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So let's start with the basics
我们从基础开始考虑
What is an acid and a base?
酸和碱是什么
One definition is that
一种定义是
acids are compounds that donate a hydrogen ion
酸是一种化合物，它能贡献一个氢离子
or H plus
或者说H+
to another compound
给另一种化合物
and the compound that accepts that hydrogen ion is a base
而接受这个氢离子的化合物就是碱了
So acids are hydrogen ion donors
酸是贡献氢离子的物质
and bases are hydrogen ion acceptors
而碱则是接受氢离子的物质
Here are some examples
我举一些例子
Sodium hydroxide is a base
氢氧化钠是碱
It's used to make soap
能用于制造肥皂
And acetic acid which looks like this
而醋酸是酸，它是这样的
it makes vinegar sour
它让醋具有酸味
Alright, let's look back at our cylinders here
好，我们再来回头看这些柱形容器
This first set of cylinders contains the indicator bromothymol blue
第一组柱形容器中装的指示剂是溴百里酚蓝
Let's take a look at the spectrum
我们来看看光谱
Alright, so let's take a look at bromothymol blue
好，我们来看看溴百里酚蓝
the indicator in the first set of cylinders
这是第一组柱形容器中的指示剂
As you can see here, there's a scale of numbers. This is the pH scale
这里可以看到一些数字刻度，这些是pH值刻度
The higher the number, the more basic the solution
pH值越高，表示溶液碱性越强
the lower the number, the more acidic
pH值越低，表示酸性越强
So our solution started off basic
我们的溶液最开始是碱性的
It was blue and had sodium hydroxide in it
它是蓝色的，其中有氢氧化钠
And this is what the chemical structure of the molecule looks like when it's blue
这是指示剂分子呈蓝色时的化学结构
The chemical bonds in the molecule are absorbing
分子中的化学键能够吸收
colors of the visible spectrum that are not blue
蓝色以外的可见光谱
so blue is reflected back to our eyes
所以蓝色反射回我们的眼睛
Now if a compound picks up a hydrogen ion
但如果该化合物结合一个氢离子
which it would if you add an acid to it
加入酸时它确实会这样
the molecule changes color
此时分子会变色
Now it absorbs blue and reflects yellow
它开始吸收蓝光，并反射黄光
Since the colors depend on the structure of the molecule
由于颜色依赖于分子结构
a chemist could reprogram the molecule to switch its color at
化学家可以重新构造分子
other pHs, other numbers on this scale
让颜色变化发生在其它pH值上
That's useful depending on the kind of reactions she may want to study
这对于所要研究的化学反应很有用
Now nature experiments with color all the time
自然界也在不断使用着颜色
Animals use color to avoid predators, attracts mates
动物使用颜色来避开捕食者，吸引配偶
scare off enemies, etc
吓退敌人，等等
Alright, so now let's take a look at
好，我们再来看看
what's happening in the second set of cylinders that started off pink
第二组最开始是粉色的柱形容器中发生了什么
The indicator in there is phenolphthalein
这里的指示剂是酚酞
The same thing is happening as with our bromothymol blue
情况和溴百里酚蓝很类似
but this time when the solution is basic, it's pink
但这次，溶液呈碱性时，它是粉色
and when it's acidic, it's colorless
呈酸性时，则是无色
But why does adding dry ice
那么为什么加入干冰
change the solution from basic to acidic?
会让溶液从碱性变为酸性呢
Well, dry ice is solid carbon dioxide
因为干冰是固态二氧化碳
When you add it to water, it bubbles
加到水中时，它会冒泡
and part of every bubble of carbon dioxide dissolves
每个泡泡中都会有二氧化碳溶解
when it does, it forms carbonic acid. Let's look at that equation
这时就会生成碳酸，我们来看看方程式
So there's more and more carbonic acid in the water
水中的碳酸越来越多
and this acid reacts with the sodium hydroxide until there's none left
这种酸会同氢氧化钠反应，一直将其耗尽为止
So the solution becomes acidic
于是溶液变成酸性
So we saw our bromothymol blue
所以我们看到溴百里酚蓝
turning from blue to yellow as a solution became more acidic
随着溶液酸性越来越强，从蓝变黄
And we saw our phenolphthalein
而酚酞
turn from pink to colorless as it became more acidic
随着溶液酸性越来越强，从粉色变为无色
Now let's watch again what happens in the final set of cylinders
下面再来看看最后一组柱形容器中的实验
Alright, so now, I ask you to focus your attention on this cylinder
好，现在我要求你们注意这个柱形容器
Actually, you can focus your attention on anything you want to
实际上，你们也可以关注别的
You can even not pay attention if you want to
甚至不关注任何东西都行
We live in a free country
我们生活在一个自由的国度
But if you want to follow the experiment with me
但如果你想跟随我的实验步伐
I want you to focus your attention on this one
我希望你能关注这个
and tell me, count them out how many different color changes you see
数一下我加入干冰后有多少种颜色变化
as I dropped the dry ice in there
数一下我加入干冰后有多少种颜色变化
I'm listening to you on the radio
我是在收音机前听你们讲
One, wow, I heard wow, what kind of account is that?
一，哇,我听到有人说哇，这数的是什么
Three so far
目前我听到三了
Three different color changes
三种不同颜色变化
but you know I'm listening to you on the radio
但我是在收音机前听你们讲
You want me to appreciate what you're seeing
你们要让我理解你们看到了什么
So what were the color changes that you saw?
你们具体看到了什么颜色变化
Why couldn't you say those?
告诉我具体的
You see how we have to help our brain make the right observations
你们应该知道如何帮助大脑作出正确观测
and make the right reporting
并正确报告
OK so, in the final set of cylinders
在最后一组柱形容器中
Dr. Shakhashiri has a mixture of indicators
Shakhashiri博士使用了指示剂的混合物
This created the color changes that occurred as the solution became more and more acidic
这样一来，随着溶液酸性变强，颜色会多次变化
There were three changes that we saw
这里我们看到了三次变化
It went from purple to blue
首先是从紫色变为蓝色
to green
再变为绿色
to yellow
再变为黄色
Alright, that's it for me today
好，今天就到这里
I will see you next time
我们下次再见
