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Hi, I'm Jessica
嗨，我是Jessica
and today I'm gonna talk about a reaction I like to call
今天我要讲的化学演示叫作
"Midas' magic"
"迈达斯的魔术"
and before I get started, let's watch the reaction in action
在开始之前，我们先来看看实际反应
with the help of Dr. Bassam Shakhashiri
演示由Bassam Shakhashiri博士来做
and here he is
这就是他了
he's actually the president of the American Chemical Society
他是美国化学学会主席
and his motto is science is fun
他的格言是，科学很有趣
Here he is at MIT and let's see what he has to show us
他来到MIT，看他是怎么做的
Watch this. I take this clear and colorless liquid
看这个，这是一种无色透明液体
and I put some of it into beaker, about 100 milliliters
将一些倒入烧杯，大约100毫升
How do I know it's about 100 milliliters?
我怎么知道大约是100毫升
I'm reading the markers here on the beaker
我阅读了烧杯上的刻度
and I take about 100 milliliters of a bit different clear and colorless liquid
再倒100毫升的另一种无色透明液体
but you don't know it's different, they look the same
但你们不知道它不同，因为看起来是一样的
and look at this look, look what's gonna happen now?
看这个，看看会发生什么
Isn't one of the most fascinating observations you make?
这非常迷人，不是吗
You take 2 clear colorless liquid, you mix them together
将两种无色透明液体混合
and you get a yellow substance that is insoluble in water
却得到了一种不溶于水的黄色物质
This is lead iodide
这是碘化铅
I mixed potassium iodide solution with lead nitrate solution
我混合了碘化钾溶液和硝酸铅溶液
So the magician never tells you how the trick works
魔术师不会告诉你们为什么会这样
but in science we like to know what's going on
但科学中，我们会解释发生了什么
So what is going on? Let's break it down
发生了什么呢，我来讲解一下
Dr. Shakhashiri started with two clear colorless liquids
Shakhashiri博士使用了两种无色透明液体
He had about 100 milliliters of lead nitrate
他用了大约100毫升的硝酸铅
and that aqueous, it's in solution
这是溶于溶液的
and about 100 milliliters of potassium iodide
还有大约100毫升的碘化钾
also aqueous
也是溶液状态
and when he mixed those together
将两者混合
he got a yellow precipitate
他得到了黄色沉淀
Let's color that in yellow
我用黄色来表示
A precipitate is a solid
沉淀物是一种固体
So how do we know what this yellow solid is?
我们怎么知道这种黄色固体是什么呢
Well, this is a reaction that's called a double displacement reaction
这种反应被叫作复分解反应
And in this kind of reaction
这种反应中
the cation and anion pairs switch places
阳离子和阴离子相互交换
So what exactly does that mean?
什么意思呢
I'm gonna use some colors to help me out
我将用些色彩来描述
So we've got cations and anions in each of these compounds
这两种化合物中都有阳离子和阴离子
The cations have positive charge, so
阳离子具有正电荷
in this case it's led which has a 2+ charge
这里铅离子具有2+电荷
and nitrate, N03-
然后是硝酸根离子 NO
You need 2 of those to have a neutral compound
这需要两个，才能得到中性化合物
Our other compound over here has potassium
这里另一种化合物拥有钾离子
which has a +1
电荷是+1
an our anion is iodide
而阴离子是碘离子
which is -1
电荷是-1
