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打印
Hi, I'm Jessica
嗨，我是Jessica
and today I'm gonna be talking about a chemical demonstration I like to call
今天我要講的化學演示叫作
"mirror, mirror"
"魔鏡魔鏡"
In this demo, MIT's Dr. John Dolhun will demonstrate Tollens test
MIT的John Dolhun博士將演示Tollens測試
a chemical test created by this man, Bernard Tollens
這是由這個人，十九世紀末德國化學家
a German chemist born in the late 1800's
Bernard Tollens所發明的化學測試
So let's watch Dr. Dolhun perform this demonstration here at MIT
作為MIT劍橋科學節的一部分，來看看Dolhun博士
as part of the Cambridge Science Festival
是如何演示這個的
OK, so I'm gonna be careful
好，我要小心了
and I'm going to pour my first substance into the flask
首先將第一種物質倒入燒瓶
my second substance
然后是第二種物質
down to the last drop
倒完最后一滴
and my third substance
然后是第三種物質
and we're going to do a little shaking
搖一搖
for mixing some things together
讓它們能夠充分混合
So what did Dr. Dolhun do?
Dolhun博士做了什么呢
Well, he added three solutions to the flask
他往燒瓶中添加了三種溶液
Solution 1 was glucose in water
溶液一是葡萄糖水溶液
Solution 2 was a mixture of silver nitrate and ammonium nitrate
溶液二是硝酸銀和硝酸銨的混合溶液
And solution 3 was sodium hydroxide
溶液三是氫氧化鈉
which is a base
一種堿
So let's focus on the second two solutions first
我們先來看后兩種溶液
When you mix solutions 2 and 3, two things happen
溶液二三混合時，會發生兩件事
First, you form Ag20
首先會形成Ag2O
which is insoluble in water
它不溶于水
so it precipitates out as a brown solid
會作為褐色固體沉淀出來
The sodium hydroxide
氫氧化鈉
reacts with ammonium, NH4+
會同銨根離子NH反應
to produce ammonia,
NH3 生成氨 NH4
This dissolves the precipitate
這會溶解沉淀物
and you end up with Ag(NH3)2
最終得到Ag(NH3)2
which all has a positive charge
這整個帶有一單位正電荷
This is soluble in water and it's called Tollens reagent
它溶于水，叫作Tollens試劑
Now the positive charge is born by the silver
正電荷來自于銀離子
So we have in solution is essentially silver ions
溶液中基本上也就是銀離子
Now looking at solution 1
再看溶液一
glucose looks like this
葡萄糖是這樣的
We don't really care about this whole part of the molecule
分子的這一部分我們并不關心
So we're gonna call it R
可以記作R
for the rest
表示剩余部分
So glucose is basically this
葡萄糖可以寫成這樣
And this part of the glucose is going to start reacting with the silver ions
葡萄糖的這部分會同銀離子反應
Let's watch what happens
看看會發生什么
