評論
打印
So let's start with the basics
我們從基礎(chǔ)開始考慮
What is an acid and a base?
酸和堿是什么
One definition is that
一種定義是
acids are compounds that donate a hydrogen ion
酸是一種化合物，它能貢獻(xiàn)一個(gè)氫離子
or H plus
或者說H+
to another compound
給另一種化合物
and the compound that accepts that hydrogen ion is a base
而接受這個(gè)氫離子的化合物就是堿了
So acids are hydrogen ion donors
酸是貢獻(xiàn)氫離子的物質(zhì)
and bases are hydrogen ion acceptors
而堿則是接受氫離子的物質(zhì)
Here are some examples
我舉一些例子
Sodium hydroxide is a base
氫氧化鈉是堿
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，它是這樣的
it makes vinegar sour
它讓醋具有酸味
Alright, let's look back at our cylinders here
好，我們再來回頭看這些柱形容器
This first set of cylinders contains the indicator bromothymol blue
第一組柱形容器中裝的指示劑是溴百里酚藍(lán)
Let's take a look at the spectrum
我們來看看光譜
Alright, so let's take a look at bromothymol blue
好，我們來看看溴百里酚藍(lán)
the indicator in the first set of cylinders
這是第一組柱形容器中的指示劑
As you can see here, there's a scale of numbers. This is the pH scale
這里可以看到一些數(shù)字刻度，這些是pH值刻度
The higher the number, the more basic the solution
pH值越高，表示溶液堿性越強(qiáng)
the lower the number, the more acidic
pH值越低，表示酸性越強(qiáng)
So our solution started off basic
我們的溶液最開始是堿性的
It was blue and had sodium hydroxide in it
它是藍(lán)色的，其中有氫氧化鈉
And this is what the chemical structure of the molecule looks like when it's blue
這是指示劑分子呈藍(lán)色時(shí)的化學(xué)結(jié)構(gòu)
The chemical bonds in the molecule are absorbing
分子中的化學(xué)鍵能夠吸收
colors of the visible spectrum that are not blue
藍(lán)色以外的可見光譜
so blue is reflected back to our eyes
所以藍(lán)色反射回我們的眼睛
Now if a compound picks up a hydrogen ion
但如果該化合物結(jié)合一個(gè)氫離子
which it would if you add an acid to it
加入酸時(shí)它確實(shí)會(huì)這樣
the molecule changes color
此時(shí)分子會(huì)變色
Now it absorbs blue and reflects yellow
它開始吸收藍(lán)光，并反射黃光
Since the colors depend on the structure of the molecule
由于顏色依賴于分子結(jié)構(gòu)
a chemist could reprogram the molecule to switch its color at
化學(xué)家可以重新構(gòu)造分子
other pHs, other numbers on this scale
讓顏色變化發(fā)生在其它pH值上
That's useful depending on the kind of reactions she may want to study
這對于所要研究的化學(xué)反應(yīng)很有用
Now nature experiments with color all the time
自然界也在不斷使用著顏色
Animals use color to avoid predators, attracts mates
動(dòng)物使用顏色來避開捕食者，吸引配偶
scare off enemies, etc
嚇退敵人，等等
Alright, so now let's take a look at
好，我們再來看看
what's happening in the second set of cylinders that started off pink
第二組最開始是粉色的柱形容器中發(fā)生了什么
The indicator in there is phenolphthalein
這里的指示劑是酚酞
The same thing is happening as with our bromothymol blue
情況和溴百里酚藍(lán)很類似
but this time when the solution is basic, it's pink
但這次，溶液呈堿性時(shí)，它是粉色
and when it's acidic, it's colorless
呈酸性時(shí)，則是無色
But why does adding dry ice
那么為什么加入干冰
change the solution from basic to acidic?
會(huì)讓溶液從堿性變?yōu)樗嵝阅?/div>
Well, dry ice is solid carbon dioxide
因?yàn)楦杀枪虘B(tài)二氧化碳
When you add it to water, it bubbles
加到水中時(shí)，它會(huì)冒泡
and part of every bubble of carbon dioxide dissolves
每個(gè)泡泡中都會(huì)有二氧化碳溶解
when it does, it forms carbonic acid. Let's look at that equation
這時(shí)就會(huì)生成碳酸，我們來看看方程式
So there's more and more carbonic acid in the water
水中的碳酸越來越多
and this acid reacts with the sodium hydroxide until there's none left
這種酸會(huì)同氫氧化鈉反應(yīng)，一直將其耗盡為止
So the solution becomes acidic
于是溶液變成酸性
So we saw our bromothymol blue
所以我們看到溴百里酚藍(lán)
turning from blue to yellow as a solution became more acidic
隨著溶液酸性越來越強(qiáng)，從藍(lán)變黃
And we saw our phenolphthalein
而酚酞
turn from pink to colorless as it became more acidic
隨著溶液酸性越來越強(qiáng)，從粉色變?yōu)闊o色
Now let's watch again what happens in the final set of cylinders
下面再來看看最后一組柱形容器中的實(shí)驗(yàn)
Alright, so now, I ask you to focus your attention on this cylinder
好，現(xiàn)在我要求你們注意這個(gè)柱形容器
Actually, you can focus your attention on anything you want to
實(shí)際上，你們也可以關(guān)注別的
You can even not pay attention if you want to
甚至不關(guān)注任何東西都行
We live in a free country
我們生活在一個(gè)自由的國度
But if you want to follow the experiment with me
但如果你想跟隨我的實(shí)驗(yàn)步伐
I want you to focus your attention on this one
我希望你能關(guān)注這個(gè)
and tell me, count them out how many different color changes you see
數(shù)一下我加入干冰后有多少種顏色變化
as I dropped the dry ice in there
數(shù)一下我加入干冰后有多少種顏色變化
I'm listening to you on the radio
我是在收音機(jī)前聽你們講
One, wow, I heard wow, what kind of account is that?
一，哇,我聽到有人說哇，這數(shù)的是什么
Three so far
目前我聽到三了
Three different color changes
三種不同顏色變化
but you know I'm listening to you on the radio
但我是在收音機(jī)前聽你們講
You want me to appreciate what you're seeing
你們要讓我理解你們看到了什么
So what were the color changes that you saw?
你們具體看到了什么顏色變化
Why couldn't you say those?
告訴我具體的
You see how we have to help our brain make the right observations
你們應(yīng)該知道如何幫助大腦作出正確觀測
and make the right reporting
并正確報(bào)告
OK so, in the final set of cylinders
在最后一組柱形容器中
Dr. Shakhashiri has a mixture of indicators
Shakhashiri博士使用了指示劑的混合物
This created the color changes that occurred as the solution became more and more acidic
這樣一來，隨著溶液酸性變強(qiáng)，顏色會(huì)多次變化
There were three changes that we saw
這里我們看到了三次變化
It went from purple to blue
首先是從紫色變?yōu)樗{(lán)色
to green
再變?yōu)榫G色
to yellow
再變?yōu)辄S色
Alright, that's it for me today
好，今天就到這里
I will see you next time
我們下次再見
