of this hydrogen bond.

So when your teacher asks you, "What's important about water?"

Start out with the hydrogen bonds and you should put it in all caps and maybe some sparkles

around it.

One of the cool properties that results from these hydrogen bonds is a high cohesion for

water, which results in high surface tension. Cohesion is the attraction between two like

things, like attraction between one molecule of water and another molecule of water.

Water has the highest cohesion of any non-metallic liquid, and you can see this if you put some

water on some wax paper or some Teflon or something where the water beads up.

Some leaves of plants do it really well. It's quite cool.

Since water adheres weakly to the wax paper or to the plant, but strongly to itself, the

water molecules are holding those droplets together in a configuration that creates the

least amount of surface area.

It's this high surface tension that allows some bugs and I think one lizard and also

one Jesus to be able to walk on water.

The cohesive force of water does have its limits of course. There are other substances

that water quite likes to stick to. Take glass for example.

This is called adhesions and the water is spreading out instead of beading up because

the adhesive forces between the water and the glass are stronger than the cohesive forces

of the individual water molecules in the bead of water.

Adhesion is attraction between two different substances. In this case the water molecules

and the glass molecules.

These properties lead to one of my favorite things about water: the fact that it can defy

gravity.

That really cool thing that just happened is called capillary action, and explaining

it can be easily done with what we now know about cohesion and adhesion.

Thanks to adhesion, the water molecules are attracted to the molecules in the straw. But

as the water molecules adhere to the straw, other molecules are drawn in by cohesion,

following those fellow water molecules. Thank you, cohesion! The surface tension created

here causes the water to climb up the straw. And it will continue to climb until eventually

gravity pulling down on the weight of the water in the straw overpowers the surface tension.

The fact that water is a polar molecule also makes it really good at dissolving things,

which makes it a good solvent.

Scratch that. Water isn't a GOOD solvent, it's an AMAZING solvent!

There are more substances that can be dissolved in water than in any other liquid on Earth.

Yes, that includes the strongest acid that we have ever created. These substances that

dissolve in water -- sugar or salt being ones that we're familiar with -- are called

hydrophilic, and they are hydrophilic because they are polar, and their polarity is stronger

than the cohesive forces of the water.

When you get one of these polar substances in water, it's strong enough that it breaks

all the little cohesive forces, all those little hydrogen bonds, and instead of hydrogen

bonding to each other the water will hydrogen bond around these polar substances.

Table salt is ionic, and right now it's being separated into ions as the poles of

our water molecules interact with it.

But what happens when there is a molecule that cannot break the cohesive forces of water?

It can't penetrate, and come into it. [Seriously...?]

Basically, what happens when that substance can't overcome the strong cohesive forces

of water? Can't get inside of the water?

That's when we get what we call a hydrophobic substance, or something that is fearful of

water. These molecules lack charged poles, they are non-polar and are not dissolving

in water because essentially they're being pushed out of the water

by water's cohesive forces.

Water: we may call it the universal solvent, but that does not mean that it dissolves everything.

There've been a lot of eccentric scientists throughout history, but all this talk about

water got me thinking about perhaps the most eccentric of the eccentrics -- a man named

Henry Cavendish.

He communicated with his female servants only via notes and added a staircase to the back

of his house to avoid contact with his housekeeper. Some believe he may have suffered from a form

of autism, but just about everyone will admit that he was a scientific genius.

He's best remembered as the first person to recognize hydrogen gas as a distinct substance

and to determine the composition of water.

In the 1700s most people thought that water itself was an element, but Cavendish observed

that hydrogen -- which he called inflammable air, reacted with oxygen -- known then by

the awesome name "dephlogisticated aire" -- to form water.

Cavendish didn't totally understand what he discovered, in part because he didn't

believe in chemical compounds and explained his experiments with hydrogen in terms of

a fire-like element called "phlogiston."

Nevertheless, his experiments were groundbreaking, like his work in determining the specific

gravity -- basically the comparative density -- of hydrogen and other gases with reference

to common air. It's especially impressive when you consider the crude instruments he

was working with. This, for example, is what he made his hydrogen gas with.

He went on to not only establish an accurate composition of the atmosphere, but also discovered

the density of the earth. Not bad for a guy who was so painfully shy that the only existing

portrait of him was sketched without his knowledge.

But for all his decades of experiments, Cavendish only published about 20 papers. In the years

after his death, researchers figured out that Cavendish had actually pre-discovered Richter's

Law, Ohm's Law, Coulomb's Law, several other laws...

that's a lot of freaking laws!

And if he had gotten credit for them all we would have had to deal with

Cavendish's 8th Law and Cavendish's 4th Law.

So I, for one, am glad that he didn't actually get credit.

We're going to do some pretty amazing science right now. You guys are not going to believe

this.

Ok, you ready?

It floats!

Yeah, I know you're not surprised by this, but you should be, because everything else,

when it's solid, is much more dense than when it's liquid, just like gases are much less

dense than liquids are.

But that simple characteristic of water: that it's solid form floats, is one of the reasons

why life on this planet, as we know it, is possible.

Why is it that solid water is less dense than liquid water while everything else is the

exact opposite of that?

Well, you can thank your hydrogen bonds once again.

So at around 32 degrees Fahrenheit, or 0 degrees Celsius if you're a scientist or from a part

of the world where things make sense

water molecules start to solidify and the hydrogen bonds in those water molecules form

crystalline structures that space molecules apart more evenly, in turn making frozen water

less dense than the liquid form.

So in almost every circumstance, floating water ice is a really good thing. If ice were

denser than water it would freeze and then sink, and then freeze and then sink, and then

freeze and then sink.

So just trust me on this one, you don't want to live on a world where ice sinks. Not

only would it totally wreak havoc on aquatic ecosystems, which are basically how life formed

on the Earth in the first place, but also all the ice at the North Pole would sink and

all of the water everywhere else would rise and we wouldn't have any land.

That would be annoying.

There's one more amazing property of water that I'm forgetting...

Why is it so hot in here?

Ah!

Heat capacity!

Yes, water has a very high heat capacity,and probably that means nothing to you, but basically

it means that water is really good at holding on to heat.

Which is why we like to put hot water bottles in our bed and cuddle with them when we're

lonely.

But aside from artificially warming your bed it's also very important that it's hard to

heat up and cool down the oceans significantly.

They become giant heat sinks that regulate the temperature and the climate of our planet.

Which is why, for example, it is so much nicer in Los Angeles, where the ocean is constantly

keeping the temperatures the same, than it is in Nebraska.

On a smaller scale we can see water's high heat capacity really easily and visually by

putting a pot with no water in it on a stove and seeing how badly that goes.

But then you put a little water in it and it takes forever to boil.

Oh, and if you hadn't already noticed this, when water evaporates from your skin

it cools you down.

That's the principal behind sweating, which is an extremely effective though somewhat

embarrassing part of life.

But this is example of another incredibly cool thing about water.

When my body gets hot and it sweats, that heat excites some of the water molecules on

my skin to the point that they break those hydrogen bonds and they evaporate away.

And when they escape, they take that heat energy with them, leaving me cooler.

Lovely.

This wasn't exercise though. I don't know why I'm sweating so much. It could be the

spray bottle that I keep spraying myself with or maybe it's just because this is such a

high stress enterprise: trying to teach you people things.

I think I need some water, but while I'm drinking, there's a review for all of the things we

talked about today. If there are a couple things you're not quite sure about just go

back and watch them. It's not going to take a lot of your time. And you're going to be

smarter, I promise.

You're going to do SO well on that test you either don't or do have coming up.

Ok, bye.