Marcia Barbosa – TRANSCRIPT
I do love water. I love to swim, to surf, and even to drink water. And do you know why I love water? Because I am water! Two-thirds of our body is made of water. And because of that, for the last fifteen years, kind of since high school, I have been studying water. And I have a secret to tell you: water is weird, pretty weird. OK, it’s weird, but it’s also fundamental to our lives, and fortunately, 70% of the planet is covered with water. But unfortunately, just 1% is clean water, 1% is water that we might be able to drink.
And that’s too little. Today, one in six people has lack of fresh water. And in 2050, it will be one in two people with lack of fresh water. Either you or me will have lack of fresh water. So, the world needs fresh water.
Please, don’t panic, because today I’m going to tell you how we can use the weirdness of water to help us get more fresh water. So, you see, water is very important. But when I tell people I work with water, they usually say to me, “Well, such a simple molecule. We know everything about water.” Even my mom tells me this. But that’s not true. Water is not simple, and you have many things in water that we still need to understand. OK. You’re not convinced.
Let’s compare water with another material: with silicon. Silicon is also abundant on the planet. 28% of the crust of the Earth is composed of silicon. And silicon also has a number of unique properties. And the fact that silicon has unique properties and that we have learned how to use these unique properties of silicon allows us today to have cell phones, computers, flat screens and all these instruments that govern our lives today. And, you know what? Silicon has just half a dozen anomalies.
Water? Water has seventy. Yes, 70 anomalies. So, it’s our duty to find ways to use these anomalous behaviors of water to have more clean water. So, how are we going to do that? Before answering this question, let me introduce you to two of the seventy anomalies of water.
The first anomaly is the density anomaly. Most liquids contract under cooling. Water does the contrary. If you cool water, it expands. And that’s why ice, that you see on the screen, floats into liquid water, because ice occupies more volume, it is less dense, and it floats on the liquid surface. But much more interesting than ice floating into liquid water is the fact that zero-temperature water floats in four-temperature water.
See the beauty? When you have winter in the northern hemisphere, you have ice, followed by zero-temperature water, and far, at the bottom of the river or lake, you have the warm four-centigrade water, with fish and plants surviving. If water was as common as other materials, in the first winter, in the glacial time, it would freeze from the bottom to the top, and all life would be killed. It’s not that cool — literally cool.
So, now I come with the second anomaly. The second anomaly is the diffusion anomaly and it’s related to mobility. Water, when it’s denser, when it’s more compact, its molecules move faster. “OK, OK, Marcia is saying something wrong with that. I know that when I have more cars into traffic, the cars move slower. When I have more people in the shopping center, people move slower.” Water, when you have more water molecules, they move faster. Is not that bizarre? So, come one, what’s the mechanism for that? For that, I’m going to give you just a little class of physics.
So, water is composed of one oxygen, the big guy, and two hydrogens. And inside the water molecule, the interaction is the covalent interaction. But between molecules you have a second interaction, the hydrogen-bond interaction. So, what’s the difference between the two of them? Covalent is very close, is very strong and is very tight. Hydrogen bond is further apart and is twenty times weaker. OK? So, covalent bond is like marriage, or is like what marriage was supposed to be. You know, the particles are moving together and they’re very tight. Hydrogen bond is more like flirting. You are more distant, you flirt here, you flirt there, you flirt everywhere. OK.
Now I got it. I got it. When I decrease the temperature and I have ice, I have all the particles together, and all the hydrogen bonds made. So, I’m further apart like frozen, I don’t move, but I have the hydrogen bonds. I heat a little bit the system, I break the bonds and particles can actually approach, and that’s why ice floats into water. But how does this increase mobility? Easy. It’s easier to flirt in a crowded party than to flirt in an empty party.
So, that’s why molecules actually move around when they have more particles, making bonds, disrupting bonds, making bonds, disrupting bonds. Isn’t that cool? But, you know, not always hydrogen bonds are a good thing. This deep and great love water has for making bonds might make water end up in bad company. Water might make bonds with something that is poisonous to us, or something that makes water undrinkable, like salt. So, the bonds are not always a good thing and, actually, the industry uses this property of water making bonds to throw away the waste or to produce things.