美國科學基金會(NSF)、美國科學教師協會(NSTA)及美國國家廣播公司(NBC)合作，為化學年製作了一系列教學單元，名為「今日化學(Chemistry Now)」，每周推出一單元，預計製作31單元。內容涵蓋日常生活中的化學，包含了21世界的先進化學。以下是第三單元：「鏡」分子--香芹酮("Mirror" Molecule: Carvone)。
旁白：
"Mirror" Molecule: Carvone
Spearmint. Caraway. Dill.
A chewing gum flavor. A seed in rye bread. And an herb in pickles. Wouldnt seem they have anything in common, but they do. Reduce spearmint, caraway seed and dill to their essential oils and a sizable percentage of all three turn out to be made up of the same molecule: carvone.
How can you explain one molecule being responsible for distinctly different smells and tastes? With two hands, a mirror, a lightbulb and a pair of gloves.
Start with the basics: Carvones chemical formula tells you what its made of: 10 atoms of Carbon, 14 atoms of Hydrogen, and 1 atom of Oxygen. Just as important as how many atoms of what elements make up a molecule is how those atoms are bonded together and in what configuration, or structure.
We think of molecules, when and if we think of molecules, as having only one set structure. This is H2O, for example not this, or this. But a molecule like Carvone can have slightly different arrangements of their atoms and still be the same molecule like a girl who has different looks depending on how she parts her hair, or the way she wears a sweater. As long as how she rearranges her hair and clothes doesnt add or take away anything, shes still the same girl in the same outfit.
The carvone molecule has two slightly different looks or, as theyre called, stereoisomers: this one and this one. Stereoisomers are three-dimensional, but its easier to understand these two by looking at a standard two-dimensional drawing of their structures. Notice anything? The two are mirror images of each other. Some structures, like, say, a lightbulb, are the same in mirror image or side by side. But carvone stereoisomers are like a pair of hands: A hand and its mirror reflection will exactly match but hands arent the same side by side, or superimposed.
Actually, carvone stereoisomers are like left and right hands even down to their names: This one is R-carvone the R stands for the Latin word meaning right. The structure of this gives spearmint its taste and smell. Its mirror opposite is S-carvone the S stands for the Latin word meaning left. The way this one is arranged is what gives caraway its flavor and aroma and dill, too. In pure form, the two flavors are almost the same.
This kind of left-handed/right-handed molecule is called chiral. Carvone has chirality, terms, not coincidentally, from a Greek word meaning hand. The Greek word for nose is rhinous, yes, as in rhinocerous. which is the way well segue into this next part on how your nose and tongue work to distinguish the difference between the smells and tastes of spearmint or caraway or dill through specialized receptors that interact with molecules in very specific ways.
Think of some receptors as structured like baseball mitts specifically designed to pick up molecules with structures like baseballs but not footballs which have their own receivers. These receptors are so highly specialized that they interact distinctively with molecules that differ only in very small ways, like their handedness, almost as if some receptors are like right-handed gloves able to pick up only the R-carvone molecules, recognize them, and send a message to the brain saying Its spearmint!
And as if S-carvones only fit into left-handed glove receptors, who recognize them and tell the brain: Its caraway! or Its dill!
There you go: a handy explanation of carvone.
學習單
國中：Molecules, Isomers, and Our World
高中：Introduction to Enantiomers and Handedness
《上一單元：吉士堡化學--乳酪 ‖ 下一單元：化學鍵》
進一步參考資料
1. NBC Learn- Chemistry now
2. NSTA Blog
科學教師專業成長 Professional Development for Science Teachers
2011/04/23
今日化學 ：吉士堡化學—乳酪
Chemistry Now : Cheeseburger Chemistry—Cheese
美國科學基金會(NSF)、美國科學教師協會(NSTA)及美國國家廣播公司(NBC)合作，為化學年製作了一系列教學單元，名為「今日化學(Chemistry Now)」，每周推出一單元，預計製作31單元。內容涵蓋日常生活中的化學，包含了21世界的先進化學。以下是第二單元：吉士堡化學--乳酪(Chemistry of Cheeseburger--Cheeses)。
旁白：
The Chemistry of Cheese
AL ROKER, reporting:
You cant have a cheeseburger without it: cheese. Cheddar, Swiss, Mozzarella, Blue, Monterrey jack, Pepperjack. To keep the chemistry more basic, we wont deal here with whats called American or processed cheese.
Cheese is an ancient food, dating back some 4,000 years to when humans first domesticated goats, sheep, yaks and other mammals for meat and milk: the sole basic ingredient in cheese, then and today.
JULIE YU, The Exploratorium: Cheese is a very concentrated form of milk with the water removed.
ROKER: Turning milk into cheese involves a change in a substance from one common state of matter to another, in this case, from liquid to solid. Some of these changes can be physical those are changes that are reversible, like freezing water into a solid ice cube: it can melt into water again.
When a change involves a chemical reaction, it generally cant be reversed and turning liquid milk to solid cheese is a good example: the cheese can never go back to being milk again. Heres why:
YU: Were going to make the worlds simplest cheese.
ROKER: Julie Yu, a scientist at The Exploratorium in San Francisco whos funded by The National Science Foundation, starts with milk.
YU: Milk is composed of proteins, fats, sugars and water. The process of making cheese is somehow removing that water so that youre left with the concentrated mass of the proteins and fats.
ROKER: Thats not so easy. Milk is an emulsion: uncounted illions of globular protein molecules and droplets of fat are suspended in the liquid. How to separate those from the water, and concentrate them? Think of panning for gold. If the gold was in the form of tiny individual flecks, itd be impossible to pan out; itd just flow through any strainer with the water. The gold has to be in clumps, nuggets, to be sifted out. So how do you get the fats and proteins in liquid milk to form little nuggets so they can be separated from the water?
YU: Cheesemaking relies on changing the structure of the proteins that are in milk because in order to separate out the proteins from the water in our milk, we need to change their form.
ROKER: Its called denaturing, which is pretty much what it sounds like: changing the natural structure or qualities of something.
YU: Proteins are typically folded up in a three-dimensional structure. When theyre denatured, they relax into a long chain. And so those chains can tangle together and become enmeshed and they solidify in a way that you are able to strain them from the milk. In general, there are three ways to denature proteins: one is to introduce heat, one is to introduce high salt, and one is to introduce acid.
ROKER: Like the citric acid in lemon juice.
YU: Were going to use lemon juice today. The proteins are normally in tight little balls. The acid is going to relax them. And theyre going to coagulate, theyre going to stick together in this nice gooey mess. And were going to strain that out and that will give us the cheese.
Im going to pour this through a strainer that I have lined with some cheesecloth. And thats going to keep the solids behind, which we now call the curds. And the liquid, which we would call the whey, is going into this bowl.
ROKER: Yes, curds and whey, what Little Miss Muffet was eating, as she sat on whatever a tuffet is, before unexpected arachnid proximity prompted flight.
YU: Once we strain out all of the whey it firms up into this nice ball of fresh cheese. There are some fresh cheeses that are made this way, just by simply adding acid. But the majority of cheeses are made in another way. They use a bacteria and an enzyme in order to coagulate their proteins.
ROKER: An enzyme called rennet, which cheesemakers can buy in tablet form.
YU: Rennet is an enzyme thats actually in the stomach lining of most animals. Its made to digest milk proteins. Rennet further breaks down the proteins and creates this nice gooey mesh and gives you cheeses of different textures.
ROKER: Rennet may explain how those ancient ancestors of ours made the first cheese.
YU: Its possible that someone had a pouch made out of animal stomach and was holding milk inside of that. Any enzymes present in the stomach would break down the milk and when they poured out their milk they would have been surprised to find curds and whey.
ROKER: Today cheeses come in a global array - at least 670 different kinds are listed in a leading cheese database. Chemistry is the reason all those different textures and flavors develop during cheese processing and aging: fermentation, oxidation, dehydration, bacterial and mold growth. Theyre all chemical reactions. So, there you are: a basic explanation of the chemical processes that turn liquid milk into solid cheese and turn a hamburger into a cheeseburger.
學習單
國中：Blowing up balloons with yeast
高中：Kitchen Mystery
《上一單元：水的化學 ‖ 下一單元：分子結構》
進一步參考資料
1. NBC Learn- Chemistry now
2. NSTA Blog
旁白：
The Chemistry of Cheese
AL ROKER, reporting:
You cant have a cheeseburger without it: cheese. Cheddar, Swiss, Mozzarella, Blue, Monterrey jack, Pepperjack. To keep the chemistry more basic, we wont deal here with whats called American or processed cheese.
Cheese is an ancient food, dating back some 4,000 years to when humans first domesticated goats, sheep, yaks and other mammals for meat and milk: the sole basic ingredient in cheese, then and today.
JULIE YU, The Exploratorium: Cheese is a very concentrated form of milk with the water removed.
ROKER: Turning milk into cheese involves a change in a substance from one common state of matter to another, in this case, from liquid to solid. Some of these changes can be physical those are changes that are reversible, like freezing water into a solid ice cube: it can melt into water again.
When a change involves a chemical reaction, it generally cant be reversed and turning liquid milk to solid cheese is a good example: the cheese can never go back to being milk again. Heres why:
YU: Were going to make the worlds simplest cheese.
ROKER: Julie Yu, a scientist at The Exploratorium in San Francisco whos funded by The National Science Foundation, starts with milk.
YU: Milk is composed of proteins, fats, sugars and water. The process of making cheese is somehow removing that water so that youre left with the concentrated mass of the proteins and fats.
ROKER: Thats not so easy. Milk is an emulsion: uncounted illions of globular protein molecules and droplets of fat are suspended in the liquid. How to separate those from the water, and concentrate them? Think of panning for gold. If the gold was in the form of tiny individual flecks, itd be impossible to pan out; itd just flow through any strainer with the water. The gold has to be in clumps, nuggets, to be sifted out. So how do you get the fats and proteins in liquid milk to form little nuggets so they can be separated from the water?
YU: Cheesemaking relies on changing the structure of the proteins that are in milk because in order to separate out the proteins from the water in our milk, we need to change their form.
ROKER: Its called denaturing, which is pretty much what it sounds like: changing the natural structure or qualities of something.
YU: Proteins are typically folded up in a three-dimensional structure. When theyre denatured, they relax into a long chain. And so those chains can tangle together and become enmeshed and they solidify in a way that you are able to strain them from the milk. In general, there are three ways to denature proteins: one is to introduce heat, one is to introduce high salt, and one is to introduce acid.
ROKER: Like the citric acid in lemon juice.
YU: Were going to use lemon juice today. The proteins are normally in tight little balls. The acid is going to relax them. And theyre going to coagulate, theyre going to stick together in this nice gooey mess. And were going to strain that out and that will give us the cheese.
Im going to pour this through a strainer that I have lined with some cheesecloth. And thats going to keep the solids behind, which we now call the curds. And the liquid, which we would call the whey, is going into this bowl.
ROKER: Yes, curds and whey, what Little Miss Muffet was eating, as she sat on whatever a tuffet is, before unexpected arachnid proximity prompted flight.
YU: Once we strain out all of the whey it firms up into this nice ball of fresh cheese. There are some fresh cheeses that are made this way, just by simply adding acid. But the majority of cheeses are made in another way. They use a bacteria and an enzyme in order to coagulate their proteins.
ROKER: An enzyme called rennet, which cheesemakers can buy in tablet form.
YU: Rennet is an enzyme thats actually in the stomach lining of most animals. Its made to digest milk proteins. Rennet further breaks down the proteins and creates this nice gooey mesh and gives you cheeses of different textures.
ROKER: Rennet may explain how those ancient ancestors of ours made the first cheese.
YU: Its possible that someone had a pouch made out of animal stomach and was holding milk inside of that. Any enzymes present in the stomach would break down the milk and when they poured out their milk they would have been surprised to find curds and whey.
ROKER: Today cheeses come in a global array - at least 670 different kinds are listed in a leading cheese database. Chemistry is the reason all those different textures and flavors develop during cheese processing and aging: fermentation, oxidation, dehydration, bacterial and mold growth. Theyre all chemical reactions. So, there you are: a basic explanation of the chemical processes that turn liquid milk into solid cheese and turn a hamburger into a cheeseburger.
學習單
國中：Blowing up balloons with yeast
高中：Kitchen Mystery
《上一單元：水的化學 ‖ 下一單元：分子結構》
進一步參考資料
1. NBC Learn- Chemistry now
2. NSTA Blog
今日化學 ：水的化學
Chemistry Now : Chemistry of Water
美國科學基金會(NSF)、美國科學教師協會(NSTA)及美國國家廣播公司(NBC)合作，為化學年製作了一系列教學單元，名為「今日化學(Chemistry Now)」，每周推出一單元，預計製作31單元。內容涵蓋日常生活中的化學，包含了21世界的先進化學。以下是第一單元：水的化學(Chemistry of Water)。
旁白：
Chemistry Now: Molecule Profile: H20 - Water
It might just be the most universally known fact in chemistry: the chemical formula for water - H2O.
A model of H2O doesnt look like much two small atoms of Hydrogen, the H2 part of H2O, attached to one bigger atom of Oxygen, the O part of H2O. Kind of like a cartoon drawing of a teddy bear and actually, water is kind of funny.
Fun Facts: Water H2O is the only natural substance on Earth found in all three common states of matter: liquid, solid, and gas, or vapor.
Its also one of the only common substances that is less dense in solid form than in liquid form. And water can dissolve more substances than any other liquid.
Lets focus on H2O in liquid form: What gives water its remarkable qualities and abilities?
Its all in the molecules content and structure not just what each H2O molecule is made of, but how the atoms are positioned, in what configuration and shape, and how they are bound together.
In water, just so youll know for later, the Hs and O are held together by covalent bonds by sharing electrons.
H2O is a polar molecule: The same way our planet has North and South Poles on opposite sides, the H2O molecule has two poles on opposite sides. And like a magnet, H2O has one positive end and one negative end.
Thinking of that cartoon teddy bear again, the chin side of the Oxygen atom has a slight negative electrical charge; the opposite side the side with the two Hydrogen ears has a slight positive electrical charge.
This might just be the second most universally known bit of chemistry: opposites attract. The positive Hydrogen side of every H2O molecule is going to attract, and be attracted to, the negative Oxygen sides of other nearby H2O molecules, in all directions. More and more of them pull closer and closer together until theyre like people in a hot, crowded dance club, packed so close together they can hardly move, but still turning and moving wildly.
Molecules that stay close to each other are called cohesive and water is highly cohesive. A pentillion even hextillion of chaotically-moving, tightly-packed H2O molecules cohere to make a single raindrop.
As good as water molecules are at all this cohering and convening, they also form bonds with surfaces and molecules unlike themselves a force called adhesion, as in adhesive. Pour the water out of a glass, and the inside of the glass is still wet: some H2O molecules stick or adhere to the silica molecules in the glass.
Being cohesive and adhesive is what makes water a (near) universal solvent. How? Take salt, or sodium chloride sodium ions, abbreviated as Na-plus, and chloride ions, abbreviated as Cl-minus, in a crystal.
As soon as a salt crystal hits the water, its rushed by a molecular mob of H2O molecules that break it apart; separate the sodium and chloride ions kind of a chemical divide and conquer.
Because sodium ions have a positive charge, each one is swarmed by H2O molecules flying at it with their negatively-charged Oxygen sides, completely surrounding the sodium ion, isolating it, carrying it off in a turbulent sea of H2O molecules.
The same thing happens in reverse to the chloride ions, which have a negative charge each of those is surrounded and isolated by H2O molecules leading with their positively-charged hydrogen sides.
Each salt crystal is broken into tiny pieces dissolved by, and into, the water.
Theres much, much more to know about H2O and how it works to keep every living thing on the planet and maybe other planets alive.
Think of this video as a drop in the bucket.
學習單
國中：Density Comparison of Water and Ice
高中：Water is a Polar Molecule
‖ 下一單元：吉士堡化學--乳酪》
進一步參考資料：
1. NBC Learn- Chemistry now
2. NSTA Blog
旁白：
Chemistry Now: Molecule Profile: H20 - Water
It might just be the most universally known fact in chemistry: the chemical formula for water - H2O.
A model of H2O doesnt look like much two small atoms of Hydrogen, the H2 part of H2O, attached to one bigger atom of Oxygen, the O part of H2O. Kind of like a cartoon drawing of a teddy bear and actually, water is kind of funny.
Fun Facts: Water H2O is the only natural substance on Earth found in all three common states of matter: liquid, solid, and gas, or vapor.
Its also one of the only common substances that is less dense in solid form than in liquid form. And water can dissolve more substances than any other liquid.
Lets focus on H2O in liquid form: What gives water its remarkable qualities and abilities?
Its all in the molecules content and structure not just what each H2O molecule is made of, but how the atoms are positioned, in what configuration and shape, and how they are bound together.
In water, just so youll know for later, the Hs and O are held together by covalent bonds by sharing electrons.
H2O is a polar molecule: The same way our planet has North and South Poles on opposite sides, the H2O molecule has two poles on opposite sides. And like a magnet, H2O has one positive end and one negative end.
Thinking of that cartoon teddy bear again, the chin side of the Oxygen atom has a slight negative electrical charge; the opposite side the side with the two Hydrogen ears has a slight positive electrical charge.
This might just be the second most universally known bit of chemistry: opposites attract. The positive Hydrogen side of every H2O molecule is going to attract, and be attracted to, the negative Oxygen sides of other nearby H2O molecules, in all directions. More and more of them pull closer and closer together until theyre like people in a hot, crowded dance club, packed so close together they can hardly move, but still turning and moving wildly.
Molecules that stay close to each other are called cohesive and water is highly cohesive. A pentillion even hextillion of chaotically-moving, tightly-packed H2O molecules cohere to make a single raindrop.
As good as water molecules are at all this cohering and convening, they also form bonds with surfaces and molecules unlike themselves a force called adhesion, as in adhesive. Pour the water out of a glass, and the inside of the glass is still wet: some H2O molecules stick or adhere to the silica molecules in the glass.
Being cohesive and adhesive is what makes water a (near) universal solvent. How? Take salt, or sodium chloride sodium ions, abbreviated as Na-plus, and chloride ions, abbreviated as Cl-minus, in a crystal.
As soon as a salt crystal hits the water, its rushed by a molecular mob of H2O molecules that break it apart; separate the sodium and chloride ions kind of a chemical divide and conquer.
Because sodium ions have a positive charge, each one is swarmed by H2O molecules flying at it with their negatively-charged Oxygen sides, completely surrounding the sodium ion, isolating it, carrying it off in a turbulent sea of H2O molecules.
The same thing happens in reverse to the chloride ions, which have a negative charge each of those is surrounded and isolated by H2O molecules leading with their positively-charged hydrogen sides.
Each salt crystal is broken into tiny pieces dissolved by, and into, the water.
Theres much, much more to know about H2O and how it works to keep every living thing on the planet and maybe other planets alive.
Think of this video as a drop in the bucket.
學習單
國中：Density Comparison of Water and Ice
高中：Water is a Polar Molecule
‖ 下一單元：吉士堡化學--乳酪》
進一步參考資料：
1. NBC Learn- Chemistry now
2. NSTA Blog
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